JPS6293603A - Optical displacement measuring apparatus - Google Patents

Abstract

PURPOSE:To enable precise measurement even if there is minute displacement, by setting off the variation ready to generate by disturbance of the interval between the mirrors of a Fabry-Perot interferometer to which the reflective surface of a translucent mirror has been opposed by servo control. CONSTITUTION:Interference light generated by two translucent mirrors 6, 7 is detected by a photoelectric converting means 12 and the detected interference electric signal Is is amplified by a preamplifier 20 to be compared with reference voltage V0 corresponding to the middle point of interference by a comparator 21. The difference DELTAV between both of them is inputted to a drive amplifier 23 driving an electromagnetic coil 5 through a phase shifting circuit 22. Therefore, the electromagnetic coil 5 is excited according to the difference DELTAV and the translucent mirror 6 moves along with a wt. member 2 to be located at the position corresponding to the middle point of interference. When the positional change of the wt. member 2 is generated by acceleration in this state and the interval between two mirrors changes, the difference DELTAV comes to the value corresponding to acceleration and said value can be taken out from an output terminal 25.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical displacement measuring device, and more particularly to an optical displacement measuring device using a Fabry-Perot interferometer and servo control.

(Technical background of the invention) FIG.
Figure 2 shows a Fabry-Perot interferometer with two translucent 6M31.32 sheets facing inward toward each other. In the same figure, 3
5 is a transmitted interference light, and 36 is a reflected interference light, both of which are 2
The interference intensity changes depending on the spacing between the semi-transparent mirrors 31 and 32, but due to the periodicity and non-linearity of the interference, conventionally such an interferometer has not been suitable for measuring minute displacements.

That is, in this type of interferometer, when the distance between two mirrors facing each other changes due to disturbance or the like, the optical path phase changes and the interference intensity changes significantly. The transmitted interference intensity ■t of such an interferometer is expressed as the mirror reflectance R1 and the phase difference δ
As , it is expressed as . However, here, the phase difference δ is expressed as follows: λ is the expected wavelength, Da is the distance between the mirrors, and l is the displacement of the distance between the mirrors.

Moreover, the interference intensity I of the reflected light is It is expressed as

If the above equations (1) and (3) are illustrated, they are shown in FIGS. 4 and 5, respectively, and it can be seen that they have periodicity. Furthermore, it can be seen that the interference due to transmission and the interference due to reflection are in exactly opposite phases to each other. In addition, the fourth
In the figure and FIG. 5, m is an arbitrary integer. Also,
The curve in FIG. 4 shows a case where the reflectance R increases from top to bottom, and the curve in FIG. 5 shows a case where the reflectance R decreases from top to bottom.

By appropriately adjusting the spacing between the mirrors using the properties of such interference light, it is possible to detect changes in the displacement l near the midpoint of the interference intensity from changes in the interference intensity of transmitted light or reflected light. can.

However, in such an interferometer, the interference intensity is periodic, and the dynamic range is 1/1 of the wavelength λ of light in the positive and negative directions.
8, and the linearity is also very poor. Moreover, the mirror spacing is easily affected by temperature changes and changes over time, and there is a strong possibility that the operating point will be unclear from the beginning of setting.

Furthermore, devices based on the optical heterodyne method have been proposed as a means of measuring displacement continuously and analogously, but in order to continuously detect displacement, it is necessary to change the wavelengths of the interfering lights. Therefore, a wavelength shifter was used. However, wavelength shifters are expensive and increase the size of the device, making them undesirable. Furthermore, the stability of operation ζ was not fully satisfactory as described above.

Therefore, it has not been possible to actually use this type of interferometer as an industrial displacement measuring device.

(Objective of the Invention) The present invention was made in an attempt to eliminate the above-mentioned drawbacks of the prior art, and its purpose is to provide an optical displacement measuring device that can accurately measure even minute displacements. do.

Although the inventor of the present invention has already proposed an optical displacement measuring device to eliminate the drawbacks of the prior art described above (Japanese Patent Application No. 117420/1983), the present invention further improves the practicality of this device. It has been improved as follows.

(Summary of the Invention) In order to achieve the above-mentioned object, according to the present invention, the mirror spacing of a Fabry-Perot interferometer in which the reflective surfaces of semi-transparent mirrors are opposed to each other is controlled by servo control. The position change means mounted on at least one of the boundaries is controlled by an electrical signal so as to cancel the position by the electric signal.

In other words, the interference that occurs between two semitransparent mirrors adjusted in parallel is periodic (Fig. 4), and when the displacement l of the distance between the two semitransparent mirrors due to vibration is on the order of several microns, , as shown in FIG. 6, the phase difference δ changes in response to the displacement of this interval, resulting in a number of bright and dark interferences.

Even in such a case, if we focus on the minute portion near the center of the interference, the change in phase difference δ and the interference intensity are
As shown in the figure, there is a good proportional relationship. However, in general, the change in spacing due to vibration etc. is several microns or more, and it is not possible to consider only the minute part at the center of interference. Therefore, according to the present invention, the change in the phase difference δ due to the change in the distance between the two semi-transparent mirrors is compressed to a very small portion near the midpoint of interference.

Furthermore, in general, even when there is no vibration in the interval between two semitransparent mirrors, the midpoint of interference changes due to processing and adjustment accuracy, expansion and contraction due to temperature changes, and the like. Therefore, according to the present invention, by making it possible to automatically set one of the semitransparent mirrors to the midpoint of interference, it is possible to always obtain accurate measurement values.

Thus, for example, according to the invention, there is provided a first semi-transparent mirror having a reflective surface in the direction opposite to the direction in which the coherent measurement light of the light source arrives; a second semi-transparent mirror arranged so as to face each other; and the first or second semi-transparent mirror is mounted so that the measurement light can pass therethrough, and the light of the measurement light is transmitted by applying an electric signal.

and a position changing means displaceable in the axial direction.

Further, the optical displacement measuring device according to the present invention includes a lever, a first semi-transparent mirror having a reflecting surface in a direction opposite to the direction in which the coherent measurement light from the light source arrives; A second semi-transparent mirror is arranged so that its surface and its reflecting surface face each other, and the first or second semi-transparent mirror is mounted so that the measurement light can pass therethrough, and is moved forward by application of an electrical signal. A photoelectric conversion means for detecting the interference light formed and converting its intensity into an electric signal, and detecting the deviation of the DC component of the output electric signal of the photoelectric conversion means from the reference electric signal, and adjusting the position so that the deviation becomes zero. The changing means is provided on the driving electrical circuit.

Further, according to the optical displacement measuring device according to the present invention, the first semi-transparent mirror has a reflective surface in a direction opposite to the direction in which the coherent measurement light of the light source arrives; A second semi-transparent mirror is arranged so that its surface and its reflecting surface face each other, and the first or second semi-transparent mirror is mounted so that the measurement light can pass therethrough. a position changing means movable in the optical axis direction of the measuring light; and a first means for detecting transmitted interference light formed by the measuring light by the first and second semitransparent mirrors and converting its intensity into an electrical signal. a photoelectric conversion means, the first and the second
a second photoelectric conversion means for detecting the reflected interference light formed by the measurement light by the semi-transparent mirror and converting the intensity thereof into an electric signal, and a difference between the output electric signals of the first and second photoelectric conversion means and an electric circuit for driving the position changing means so that the position becomes zero.

Further, according to an embodiment of the present invention, the position changing means includes a magnetic field forming means that forms a constant magnetic field, and an electromagnetic means that is movable in the magnetic field in the optical axis direction of the measurement light. do.

Furthermore, according to an embodiment of the present invention, at least one of the magnetic field forming means and the electromagnetic means is an electromagnetic coil.

Furthermore, according to the embodiment of the present invention, the position changing means includes way 1 to members for detecting acceleration.

Note that in this specification, "displacement" includes both a unidirectional positional change and a reciprocating positional change such as vibration.

(Embodiments of the Invention) The present invention will be described in detail below with reference to the accompanying drawings. Note that the same reference numerals in each figure indicate similar objects.

FIG. 1 shows a measuring device according to an embodiment of the present invention, and shows a device for detecting vibration acceleration by transmission interference.

In the figure, 1 is a casing of the device, 2 is a weight member for detecting acceleration, 3 is a support means for elastically supporting this eight member, 4 is a magnetic field forming means and a magnetic circuit including a permanent magnet, 5 is an electromagnetic means, an electromagnetic coil, 6
and 7 is a semi-transparent mirror, 8 is a laser light source, 9 is a measurement light beam of light source 8, 10 is a collimation lens for converting measurement light 9 into a parallel light beam, and 12 is for detecting interference light formed by measurement light 9. 13 is a support plate supporting the semi-transparent mirror 7 and the photoelectric conversion means 12; 14 is an angle adjustment means for adjusting the support angle of the support plate 13; .

The casing l contains all the components for forming and detecting the transmitted interference light, but depending on the location where the device is fixed, it is not necessary or possible to install these in one casing. There is also. The material constituting the casing 1 can also be selected as appropriate.

A light source 8 such as a laser diode that generates coherent measurement light 9 is fixed to the frame member ID at the left end of the casing 1 . The light source 8 is not limited to a laser diode, and various light sources such as a gas laser can be used. The measurement light 9 emitted from the light source 8 is transmitted through a collimation lens 1 installed in the opening IF of the frame member ID.
At 0, it becomes a parallel light beam.

The weight member 2 has a cylindrical shape, for example, and has a central part thereof,
It has a through hole 2A that is substantially coaxial with the optical axis of measurement '#9, which will be described later. The measurement light 9 passes through this through hole 2A. An electromagnetic coil 5 is disposed near the surface of the measurement light incident side end of the weight member 2 along the two through holes. Further, a semi-transparent mirror 6 is fixed to the other end with its reflective surface 6R facing outward.

The support means 3 is an elastic member such as a spring, and the weight member 2 is arranged so that the measurement light 9 can pass through the two through holes.
support. Therefore, due to the presence of acceleration, the weight member 2 can freely move in the direction of the arrow X along the optical axis of the measurement light 9. The other end of the support means 3 is fixed to the casing 1.

The magnetic circuit 4 includes an electromagnetic coil 5 disposed on the weight member 2.
Together with this, it constitutes a position changing means for changing and controlling the position of the weight member 2. The magnetic circuit 4 has, for example, a flat cylindrical shape, and has a through hole 4A formed near the center thereof through which the measurement light 9 passes.

The semi-transparent mirror 6 fixed to the weight member 2 and the semi-transparent mirror 7 fixed to the support plate 13 have respective reflecting surfaces 6R.
, , 7R are arranged to face each other. Further, the angle of the support plate 13 is adjusted by the angle adjustment means 14 so that the respective reflecting surfaces 6R and 7R are substantially parallel. Although it is ideal that these reflective surfaces 6R and 7R are parallel to each other, they do not necessarily need to be parallel as long as interference occurs.

In the above, since the through holes and openings are all arranged coaxially, the light from the light source 8 is transmitted through the lens 10, the through hole 4A,
Through the two through-holes and the semi-transparent mirrors 6 and 7, the photoelectric
The conversion means 12 is reached.

FIG. 2 shows an electrical circuit for driving and controlling such a device. Terminal 15 of electromagnetic coil 5 and photoelectric conversion means 1
The terminal 16 of No. 2 becomes the ink face of this electric circuit and the configuration of FIG.

In the figure, 20 is a preamplifier that amplifies the interference electric signal IS obtained by the photoelectric conversion means 12 for subsequent processing;
1 is a comparator that outputs the difference ΔV between the reference voltage ■ applied to the terminal 24 and the interference signal Is; 22 is a phase shift circuit;
3 is a drive amplifier.

The connection order of the preamplifier 20 and the comparator 21 may be reversed, and in some cases, they may be combined into one circuit. The phase shift circuit 22 electrically differentiates the output signal ΔV of the comparator 21 to shift the phase of the interference electric signal and act to appropriately damp the vibration of the weight member 2.

The drive amplifier 23 is connected to one end of the terminal 15 of the electromagnetic coil 5, and amplifies the phase-shifted deviation signal Δ■ with current to drive the electromagnetic coil 5. A grounded load resistor R is connected to the other terminal 15 of the electromagnetic coil 5, and an output terminal 25 is drawn out from this connection point.

Note that the phase shift circuit 22, drive amplifier 23, etc. can be omitted depending on the case. For example, if the current sensitivity of the electromagnetic coil 5 is high or the output current of the preceding stage circuit is large, the drive amplifier 23 can be omitted.

In such a configuration, after the interference signals generated by the two semitransparent mirrors 6 and 7 are amplified, compared, and differentiated, the current flows through the electromagnetic coil 5 to correct the spacing between the semitransparent mirrors.
It forms a feedback loop that changes the interference strength. In this feedback system, it is necessary to consider the displacement of the position changing means with respect to the voltage and apply a feedback voltage that is sufficiently larger than the correction amount, and for this purpose, the gain of the amplification system including the preamplifier 20 must be made sufficiently large. There is a need to.

By the way, in the above-mentioned embodiment, the magnetic field forming means 4 is fixed to the casing 1, and the electromagnetic coil 5 is placed in a movable state. However, such a driving form is relative in the first place, and the fixed and movable modes may be reversed. That is, the electromagnetic coil 5 may be fixed to the casing l side, the magnetic field forming means 4 may be coupled and fixed to the weight member 2, and the magnetic field forming means 4 may be in a movable state. Furthermore, in the above description, in each case, one of the magnetic field forming means 4 and the electromagnetic coil 5 is in a fixed state and the other is in a movable state, but other means are also possible. Any means that can suppress the movement of the weight member 2 is sufficient. Therefore, when removed, the integrated magnetic field forming means 4
and the electromagnetic coil 5 are fixed on the casing 1 side, and a magnetic material such as iron is provided on the weight member 2 side, so that an electromagnetic force is generated between the magnetic field forming means 4, the electromagnetic coil 5, and the weight member 2. It is also possible to use a method that works.

Next, the principle and operation of the embodiment of this invention will be explained.

Prior to measurement, the unit shown in FIG. 1 is fixed to the object whose acceleration is to be measured (hereinafter referred to as the measurement object). The electrical circuit of FIG. 2 may be incorporated into the unit of FIG. 1 or may be separate.

First, a reference voltage (2) corresponding to the midpoint of interference is applied to the terminal 24 of the comparator 21. Therefore, when the object to be measured is stationary or moving at a constant speed, the acceleration is zero, and the mirrors 6 and 7
If the interval is a distance corresponding to the midpoint of interference, the deviation output signal ΔV of the comparator 21 is ΔV-0. Therefore, no current flows through the electromagnetic coil 5, and the weight member 2
Therefore, mirror 6 is also not driven.

However, in general, even in this state, the distance between the mirrors is not a distance that corresponds to the midpoint of interference.

The relationship between the interference intensities Ia, Ib, and Ic corresponding to the mirror spacings A, B, and C is shown in FIG.

The spacing and interference intensity Id show a relationship corresponding to the midpoint of interference.

Therefore, the output voltage of the preamplifier 20 is the reference voltage ■o(
! : Differently, the comparator 21 generates a corresponding output voltage ΔV, and the electromagnetic coil 5 is excited via the phase shift circuit 22 and the drive amplifier 23. Therefore, the weight member 2 and therefore the semitransparent mirror 6 move. This moving direction is determined by the winding direction of the electromagnetic coil 5 and the polarity of the magnetic circuit, electric circuit, etc. However, no matter which direction it moves, as the distance between the mirrors approaches the midpoint of interference, the difference between the reference voltage vo and the preamplifier output voltage becomes smaller, △V approaches zero, and the current flowing through the electromagnetic coil 5 decreases. Approach zero, and in this state the mirror (
5 stands still.

When the polarity of the electromagnetic coil, magnetic circuit, electric circuit, etc. is constant, the positions where the mirror rests are A and B' in Figure 9, respectively.
, the position indicated by C'. Interference intensity I' at this time
Strictly speaking, a, Ib, and I'c are the interference strengths corresponding to the midpoint of the interference ■d(!: are not equal, and are the amount of deviation from the initial midpoint and the current flowing to correct this deviation. This is the point where I'a, I 'b' and I'e' can be made approximately equal to the midpoint of interference.

The output signal of the comparator 21 at this equilibrium point is extremely small and has a value close to zero, but since it is amplified by the drive amplifier 23, the current necessary to correct the mirror spacing is passed through the electromagnetic coil 5. be able to.

As described above, with the semi-transparent mirror 6 positioned at the position corresponding to the midpoint of interference by the electrical servo operation,
Consider the case of detecting acceleration.

When the position of the weight member 2 changes due to acceleration and the distance between the two mirrors changes, the interference intensity of light also changes. Here, since the position change of the weight member 2 is continuous and changes gradually when viewed microscopically, the interference signal and the reference voltage are A current generated by the difference flows through the electromagnetic coil 5, and the semitransparent mirror 6 is always fixed at a position corresponding to the midpoint of interference. Strictly speaking, the semitransparent mirror 6 moves in response to the acceleration at a position slightly shifted from the position corresponding to the midpoint of interference.

In this case as well, the output signal of the comparator 21 is very small, but it is a value corresponding to the acceleration, and the drive amplifier 23
It becomes sufficient to drive the electromagnetic coil 5 and measure the acceleration.

By the way, in the servo geophone (the driven object of the servo system including the semi-transparent mirror 6), the spring constant of the support means 3 is ζ, the mass of the weight member 2 is m, and the sensitivity of the displacement of the position changing means to the current is A'. , the displacement detection and servo amount is A, and the acceleration in the X direction in Fig. 1 is a, the displacement X of the semi-transparent mirror 6 is:・・・・・・
・(4)k+A? A.

It can be expressed as From this equation (4), when the mass m of the weight member 2 and the spring constant k of the support means 3 are constant,
It can be seen that by increasing the servo amount A or the sensitivity A[, the displacement amount X of the servo geophone (semi-transparent mirror 6, etc.) can be made as small as desired.

Therefore, as shown in FIG. 10, the displacement X when the servo amount A is zero in fa) becomes small as the displacement X in bl in the same figure due to the servo operation.

Further, in accordance with this, the region in which the optical interference changes is limited to a very narrow range with good linearity, and it becomes possible to match displacement and interference and detect displacement from the interference signal.

Note that in equation (4), in the case of k〈AxAr,
The displacement amount X is A, Af゛° (5), and there is a linear relationship between the displacement amount X and the servo amount. Moreover, the output voltage e of the output terminal 25 in FIG. 2 is expressed as follows. Therefore, by increasing or decreasing the servo amount A, the displacement It becomes possible.

FIGS. 11 and 12 are diagrams showing the necessity of a modification of the embodiment of the present invention, and explanatory diagrams of the main parts of this modification.

That is, in a general Fabry-Perot optical system, the first
As shown in FIG. 1, the reflected light 30 from the two semi-transparent mirrors 6.7 returns to the laser light source 8, causing optical feedback, making the oscillation unstable and producing large noise light.

For this reason, as shown in FIG. 12, a polarizer 31 and a quarter-wave plate are provided on the return optical path of the reflected light 30 to block the reflected light before the light source 8. According to such a configuration, the light emitted from the laser light source 8 can pass through these optical elements, but the light 30 reflected by the semi-transparent mirror 6°7 is
The plane of polarization is rotated by the /4 wavelength plate 32 and the polarizer 3
1 cannot be passed.

Therefore, optical feedback to the laser light source 8 is almost eliminated.

FIG. 13 shows another modification of the embodiment of the present invention, which, like the modification shown in FIG. 12, aims to block the reflected light from the semi-transparent mirror 6.7.

That is, according to this variant, two semi-transparent mirrors 6.7
The angle with respect to the optical axis is slightly shifted from the right angle so that the reflected light 30 is absorbed by the light absorber 33. According to such a configuration, the purpose can be achieved without using expensive optical elements such as a 1/4 wavelength plate or a polarizer.

The material and shape of the light absorber 33 should be determined in consideration of optical conditions, and for example, Velvet Coat (trade name) can be used. Further, the angle of inclination of the mirror 6.7 should be appropriately determined in consideration of the detection sensitivity and the feedback rate of reflected light, but generally about 1 to 6 degrees is desirable. Note that it is not necessary to provide the light absorber 33 as long as the reflected light 30 does not return to the light source 8. For example, if the internal reflection of the casing 1 of the unit can be ignored, the light absorber 33 may be provided. There's no need.

In addition, in this case, as shown in FIG. 14, the weight member 2
Therefore, the moving direction of the semi-transparent mirror 6 is the incident direction 14 of the measurement light.
1, a direction 142 perpendicular to the mirror 7, and a traveling direction 143 of the reflected light 30. This is because the difference between these three directions is slight and there is no significant difference in detection sensitivity.

FIG. 15 shows another embodiment of the present invention, in which fluctuations in the power of the laser beam and noise contained in the laser beam are suppressed.

That is, as described above, the power fluctuation and noise component of the laser light source included in the output of the preamplifier 20 cannot be distinguished from the interference component due to vibration displacement, and the comparator 21 processes the noise component such as the power fluctuation as a change in interference. do. Therefore, the comparator 21 outputs the difference between the reference voltage Vo and the power fluctuation noise component, and performs a servo operation similar to normal acceleration detection.

If this is expressed as an approximate expression, the output signal of the preamplifier 20 will be:
The relationship representing the interference intensity It, where the incident light power is E, is It=E (1+a CO3δ)・−・・・・・・・・・・
As a result, the output Ed of the comparator 21 is E (y= E −Vo+E Rcosδ・・・・・・
. . . (8), which includes a noise component called E-Vo. Even if power fluctuations among such noise components can be suppressed by power control, it is difficult to reduce other noise components, which may interfere with the measurement of minute accelerations. This embodiment solves this problem.

That is, according to this embodiment, in addition to the electric circuit of the embodiment of FIG. 2, fluctuations in the optical power of the laser light source 8 are detected by the power supply circuit 40 and the reference voltage V is determined. Gain adjustment circuit 4 that gives
1. That is, in general, laser light sources such as semiconductors have large power fluctuations due to external factors, so the power supply is equipped with an optical power control circuit. For example, in the case of a semiconductor laser, a photodiode for power control is built into the laser case, which detects the optical power of the laser beam and controls the power supply circuit 40 to keep the optical power constant. ing. In this case, the output of the photodiode includes noise from the laser light source as well as a small amount of noise generated by the photodiode itself.

In this case, the output of the photodiode corresponds to the laser light power E, and can be expressed as αE, where α is a constant determined by the photodiode or the like. For this reason,
The output of this photodiode is passed through a gain adjustment circuit 41 with a gain of 1/α to obtain an output voltage E, and the input of the terminal 24 of the comparator 21 is set to a reference voltage V. You can touch it.

In this case, the output P, d of the comparator 2I is Eel=E
(1+Reosδ) −E=E・Rcosδ ・・・・
...pause...song, song, song... (becomes 9+,
Noise components do not appear.

FIG. 16 shows still another embodiment of the present invention, in which both the transmitted interference light and the reflected interference light are used to suppress noise (similar to the previous embodiment).

According to this embodiment 1, the transmission interference light detection system is an improved version of the above-mentioned version. is provided, and the reflected light is detected by the photoelectric conversion means 50.

The output signal of this photoelectric conversion means 50 is amplified by a preamplifier 29, and then one input of the comparator 21 (reference voltage input)
becomes.

According to such a configuration, the reflected interference intensity I of equation (3),
, Ir=E (1-Rcosδ)・・・・・・・・・
If expressed approximately by (10), the output Bg of the comparator 21 is obtained by the difference between equation (7) and equation (10), and E(1=2 ERcosδ・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・(1])
It can be seen that no noise component is output.

This situation is schematically shown in FIG. 17, which also shows transmission interference and reflection interference in FIGS. 4 and 5. According to the figure, initially, when the mirror spacing was A, the interference intensities of transmission and reflection were ■Ar and IAt, respectively, but the interference intensity was executed by the difference signal, and finally 2 The two interference intensities match, and the mirror spacing has settled at A'.

The advantage of this method is that the noise of the laser light source is not output, and by taking the difference between the transmitted interference and the reflected interference, it is possible to avoid any increase in the size of the device.

FIG. 18 shows still another embodiment of the present invention, and shows an electrical configuration for adjusting the parallelism of two semi-transparent mirrors 6 and 7.

In the figure, 61 is an oscillator for alternately exciting the electromagnetic coil 5 at a frequency of several tens to several hundred hertz, 62 is an amplitude-to-voltage converter, and 63 is a voltmeter.

According to such a configuration, the mirrors 6 and 7 once adjusted parallel to each other
However, if the settings deviate from the initial settings due to shock during transportation, etc., readjustment becomes possible.

That is, due to the activation of the oscillator 61 for adjustment, the coil 5 periodically vibrates, causing an interference change. The interference in this case has periodicity corresponding to the oscillation frequency, as shown in FIG. 19.

In this case, the difference between the maximum value and the minimum value of interference, that is, the degree of interference, does not depend on the current flowing through the coil, but depends on the parallelism of the two semitransparent mirrors. If the parallelism is good, see Figure 20 (
The interference signal becomes large as shown in FIG. 21), and when the parallelism is poor, the interference signal becomes small as shown in FIG. 20(b). Therefore, rather than inputting the output of the preamplifier 20 into the amplitude-to-voltage converter 62i and adjusting the angle with the angle adjusting means 14, the parallelism of the mirror is monitored while monitoring the output voltage of this converter 62 with the voltmeter 63. Can be checked. It is easy to understand that the best time for the value of the voltmeter 63 to be the maximum is when the parallelism is the best.

According to such an embodiment, since the degree of interference does not depend on the frequency of the oscillator or the current flowing through the coil, there is no need to use a highly accurate and stable oscillator, and the parallelism of the mirror can be adjusted easily and inexpensively. It is practical and can be carried out.

Alternatively, the electromagnetic coil 5 can be wound twice, a direct current for adjusting the distance between the mirrors can be passed through one coil, and the other coil can be used as a coil for servo operation.

That is, in order to perform the servo operation smoothly, as mentioned above, it is necessary that k Depending on the installation conditions of the device, the two translucent mirrors may come into contact with each other, the weight member may come into contact with the stopper (not shown) or the surrounding area, or the spring elasticity limit of the support means may be exceeded. .

In order to prevent these problems, it is possible to increase the distance between the respective constituent elements, but this is not desirable because the influence of the wavelength fluctuation of the light source increases.

This means that in equation (3), λ<<96. l=0
Then, it becomes as follows, and it can be seen that the interference intensity changes greatly with a very small wavelength variation.

Therefore, with this configuration in which the electromagnetic coils are doubled, regardless of the installation conditions such as the installation angle of the two semitransparent mirrors, they can be placed relatively close to each other (for example, about 0.1 mm) apart. 2 can be kept constant. More specifically, the semi-transparent mirrors 6 are displaced by the current flowing through the coil, and can be set at intervals that are less susceptible to changes in the wavelength of the light source and at positions where the support means can move smoothly. .

This invention is not limited to the above embodiments and modifications, and various other embodiments and modifications are possible within the technical scope of this invention, and equivalent components may be replaced. It will be clear to those skilled in the art that this is possible. For example, in each of the above embodiments, the purpose is to detect acceleration, but the invention is not limited to this. Further, the position changing means is not limited to electromagnetic means, and for example, displacement of a piezoelectric element can be used.

(Effects of the Invention) According to the present invention, by combining the servo control with the 7-Avri-Perot interferometer as described above, the Guinamino cleanliness and linearity of the measurement are greatly improved, and it is possible to overcome any changes. An optical displacement measuring device capable of accurate measurement can be obtained.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a measuring unit of an optical displacement measuring device according to an embodiment of the present invention, FIG. 2 is an electrical system diagram for operating the unit of FIG. 1, and FIG. 3 is a principle of the present invention. FIGS. 4 and 5 are general illustrations of transmission interference and reflection interference, respectively. FIG. 6 is a general illustration of the operation of the Fabry-Perot interferometer, and FIGS. 7 and 10.
The figure is an explanatory diagram of the operation of the embodiment of the present invention, FIGS. 11 and 12 are diagrams showing the necessity of a modification of the embodiment of FIG. 1 and a modified example, and FIG. 13 is an implementation of the embodiment of FIG. 1. Another modification of the example, FIG. 14 is an explanatory diagram of the operation of the modification of FIG. 13, FIG. 15 is an explanatory diagram of an optical displacement measuring device according to another embodiment of the invention, and FIG. 16 is an illustration of the invention. FIG. 17 is an explanatory diagram of the operation of the embodiment of FIG. 16, and FIG. 18 is an optical displacement measurement device according to still another embodiment of the present invention. Explanatory diagram of the device, Figures 19 and 20
The figure is an explanatory diagram of the operation of the embodiment of FIG. 18. ■...Casing, 2...Weight member, 3...
Supporting means, 4... Magnetic amplifier which is a component of the position changing means, 21... Comparator, 23... Drive amplifier, 4]... Gain adjustment circuit.

Claims (1)

[Claims] 1. A first semi-transparent mirror having a reflective surface in a direction opposite to that in which the coherent measurement light of the light source arrives, and the reflective surface of this semi-transparent mirror and its reflective surface mutually A second semi-transparent mirror arranged to face each other, and the first or second semi-transparent mirror are mounted so that the measurement light can pass therethrough, and the direction of the optical axis of the measurement light is adjusted by applying an electric signal. Alternatively, an optical displacement measuring device comprising a position changing means that can be displaced in a direction substantially equal to the optical axis direction. 2. A first semi-transparent mirror having a reflective surface in the direction opposite to the direction in which the coherent measurement light of the light source arrives, and the reflective surface of this semi-transparent mirror and the reflective surface thereof are arranged so as to face each other. A second semi-transparent mirror, and these first or second semi-transparent mirrors are mounted so that the measurement light can pass therethrough, and by applying an electric signal, the measurement light is moved in the optical axis direction of the measurement light or approximately in the optical axis direction. a position changing means that can be displaced in the same direction; a photoelectric conversion means that detects interference light formed by the measurement light by the first and second semitransparent mirrors and converts its intensity into an electrical signal; this photoelectric conversion means an electric circuit that detects a deviation of a DC component of an output electric signal from a reference electric signal and drives the position changing means so that the deviation becomes zero. 3. A first semi-transparent mirror having a reflective surface in the direction opposite to the direction in which the coherent measurement light of the light source arrives, and the reflective surface of this semi-transparent mirror and the reflective surface thereof are arranged so as to face each other. A second semi-transparent mirror, and these first or second semi-transparent mirrors are mounted so that the measurement light can pass therethrough, and by applying an electric signal, the measurement light is moved in the optical axis direction of the measurement light or approximately in the optical axis direction. a position changing means that can be displaced in the same direction; and a first photoelectric conversion means that detects transmitted interference light formed by the measurement light by the first and second semitransparent mirrors and converts its intensity into an electrical signal. , a second photoelectric conversion means for detecting reflected interference light formed by the measurement light by the first and second semi-transparent mirrors and converting the intensity thereof into an electric signal; and these first and second photoelectric conversion means. and an electric circuit that drives the position changing means so that the difference between the output electric signals of the means becomes zero. 4. In the apparatus according to any one of claims 1 to 3, the position changing means includes a magnetic field forming means for forming a constant magnetic field, and a magnetic field forming means for forming a constant magnetic field, and a direction in the optical axis direction of the measurement light in the magnetic field. , or an electromagnetic means movable in a direction substantially equal to the optical axis direction. 5. The optical displacement measuring device according to claim 4, wherein at least one of the magnetic field forming means and the electromagnetic means is an electromagnetic coil. 6. An optical displacement measuring device according to any one of claims 1 to 5, wherein the position changing means includes a weight member for detecting acceleration. 7. A first semi-transparent mirror having a reflecting surface in a direction opposite to the direction in which the coherent measurement light of the light source arrives, and the reflecting surface of this semi-transparent mirror and its reflecting surface are arranged so as to face each other. A second semi-transparent mirror, and these first or second semi-transparent mirrors are mounted so that the measurement light can pass therethrough, and by applying an electric signal, the measurement light is moved in the optical axis direction of the measurement light or approximately in the optical axis direction. a position changing means that can be displaced in the same direction; a photoelectric conversion means that detects interference light formed by the measurement light by the first and second semitransparent mirrors and converts its intensity into an electrical signal; and the position changing means an oscillator that periodically excites the voltage, a converter that converts the amplitude of the output electrical signal of the photoelectric conversion means into a voltage value corresponding to the amplitude, and a display means that displays the output voltage of the converter, An optical displacement measuring device configured to detect the parallelism of the first and second semi-transparent mirrors based on the magnitude of the voltage value.