JP3519864B2 - Vibration pickup calibration device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a calibration device for a vibration pickup such as a piezoelectric type, a servo type, and a velocity type used for measuring vibrations, and more particularly to a calibration device by a dynamic method using a sine wave.

[0002]

2. Description of the Related Art Conventionally, the sensitivity S of a vibration pickup is measured by measuring an accurate vibration acceleration A [m / s ² ] of a vibration exciter with a laser beam and by measuring an output V [mv] of the vibration pickup. = V / A [mv / m · s ^-2 ] is known. A Michelson type light wave interferometer is generally used to measure the vibration acceleration (amplitude) by the laser light.

Here, the principle of measuring the amplitude of laser light by the Michelson type light wave interferometer will be described. In FIG. 4, the laser light emitted from the light source (laser emitter) 1 travels straight about half by the beam splitter (split mirror) 2 and is reflected by the other half, and the reference mirror (fixed mirror) 3 and the additional mirror, respectively. The light is reflected by the mirror 4a fixed to the shaker, is combined again, and enters the light receiver 5. Reference numeral 6 in FIG. 4 indicates an optical axis (laser beam axis) between the mirror 4a and the beam splitter 2.

Here, E ₀ , E ₁ and E ₂ are the electric field vectors of the reflected light from the light source 1, the reference mirror 3 and the reflected light from the mirror 4a, and l ₁ and l ₂ are the beam splitters 2 and 2 respectively. Letting the actual optical path length between the mirror 3 and the mirror 4a as an oscillating mirror be d, and the measured displacement of the mirror 4a be d, the electric field vectors E ₁ and E ₂ are expressed by [Equation 1] and [Equation 2]. be able to.

[Equation 1]

[Equation 2] Here, λ is the wavelength of the laser light.

The luminance I (t) of the light beam incident on the light receiver (light wave detector) 5 is given by the formula [3].

[Equation 3] I (t) = │E ₁ + E ₂ │ ² = A + B cos [4π / λ ・
(L + d)] Here, A and B are constants of the system, and if L = l ₂ −l ₁ , it can be seen from the formula [3] that the maximum luminance occurs under the condition of the formula [4]. .

(4) 4π / λ · (l ₂ −l ₁ + d) = 2nπ

Further, the displacement d corresponding to the distance between the two maximum luminances is given by λ / 2. Therefore, the maximum brightness number Rf during one cycle is expressed by the equation [5].

[Equation 5] Since Rf is obtained by dividing the number N of interference stripes (fringes) counted in one second by the vibration frequency of the mirror, it is generally called "frequency ratio".

The displacement amplitude a ₀ is given by the equation [6].

[6] Therefore _{a 0 = Rf · λ / 8} , by measuring the frequency ratio and frequency, it is possible to calculate the velocity and acceleration. (This method is also called "interference stripe counting method".)

FIG. 7 shows the vibration waveform d (t) of the mirror and the interference waveform I (t) of the interference light. Since this figure assumes that the amplitude a ₀ is equal to the wavelength λ of the laser light, the number of interference fringes is 8. Since the number N of the interference fringes generated by the mirror in one cycle is determined by the ratio between the excitation frequency f _m and the frequency f _i of I (t), the formula [7] is established.

[Mathematical formula-see original document] a ₀ = (λ / 8) · (f _i / f _m ) Measuring the number of interference fringes means setting a certain threshold value (shown by the dotted line f _i in FIG. 7) and setting this value to To count the number of times you go from bottom to top (or top to bottom).

In a measurement system using such a Michelson type light wave interferometer, a conventional calibration device has a phototransistor 15a as a photoelectric conversion element installed in a light receiver as shown in FIGS. Is being detected. Figure 5,
In FIG. 6, reference numeral 4 indicates a vibration exciter, a vibration pickup 10 is attached to the vibration exciter 4, and a mirror 4a as a vibrating mirror is attached to the end face thereof. The vibrator 4 and the laser oscillator 1 are mounted on a common heavy vibration isolator 30. As shown in FIG. 6, the vibration pickup 10 is composed of a base 10a, a piezoelectric element 10b and a mass 10c, and the output of the piezoelectric element 10b is used as the output of the vibration pickup 10 via a preamplifier 11 and an RMS voltmeter. 12, a mirror 4a is attached to the right end surface of the base 10a.

The interference fringes detected by the phototransistor 15a pass through the preamplifier 13, the amplifier 14 and the pulse generator 16,
Input to the ratio counter 20. Further, the signal is input to the filter 21 via the amplifier 14, and only the frequency component of the vibrating mirror is extracted from the interference fringe in the filter 21 and input to the oscilloscope 22 and the voltmeter 23. Reference numeral 17 denotes an oscillator of the vibration exciter 4, and the oscillator 17 is provided with an output adjusting volume 17a of the vibration exciter 4. The output of the oscillator 17 is transmitted to the vibration exciter 4 via the power amplifier 18.

In counting the number of interference fringes, the waveform I (t) of the interference fringes is positive or negative every time a certain threshold (f _{i in} the case of FIG. 7) is passed from bottom to top and from top to bottom. The square wave Q is generated by the pulse generator (see FIG. 7), and based on this square wave, the ratio counter 20 calculates the ratio between the frequency f _{m of the} vibration exciter and the frequency f _{i of the} interference fringe and digitally calculates it. It is displayed and the number of interference fringes is counted. That is, in the square wave generator 16, a square wave Q is generated as shown in FIG. 7 every time the waveform It crosses the 0 line (threshold value) from bottom to top and from top to bottom. As is clear from FIG. 7, the square wave is equal to the period of the wave (waveform It) of the interference fringe. The square wave generator 16 is provided to make the operation of the ratio counter 20 more reliable and may be omitted. Then, this square wave Q is input to the ratio counter,
Here, the frequency f _{i of the} interference fringe calculated from the number of square waves Q
And the vibration frequency f output from the oscillator 17 to the vibration exciter 4.
The ratio f _i / f _m and _m is calculated, the calculated value is digitally displayed.

[0012]

In the Michelson type light wave interferometer described above, a mirror is attached to the end surface of the vibration pickup, so that the end surface of the vibration pickup is accurately perpendicular to the optical axis. , It is assumed that the vibration pickup is mounted on the shaker. By the way, generally, in the vibration pickup, the mounting surface for the vibration exciter and the end surface for mounting the mirror are not always formed completely parallel to each other. Therefore, conventionally, in the calibration, the position of the phototransistor and the angle of the reference mirror are finely adjusted so that interference fringes are formed on the photodetector after the vibration pickup is attached to the vibration exciter.

This fine adjustment needs to be performed every time the vibration pickup is replaced, which requires a great deal of labor and time, which causes a problem of inefficient calibration. Further, there is a problem that the interference surface is changed each time by fine adjustment, and stable measurement is difficult. The present invention is intended to solve such a problem, and a vibration exciter to which a vibration pickup is attached,
A laser emitter, a mirror attached to the end face of the vibration pickup, a reference mirror as a fixed mirror, and a beam splitter for splitting the laser light emitted from the laser emitter into the mirror and the reference mirror, A laser interferometer comprising a photoelectric conversion element for detecting an interference fringe generated by the laser light reflected by the mirror and the laser light reflected by the reference mirror of the laser light, and the laser light emitter and the beam splitter. To provide a calibration device for a vibration pickup characterized in that a noble mechanism for adjusting an optical axis is provided on the optical axis between the optical axis and the reflected laser light from the mirror to match the bright points of the reflected laser light from the reference mirror. With the goal.

[0014]

SUMMARY OF THE INVENTION The present invention is directed to a vibrator to which a vibration pickup is attached, a laser emitter, a mirror attached to the end face of the vibration pickup, a reference mirror as a fixed mirror, and the laser. A beam splitter that splits the laser light emitted from the light emitter into the above-mentioned mirror and reference mirror, and interference fringes generated by the interference of the laser light reflected by the mirror and the laser light reflected by the reference mirror. equipped with a light wave interferometer, which is formed of the photoelectric conversion element for detecting, between said mirror and said beam splitter
In addition, the irradiation light to the mirror and the reflection from the mirror
An optical axis adjustment mechanism that adjusts the optical axis of light is provided to solve problems.
It is stepwise.

The optical axis adjusting mechanism has at least one optical axis adjusting mechanism.
Each optical wedge is used as a means to solve the problem. Further, the optical wedge is rotatably arranged to solve the problem. Further, the above-mentioned optical wedge is arranged so as to be movable in a direction parallel to the optical axis as means for solving the problem. Further, a pair of the optical wedges are arranged in the optical axis direction, and the same pair of optical wedges are formed so as to be movable in a direction parallel to the optical axis as a whole, as a means for solving the problem. The optical wedge is formed of a transparent material having a surface perpendicular to the central axis and an inclined surface inclined to the surface perpendicular to the central axis, and the central axis is aligned with the optical axis. And is used as a means for solving the problem.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A vibration pickup calibrating apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram thereof, FIG. 2 is a side sectional view of an essential portion thereof, and FIG. It is a perspective view of the wedge.

In this embodiment, the Michelson type light wave interferometer as shown in FIG. 1 is used as the light wave interferometer. The light wave interferometer of FIG. 1 is the same as that of FIG. 5 except that the phototransistor as the photoelectric element in the Michelson type light wave interferometer shown in FIG. 5 is replaced by the photodiode 15. The same vibration pickup 10 as that shown in FIG. 6 is used. And
An optical axis adjusting mechanism 7 as shown in FIG. 2 is interposed in the optical axis 6 between the mirror 4a and the beam splitter 2, that is, in the middle of the optical axis 6 of the irradiation light to the mirror 4a and the reflected light from the mirror 4a. Has been done. In the optical axis adjusting mechanism 7, a pair of optical wedges 8 made of a transparent material as shown in FIG. 3 make the inclined surfaces of the optical wedges 8 face each other, and center around the central axis 0-0 of each optical wedge 8. It is configured to be rotatably attached to the vibration isolation table 30. As shown in FIG. 3, the wedge 8 forms a vertical surface 8a that is perpendicular to the central axis 0-0 and an inclined surface 8b that forms an opposite side surface of the vertical surface 8a and that is inclined by approximately 3 ° with respect to the vertical surface 8a. Is formed of a transparent material.

An optical wedge 8 having such a shape is constituted by a ring-shaped holding member 9a and a ring-shaped mounting member 9b capable of holding the optical wedge 8 together with the holding member 9a, and a wedge-holding annular member 9 is formed. Is supported by. The outer shape of the annular member 9 is circular, and the slider 31 movably arranged on the vibration isolation table 30 in the direction parallel to the optical axis 6 rotates the center axis 0-0 of the optical wedge 8 as the center of rotation. It is attached so that it can be rotated. Reference numeral 32 denotes a support member that is embedded in the slider 31 and that supports the annular member 9 so as to be rotatable (rotation around the central axis 0-0 of the optical wedge 8). The holding member 9a, the mounting member 9b, and the support member
In each of the 32 members, small holes 9c, 9d, 32a for passing laser light are formed at the center.

The above is the support structure for the right optical wedge 8A in FIG. 2, but the left optical wedge 8B in FIG. 2 is also supported by the vibration isolation table 30 by the same support structure. In the above configuration, by rotating one or both of the pair of optical wedges 8, the optical axis 6 (direction thereof) between the mirror 4a and the beam splitter 2 can be continuously adjusted. Therefore, the vibration pickup 10 is attached to the vibration exciter 4, and the optical wedge 8 is rotated while irradiating the laser beam, whereby the fine adjustment of the measurement system for generating the interference fringes in the photodetector 5 is easily performed. It is possible to improve work efficiency. At that time, since the position of the light receiving element 15 and the position of the reference mirror 3 do not change, the interference surface can be fixed, interference fringes having a high contrast ratio can be formed, and stable measurement can be performed.

The number of optical wedges 8 may be one. However, when the number of optical wedges is one, the amount of adjustment of the optical axis is smaller than that when the number of optical wedges is two. Further, when the number of optical wedges 8 is two, the inclined surfaces of both wedges do not necessarily have to be arranged to face each other. Also in this case, the optical axis adjustment amount is smaller than that in the case where the inclined surfaces of both wedges are arranged to face each other (the case of FIG. 2). Further, the slider 31 is moved in a direction parallel to the optical axis 6, that is, the distance between one optical wedge 8 or two optical wedges 8 and the mirror 4a is adjusted, or two optical wedges are adjusted. By adjusting the distance between the wedges 8 and 8, the direction of the optical axis can be adjusted, and when the rotation and position of the optical wedge 8 and the adjustment of the distance between the two optical wedges are combined, a large light beam is emitted. The amount of axis adjustment can be obtained.

[0021]

As described above in detail, according to the vibration pickup calibration apparatus of the present invention, in the vibration pickup calibration apparatus using the Michelson type optical interferometer, the measurement system is adjusted to generate the interference fringes. It is possible to simplify the adjustment when performing the adjustment, and improve the efficiency of the calibration work of the vibration pickup. Furthermore, since the position of the light receiving element 15 and the position of the reference mirror 3 do not change, the interference surface can be fixed, interference fringes having a high contrast ratio can be formed, and stable measurement can be performed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a vibration pickup calibration apparatus according to an embodiment of the present invention.

FIG. 2 is a side sectional view of the same main part.

FIG. 3 is a perspective view of the wedge.

FIG. 4 is a schematic configuration diagram of a Michelson type light wave interferometer.

FIG. 5 is a schematic configuration diagram of a vibration pickup calibration apparatus using a conventional Michelson-type light wave interferometer.

FIG. 6 is an enlarged view of part A in FIG.

FIG. 7 is a graph showing a waveform [I (t)] of interference fringes and a square wave [Q] based on the same waveform in a Michelson light wave interferometer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Laser light emitter (light source) 2 Beam splitter 3 Reference mirror 4 Exciter 4a Mirror as an oscillating mirror 5 Light receiver 6 Optical axis 7 of laser light emitted and reflected by the mirror 7 Optical axis adjusting mechanism 8 Optical wedge 8a Vertical surface 8b Inclined surface 9 Wedge holding annular member 9a Holding member 9b Mounting member 10 Vibration pickup 12 RMS voltmeter 15 Phototransistor 30 as light receiver 30 Vibration isolation table 31 Slider 32 Supporting member

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoya Hu, 430-1 Kamiyokoba, Tsukuba, Ibaraki Mitsutoyo Tsukuba Research Institute (56) References JP-A-5-203409 (JP, A) JP-A-6- 341809 (JP, A) JP 56-128407 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01H 9/00 G01H 17/00 G01P 21/00

Claims (6)

(57) [Claims] 1. A vibrating machine to which a vibration pickup is attached, a laser emitter, a mirror attached to an end face of the vibration pickup, a reference mirror as a fixed mirror, and a laser beam emitted from the laser emitter. From a beam splitter that divides the above into a mirror and a reference mirror, and a photoelectric conversion element that detects an interference fringe generated by interference between the laser light reflected by the mirror and the laser light reflected by the reference mirror of the laser light. And a light wave interferometer between the mirror and the beam splitter.
Adjust the optical axis of the illuminating light and the reflected light from the mirror.
It is characterized in that an optical axis adjusting mechanism for adjusting is provided.
A vibration pickup calibration device. 2. The apparatus for calibrating a vibration pickup according to claim 1, wherein the optical axis adjusting mechanism has at least one optical wedge. 3. The calibration device for a vibration pickup according to claim 2, wherein the optical wedge is rotatably arranged. 4. The optical wedge is arranged so as to be movable in a direction parallel to the optical axis.
Or the calibration device of the vibration pickup according to the item 3. 5. A pair of the optical wedges are arranged in the optical axis direction, and the same pair of optical wedges are movable in a direction parallel to the optical axis as a whole. 5. The vibration pickup calibration device according to any one of items 1 to 4. 6. The optical wedge is formed of a transparent material having a surface perpendicular to the central axis and an inclined surface inclined to the surface perpendicular to the central axis, and the central axis coincides with the optical axis. Characterized in that they are arranged,
The calibration device for a vibration pickup according to claim 2.