JP3108866B2 - Laser vibration displacement measuring 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 laser reference beam for irradiating an object to be measured and a beat component generated by reflected light from the object to be measured having a phase difference between the reference light and the reference light. The present invention relates to a device for measuring the speed and vibration displacement of an object in a non-contact state. The present invention belongs to the technical field of laser measuring instruments, and is used in a wide range of fields that require measurement of minute vibrations, including quality inspection to guarantee the eccentricity of industrial precision motors. ing.

[0002]

2. Description of the Related Art An outline of the configuration of a conventional laser vibration displacement measuring device and a basic operation principle will be described below with reference to FIG. In the laser vibration displacement measuring device 31, the laser light oscillated by the laser oscillating device 2 is split into two light waves by the beam splitter 3a. One light wave passes through the acousto-optic converter 4 and gives a frequency shift due to optical heterodyne. At this time, the acousto-optic converter 4 is driven by a constant frequency signal from the beat frequency oscillator 7. The light wave having the frequency shift is guided to the photoelectric converter 6 via the beam splitter (half mirror) 3c. on the other hand,
The light wave that has passed through the beam splitter 3a is applied to the device under test 8 via a beam splitter (half mirror) 3b. At this time, when the DUT 8 is vibrating, the reflected light from the DUT 8 undergoes a frequency shift proportional to the speed of the DUT 8 due to the Doppler effect. The reflected light that has undergone the frequency shift due to the Doppler effect is optically arranged and adjusted so as to be guided to the photoelectric converter 6 by the beam splitter 3 b and the mirror 5. In the photoelectric converter 6, as a result of the two light waves having different frequencies overlapping, a beat component is generated in the light amplitude. The beat component is converted from light into an electric signal by the photoelectric converter 6. Since the electric signal including the beat component obtained here is generally weak, the electric signal is amplified using the amplifier 11. By using the F / V converter 33, the frequency reflecting the speed of the device under test 8 can be adjusted by the amplifier 1
1 from the output signal. When determining the speed of the device under test 8, the output of the F / V converter 33 is extracted as a speed signal b. On the other hand, when determining the displacement of the device under test 8, the output of the F / V converter 33 is integrated by the integrator 34, and the displacement signal a is extracted as a voltage output corresponding to the displacement. The signal switch 3 for detecting the output offset of the F / V converter 33 when the speed of the device under test 8 is zero.
2, the output of the photoelectric converter 6 is sent to the amplifier 11 at the time of measurement, and the output of the beat frequency oscillator 7 is sent to the amplifier 11 at the time of confirming the offset.

[0003] On the other hand, a displacement meter based on the principle of triangulation is also used. This principle is based on obliquely irradiating a laser beam to an object and receiving light reflected by the object (distance between light emission and light reception). ) Is a distance from the object to be measured.

[0004]

In the case of a conventional laser vibration displacement measuring device, a signal corresponding to the speed of an object to be measured is F /
If the speed of the device under test is extremely small with respect to the speed detection range, or if the vibration frequency of the device under test is extremely low with respect to the frequency of the beat frequency oscillator, sufficient output can be obtained. Can not be obtained. For example, in the case of measurement in a frequency band of 1 kHz or more in which the speed of the device under test is relatively large, the signal component reflecting the speed of the device under test has a large S / N ratio, so that measurement with high measurement accuracy is performed. It is possible. However, when the speed of the device under test decreases and the frequency band is 100 Hz or less, the signal component reflecting the speed of the device under test decreases as the frequency decreases, and the S / N ratio in the F / V converter significantly increases. Because of the decrease, even if the displacement is obtained by integrating the signal, the result is extremely lacking in reliability. For example, a wavelength of 632.8 nm
When a 20 Hz vibrating body is measured by using the red laser light, a clear noise of about 1 μm is generated. This means that it is impossible to measure the amplitude of a vibrating body having an amplitude of about 1 μm using a conventional laser vibration displacement measuring device.

If the measurement speed range and the measurement vibration frequency range are narrowed to improve the S / N ratio, it takes time for F / V conversion, and it is difficult to detect irregular speed changes or displacements. As a matter of course, it is impossible to measure an extremely slow displacement of the object to be measured which is almost stationary. On the other hand, the displacement meter based on the principle of triangulation makes it difficult to achieve both the measurement resolution and the measurement range due to the limitations of the size and resolution of the detector, and furthermore, the distance between the measuring device / detector and the object to be measured is limited. It was not easy to use.

In general, when a minute vibration measurement such as a quality inspection for guaranteeing the eccentricity accuracy of an industrial precision motor is required, the vibration frequency of the object to be measured is unknown, and the vibration in a wide vibration frequency band is required. Measurement is often required.
At the time of measurement, there are not a few cases where the laser vibration displacement measuring device is used in combination with another device capable of measuring low-speed vibration, and it has been unavoidable that a large measurement and inspection cost is imposed.

In the measurement of a precise actuator,
A high position / displacement resolution and a wide measurement range were required, and the measurement range had to be divided as necessary to perform multiple measurements.

[0008]

According to the laser vibration displacement measuring device of the present invention, a quadrature demodulator, a phase processing circuit, an adding circuit are used instead of the F / V converter and the integrator in the conventional laser vibration displacement measuring device. By providing a circuit configuration with
The difficulty of high-accuracy measurement when the object to be measured vibrates at low speed has been eliminated.

The quadrature demodulator converts a signal obtained by the photoelectric converter by performing synchronous detection into two components, a component having the same phase as the signal of the beat frequency oscillator and a component having a phase advanced by 90 degrees with respect to the phase. The output is decomposed (the former is referred to as an I component and the latter is referred to as a Q component). That is, the quadrature demodulator converts the input signal on the time base into one point on the IQ coordinate plane on the phase base. I obtained by the quadrature demodulator
The component / Q component is converted into a length (displacement) by the phase processing circuit. Here, the length (displacement) output from the phase processing circuit is proportional to the inverse tangent of the ratio between the Q component and the I component in the quadrature demodulator, and is from the first quadrant to the fourth quadrant on the IQ coordinate plane. Since one rotation of 360 degrees is half the wavelength of the measuring light used, it can be easily converted to a length.

Further, the rotation number of this phase is detected, and the corresponding length and the displacement amount based on the currently obtained phase angle are added by an adder circuit. It becomes measurable. The accuracy of the above configuration is as follows. Considering that the variation on the IQ coordinate plane due to the internal noise of the demodulator is at most about 5 degrees in angle conversion, for example, a red laser beam having a wavelength of 632.8 nm is used. When used, 10 nm (= 316.2 nm / 360 °)
× 5 °) or less.

By taking the above measures, the displacement can be measured with high accuracy in a wide measurement frequency band including the displacement close to the stationary state and in a wide measurement range.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a laser vibration displacement measuring apparatus according to the present invention will be described below with reference to the drawings. In FIG. 1, a laser vibration displacement measuring device 1 of the present invention has an output of 2 m.
A red He-Ne laser oscillator 2 having a wavelength of W and a wavelength of 632.8 nm was used as a light source. The light wave output from the He-Ne laser oscillation device 2 is split into two directions by the beam splitter 3a. On the other hand, the frequency of light is shifted by the signal frequency of the beat frequency oscillator 7, for example, 10.5 MHz, by the acousto-optic converter 4 (AOM) using the change in the refractive index due to the photoelastic effect, Through the splitter (half mirror) 3c, the photoelectric converter 6,
Specifically, it is optically adjusted to irradiate an avalanche photodiode. The other light wave is applied to the device under test 8 via a beam splitter (half mirror) 3b and is reflected by the device 8 to be measured. The reflected light is transmitted from the beam splitter (half mirror) 3b via a mirror 5 to a photoelectric converter. 6 is optically designed.

At this time, the DUT 8 has a frequency of 20 Hz,
The amplitude level was about 0.5 μm. The reflected light has an optical path difference (a constant optical path difference + twice the displacement of the device under test) with respect to the reference light from the red He-Ne laser oscillation device 2 which is the light source, and therefore has a phase difference corresponding thereto. . The phase difference includes information on the position / displacement of the device under test 8. In the photoelectric converter 6, as a result of the reflected light from the device under test 8 and the frequency-shifted reference light overlapping, interference occurs to generate a beat. Moreover, the phase difference between the reflected light and the phase difference between the beat component and the signal of the beat frequency oscillator 7 correspond to each other, and the beat component is converted into an electric signal by the photoelectric converter 6 and the beat frequency oscillator 7 The displacement of the DUT 8 can be calculated by calculating the phase difference from the signal of FIG. Hereinafter, the demodulation portion will be described in detail.

The output of the photoelectric converter 6 is applied to a signal switch 9. The other input of the signal switch 9 is connected to a calibration oscillator 10 that oscillates at a frequency slightly different from the frequency of the beat frequency oscillator 7, and the signal of the calibration oscillator 10 is sent to the subsequent stage at the time of adjustment before measurement. The output of the signal switch 9 is
Since the output level of the photoelectric converter 6 is generally weak,
The signal is amplified by the amplifier 11 to a level at which demodulation is possible. The output of the amplifier 11 is connected to the quadrature demodulator 12. FIG. 2 shows the configuration of the quadrature demodulator 12. The quadrature demodulator 12 is composed of two frequency mixers 15a, 15a having a small characteristic variation.
b, an in-phase distributor 16 and a 90-degree distributor 17. The reference signal c from the beat frequency oscillator 7 is set to 9
One output from the 90-degree distributor 17 is input to the 0-degree distributor 17, and is applied to the frequency mixer 15a, and the other output whose phase is advanced by 90 degrees compared to the output is applied to the frequency mixer 15b. The output of the photoelectric converter 6 is connected to the amplifier 11
The beat signal d amplified in the step (1) is supplied to the in-phase distributor 16, divided into two, and supplied to the frequency mixers 15a and 15b. Quadrature demodulation was performed by these configurations. Here, the I component signal e obtained from the frequency mixer 15a is a value proportional to the inner product of the phase component of the beat signal d on the real axis on the IQ coordinate plane, and the Q component signal obtained from the frequency mixer 15b. f uses a signal whose phase is advanced by 90 ° with respect to the signal applied from the 90-degree distributor 17 to the frequency mixer 15a.
-A value proportional to the inner product on the imaginary axis on the Q coordinate plane. The output of the quadrature demodulator 12 is applied to a phase processing circuit 13. The configuration and operation of the phase processing circuit 13 will be described with reference to FIG.

The phase processing circuit 13 first converts the I-component signal e and the Q-component signal f into analog signal voltages, and converts each signal into an A / D converter 18 for the purpose of performing the subsequent processing stably.
The digital signal is converted into a digital signal using the signals a and 18b, and thereafter, digital processing is performed. Since the I-component signal e and the Q-component signal f contain a residual DC offset voltage, the outputs of the A / D converters 18a and 18b are connected to adders 19a and 19b, respectively, in order to cancel the offset. The data is added to the offset cancel data supplied from 14. Thereby, the adders 19a, 19b
The offset is removed from the output of. Next, adder 1
The outputs of 9a and 19b perform level adjustment and balance adjustment of I signal data and Q signal data by multipliers 20a and 20b.

These adjustments will be described with reference to the IQ plan view of FIG. FIG. 4A shows a state in which the adjustment is completed. The trajectories of the I component and the Q component are perfect circles, and the center of the circle coincides with the origin. FIG. 4B shows a state before the adjustment, in which the centers of the trajectories of the I component and the Q component are shifted in the plus direction of the I axis, and shifted in the minus direction in the Q axis direction. These shifts are corrected by the adders 19a and 19b. When the trajectory is elliptical and there is a difference between the diameter in the I-axis direction and the diameter in the Q-axis direction, correction is performed by the multipliers 20a and 20b.
In order to specifically calculate the offset cancellation data, the signal of the microcomputer 14 is used to calculate the offset cancel data.
Is stopped, the beat signal d, which is an input signal to the in-phase distributor 16, is set to zero, and the microcomputer 14 designates 1 times as a multiplication coefficient of the multipliers 20a and 20b, and outputs the outputs of the multipliers 20a and 20b. The microcomputer 14 takes in the data and calculates the complement of this value to obtain offset cancel data. Next, the multipliers 20a and 20b
Is calculated by slightly moving the DUT 8 in the adjustment mode state before the measurement.
The output locus of 0b is analyzed to determine whether the respective PP (peak-to-peak) values of the I-component and Q-component changes are within a specified value.
4, the gain of the amplifier 11 is changed so as to be within a specified value.

On the other hand, when the I-component and Q-component PP (peak-to-peak) values are within specified values, the gain of the signal line of the lower one is adjusted to balance the I-component and Q-component. To increase. Now, when the I component is low, an operation of (multiplication coefficient of the I component after correction) = (multiplication coefficient of the I component before correction) × (PP value of the Q component) / (PP value of the I component) is performed. This corrected multiplication coefficient value is sent to the multiplier 20a. When the DUT 8 is slightly moved in the adjustment mode state, the balance between the maximum value and the minimum value of the output (plus / minus) as described with reference to FIG. It is possible to calculate a correction value from (balance). In the embodiment of FIG. 1, a signal switch 9 and a calibration oscillator 10 are prepared as practical means for obtaining the multiplication coefficients of the multipliers 20a and 20b. At the time of adjustment, the output of the signal switch 9 is switched to the side of the calibration oscillator 10 in accordance with an instruction from the microcomputer 14, amplified by the amplifier 11, and then input to the in-phase distributor 16.
As a result, the I-component signal e and the Q-component signal f change in the cycle of the frequency difference between the beat frequency oscillator 7 and the calibration oscillator 10, and the locus shown in FIG. 4B is obtained, and the correction value is calculated. Can be.

Next, the outputs of the multipliers 20a and 20b are xy-
to the θ converter 21. Here, the arc tangent of the ratio of the Q component and the I component is obtained as described above. Here, the data from the multipliers 20a and 20b are used as input data by using a ROM in which a conversion table calculated in advance is written. Used as an address, and the ROM output data
It is configured to be displaced. The xy-θ converter 21 may be a combination of a coarse ROM table and an interpolation calculator. The output of the xy-θ converter 21 is a multiplier 22
Is multiplied by a multiplication coefficient corresponding to the setting of the measurement range according to the designation of the microcomputer 14. The multiplier 22 is not a complete multiplier, but can be adapted only by a shift operation. An adder 23 is connected to the output of the multiplier 22 to expand the measurement range. The sub CPU in the microcomputer 14 monitors the output of the xy-θ converter 21 and analyzes how the phase changes from around 0 ° to around 360 °, and displaces each time the phase changes from 360 ° to 0 °. A length corresponding to a half wavelength is integrated as an addition value.
Conversely, when the phase changes from 0 ° to 360 °, the phase is subtracted by 波長 wavelength. The displacement addition value thus obtained is sent from the microcomputer 14 to the adder 23, added to the output of the xy-θ converter 21, and taken out as the final displacement signal a. The above operation enables highly accurate displacement measurement.

Next, the configuration of a laser vibration displacement measuring device 24 according to another embodiment of the present invention will be described with reference to the block diagram of FIG. Blocks having the same functions as the blocks described so far are given the same numbers. Only the differences from the embodiment of FIG. 1 will be described. A frequency converter 26 is provided at the output of a first local oscillator 25 (for example, 10 MHz) used for the same purpose as the beat frequency oscillator 7, and a second local oscillator 27 (for example, 3 MHz) is provided at the other input.
z) and the BP connected to the output of the frequency converter 26
A 13 MHz signal is extracted from F (bandpass filter). The 13 MHz signal and the signal from the amplifier 11 are added to the frequency converter 29 to obtain a measurement signal near 3 MHz. A second amplifier 30 is connected to the output of the frequency converter 29, and this output is connected to the quadrature demodulator 12. As the other reference input of the quadrature demodulator 12, a 3 MHz signal of the second local oscillator 27 is used.

With such a configuration, synchronous detection becomes possible as in the embodiment of FIG. 1, and a displacement output can be obtained. In the embodiment shown in FIG. 1, when the reflected light is extremely weak, it is necessary to increase the amplification degree of the amplifier 11, and the oscillation is likely to occur and the oscillation becomes unstable. In the embodiment of FIG. 5, the amplifier 11 and the second amplifier 30 having an appropriate amplification degree are provided before and after the frequency converter 29, and the coupling between the respective amplifiers does not cause much problem, so that the total amplification degree is increased. Measurement accuracy when reflected light is extremely weak. In addition, the output of the frequency mixer 29 can be set to a low frequency, so that a quadrature demodulator for digital processing can be adopted.
A more stable output can be obtained.

In the configuration described so far, the detailed circuit of each block or the separation between analog processing and digital processing is not limited to the above description, and other configurations can be considered. Are included.

[0022]

According to the laser vibration displacement measuring apparatus of the present invention having the above-described configuration, highly accurate displacement measurement in a wide measuring frequency band including an extremely slow displacement of an object to be measured in an almost stationary state can be performed. It is possible, and moreover, it is possible to measure over a wide measuring range. In addition, in the configuration having the frequency converter, in addition to such an effect, stable measurement can be performed even when the reflected light is extremely weak. For this reason, in the case of measurement, the number of cases in which measurement is performed using a laser vibration displacement measuring device in combination with another conventional device capable of measuring low-speed vibration is reduced, and measurement and inspection costs can be reduced. The industrial significance and social contribution of the present invention are extremely large.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a laser vibration displacement measuring device according to the present invention.

FIG. 2 is a block diagram of a quadrature demodulator in the laser vibration displacement measuring device of the present invention.

FIG. 3 is a block diagram of a phase processing circuit in the laser vibration displacement measuring device of the present invention.

FIG. 4 is an IQ plan view for explaining a method of adjusting a phase processing circuit according to the present invention.

FIG. 5 is a block diagram showing another embodiment of the laser vibration displacement measuring device of the present invention.

FIG. 6 is a block diagram of a conventional laser vibration displacement measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser vibration displacement measuring device of the present invention 2 Laser oscillation device 3a, 3b, 3c Beam splitter 4 Acousto-optic converter 5 Mirror 6 Photoelectric converter 7 Beat frequency oscillator 8 DUT 9 Signal switch F / V converter 10 Calibration Oscillator Integrator 11 Amplifier 12 Quadrature demodulator 13 Phase processing circuit 14 Microcomputer 15a, 15b Frequency mixer 16 In-phase distributor 17 90-degree distributor 18a, 18b A / D converter 19a, 19b Adder 20a, 20b Multiplier 21 XY-θ converter 22 Multiplier 23 Adder 24 Laser vibration displacement measuring device of the present invention 25 First local oscillator 26, 29 Frequency converter 27 Second local oscillator 28 BPF (bandpass filter) 30 Second amplifier 31 Conventional Laser vibration displacement measuring device 32 Signal switch 33 F / V converter 34 Minute unit

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshio Inakoshi 1-8 Nakase, Mihama-ku, Chiba City, Chiba Pref. A) JP-A-5-100663 (JP, A) JP-A-8-219868 (JP, A) JP-A-5-340952 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) G01H 9/00

Claims (3)

(57) [Claims] 1. A laser oscillation device for oscillating a laser beam as a measurement medium for measuring a vibration displacement of an object to be measured, a beam splitter for dispersing reference light and light reflected from the object to be measured. An acousto-optic converter for shifting the frequency of the reference light, a beat frequency oscillator for applying a constant frequency to the acousto-optic converter, and a photoelectric conversion for extracting a voltage corresponding to the amplitude of the light obtained by combining these lights. In a laser vibration displacement measuring device provided with a demodulator and a demodulator for extracting speed or displacement information from a signal obtained by photoelectric conversion, the demodulator is configured to amplify at least a signal obtained by the photoelectric converter. An amplifier, a quadrature demodulator for decomposing the amplified signal into quadrature components by synchronous detection, and a phase for converting quadrature components output from the quadrature demodulator into displacements A laser vibration displacement measuring device comprising a processing circuit. 2. The laser vibration displacement measuring device according to claim 1, further comprising an adder provided after the phase processing circuit for expanding a measurement range. 3. The laser vibration displacement measuring apparatus according to claim 1, wherein a second amplifier is provided before the quadrature demodulator, and a frequency converter is further provided before the second amplifier.