JP7278979B2 - NON-CONTACT VIBRATION MEASURING DEVICE AND NON-CONTACT VIBRATION MEASURING METHOD - Google Patents

Description

An embodiment of the present invention relates to a non-contact vibration measuring device and a non-contact vibration measuring method.

Ultrasonic measurement methods using lasers, so-called laser ultrasonic methods, have traditionally been limited to laboratory measurements, but the development of high-power receiving laser light sources and interference measurement devices that are resistant to rough surfaces has begun. As a result, it is rapidly being applied to industrial sites. Its greatest strength lies in its ability to measure without contact. Therefore, it is expected to be applied to objects that cannot be immersed in a medium such as water.

On the other hand, due to the characteristics of using laser interferometry for receiving ultrasonic waves, the apparatus involved in receiving ultrasonic waves is large and expensive. Moreover, the measurement itself is unstable, and it is necessary to improve the stability of the light source and the interferometer itself. These problems have hindered their widespread use.

In order to solve the above problems, various efforts have been made to make the laser ultrasonic method robust. In order to reduce the speckle noise generated by the surface unevenness of the measurement object, we used an array of light-receiving diodes in the interferometer, used a Fabry-Perot interferometer in which the reflected light self-interferences, and used a fractured surface between the reflected light and the reference light. By introducing a crystal with a photorefractive effect in the middle of the array, stabilization of sensitivity has achieved a certain effect. However, it was still necessary to use a stabilized large-sized laser light source in order to increase the coherency of the originally used laser light, or to construct a table-top size interferometer.

As a different approach, there is a technology that irradiates a target with a laser generated by a thin laser crystal in a microchip, returns the reflected light to the crystal of the microchip laser, and measures particles from the disturbance of the generated laser light. Proposed. This eliminates the need to use an interferometer separately from the laser, and allows the use of an inexpensive light source. However, this technology is a particle characteristic device for measuring the frequency fluctuation of received light, and in order to stably measure the frequency, it is practical to insert a photoacoustic modulation element in front of the beam splitter and the measurement target. This is a required item. Therefore, the present technology is insufficient to measure vibrations in the ultrasonic band, and redundant device configurations are inevitable.

Patent No. 6050619

C.B. Scruby and L. E. Drain, Laser Ultrasonic: Techniques and Applications (Adam Hilger, Bristol, 1990)

Based on the above-mentioned known technology, the object of the present invention is to provide a non-contact vibration measuring device and a non-contact vibration measuring method that can measure ultrasonic vibration with a low-cost device configuration without using a photoacoustic modulator or the like. to do.

A non-contact vibration measuring device according to an embodiment includes a light source, a laser oscillator that irradiates a surface of an object to be measured with a light source laser beam output from the light source as a seed, and a laser beam at a predetermined ratio. a branching beam splitter, the oscillation laser beam split by the beam splitter, and the modulated oscillation laser beam modulated by the scattered feedback laser beam from the surface of the object to be measured to the laser oscillator and split by the beam splitter a photodetector that receives light and converts it into an electrical received signal; and a signal processor that analyzes the received signal, which is the intensity of the oscillating laser light or the modulated oscillating laser light converted by the photodetector, The signal processing section has a frequency filter that excludes the natural frequency of the oscillation laser light from the laser oscillator from the received signal.

The figure which shows the structure of the non-contact vibration measuring device which concerns on 1st Embodiment. A graph showing an example of frequency distribution of received signal strength and received signal fluctuation. A graph showing an example of frequency distribution of received signal strength and received signal fluctuation. Graphs showing example filter bandwidths and example received signals. The figure which shows the structure of the non-contact vibration measuring device which concerns on 2nd Embodiment. FIG. 4 is a diagram for explaining an example when an ultrasonic signal is added; FIG. 5 is a diagram for explaining another example when an ultrasonic signal is added; FIG. 2 is a diagram for explaining the configuration of a non-contact vibration measuring device to which a scanning mechanism is added; FIG. 2 is a diagram for explaining a configuration when performing ultrasonic flaw detection for defect detection;

Hereinafter, a non-contact vibration measuring device and a non-contact vibration measuring method according to embodiments will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram schematically showing the configuration of the non-contact vibration measuring device according to the first embodiment. Incidentally, in FIG. 1, the optical paths that should be drawn coaxially may be drawn in parallel for ease of explanation.

The basic configuration includes a light source 1 for oscillating a light source laser beam 10 and a laser oscillator for oscillating an oscillation laser beam 11 that irradiates the surface of an object 21 to be measured using the light source laser beam 10 output from the light source 1 as a seed. 2 receives the branched oscillating laser beam 11 and the modulated oscillating laser beam 13 modulated by the scattered feedback laser beam 12 from the surface of the object 21 to be measured to the laser oscillator 2 and converts it into a received signal 14 which is a voltage signal. A photodetector 3, a beam splitter 6 for splitting the oscillating laser beam 11, the modulated oscillating laser beam 13, and the scattered feedback laser beam 12 at a predetermined ratio, the oscillating laser beam 11 converted by the photodetector 3, and the modulated oscillating laser. A signal processing unit 4 for analyzing a received signal 14 which is the intensity of either or both of the lights 13 is provided.

The signal processing unit 4 has a frequency filter that excludes from the received signal 14 a signal having a frequency near the natural frequency ω of the laser light defined with the material and crystal thickness of the laser oscillator that are grasped in advance as the main parameters. 5. The frequency filter 5 may be digital processing or analog processing, may be used in combination, or may be combined with an amplifier. For example, in the case of filtering by analog processing, it may be provided before the signal processing section 4 .

Here, the frequency filter 5 for excluding a signal having a frequency near the natural frequency ω of the laser light from the received signal 14 includes the second harmonic 2ω, the third harmonic 3ω, and the natural frequency ω of the received signal 14. A bandpass filter that selectively transmits one or more of the higher harmonic components, such as the nth harmonic nω, can be used. Signal processing and recording such as digitizing the received signal, applying a frequency filter or controlling the filter band, and processing such as spectral analysis of the received signal are performed by the signal processing section 4 provided in the overall control section 8 . The overall control unit 8 has a display unit that displays waveforms, conditions, etc., a user interface such as a mouse, keyboard, and touch panel, and a display unit that displays measurement information such as received signal waveforms, received signal spectra, and filter band values. good too.

As shown in FIG. 1, a light source laser beam 10 emitted from a light source 1 is incident on a laser oscillator 2, and the laser oscillator 2 generates an oscillation laser beam 11. As shown in FIG. The oscillation laser beam 11 is split at a predetermined ratio by the beam splitter 6 , one of which irradiates the surface of the object 21 to be measured and the other of which irradiates the photodetector 3 . The oscillation laser beam reflected by the surface of the object 21 to be measured returns to the beam splitter 6 again as the scattered feedback laser beam 12 , and the component of the scattered feedback laser beam 12 transmitted from the beam splitter 6 returns to the laser oscillator 2 . Part of the scattered feedback laser light 12 reaches the light blocking mechanism from the beam splitter 6 .

When the scattered feedback laser beam 12 is modulated, the laser oscillator 2 to which the scattered feedback laser beam 12 recurs oscillates as a modulated oscillation laser beam 13 in which the natural vibration of the oscillation laser beam 11 is multiplied by another frequency band. . The modulated oscillation laser light 13 is passed through the beam splitter 6 and converted into a reception signal having a voltage waveform by the photodetector 3 .

In the non-contact vibration measuring device having the above configuration, the light source laser beam 10 emitted from the light source 1 includes typical diode lasers, lasers such as He—Ne, lasers such as YAG, and fiber lasers. Here, the material is not limited to anything, and it is preferable to use the material most compatible with the laser oscillator 2, which will be described later.

As the laser oscillator 2 for generating the oscillating laser light 11, it is preferable to use a solid-state laser. Various media can be used as the laser oscillator 2. For example, Nd: _YVO4 , Nd:YAG, TM: _YVO4 , TM:YAG, Yb: _YVO4 , Yb:YAG, Ti:sapphire, etc. are available. It is presumed that it is suitable to use a microchip with a crystal thickness (resonator thickness) of several millimeters. The thickness of the crystal plate is preferably about 0.05 mm to 5 mm, more preferably about 0.5 mm to 2 mm. When the crystal thickness is thin, it becomes sensitive to the modulated scattered feedback laser light 12, but when it is too thin, the physical strength becomes insufficient, for example, the crystal is damaged by heat. On the other hand, if the crystal thickness is increased, the oscillation becomes stable, but it becomes insensitive to the modulated scattered feedback laser beam 12, and vibration measurement cannot be performed with good sensitivity. For example, when Nd:YVO ₄ is used as the laser oscillator 2, the wavelength of the light source laser light 10 is preferably around 808 nm, and the light source 1 is selected accordingly. Of course, combinations other than those exemplified here may be used as long as they generate oscillation laser light 11 .

The beam splitter 6 may be a half mirror or the like that splits the light at a constant rate without depending on polarization, or a polarization beam splitter (polarizer) that performs transmission and reflection according to a certain phase. It may be branched. When a polarizer is used, a wave plate of λ/2 or λ/4 that changes phase information may be combined and inserted as appropriate before or after the polarizer.

The object to be measured 21 is applicable to objects other than those with very high absorption efficiency that do not reflect the oscillation laser beam 11, such as black bodies, or objects such as coarse fibers in which the oscillation laser beam 11 does not exhibit a clear reflection behavior. It is possible, and as the types of materials, materials through which ultrasonic waves propagate, such as metals, composite materials, resins, concrete, and liquids, are assumed.

If the surface of the object to be measured 21 is in a steady state, the oscillation laser beam 11 irradiated to the surface of the object to be measured 21 is reflected as it is and returns to the laser oscillator 2 as the scattered feedback laser beam 12 as it is. . Here, if the surface of the object 21 to be measured is vibrating at a high speed as typified by ultrasonic waves or the like, or if vibration occurs in the optical path of the oscillation laser beam 11 or scattered feedback laser beam 12, the vibration produces a scattered feedback laser beam 12 whose wavelength and phase are changed with respect to the steady-state oscillation laser beam 11 .

When the scattered feedback laser beam 12 is incident on the oscillation portion of the laser oscillator 2 for the oscillation laser beam, the oscillation laser beam 11 is changed. If the scattered feedback laser beam 12 is not modulated, the intensity of the oscillation laser beam 11 will only oscillate around the natural frequency ω of the laser beam, as shown in FIG. 2(a). If the scattered feedback laser beam 12 is modulated in some way, the oscillating laser beam 11 becomes the modulated oscillating laser beam 13, and in the time period when the modulation occurs (for example, in the case of ultrasonic vibration in the MHz band, about several μs) , a frequency component other than the natural frequency ω is generated. The natural frequency ω is defined using the material and crystal thickness of the laser oscillator 2 as main parameters. This natural frequency can also be determined by actual measurement, as shown in FIG. 2(b). The natural frequency can also be known from information such as the material forming the laser oscillator 2 and the crystal thickness. Although FIG. 2B shows the case where the natural frequency ω is in the MHz band, this is only an example.

Here, as an example, the different frequency components are, as shown in FIG. (generally, nω, which is the nth harmonic of the oscillator's natural frequency).

As shown in FIG. 4(a), by providing a band-pass filter that selectively transmits this high-order harmonic component as a frequency filter 5 that excludes the natural frequency of the oscillating laser light from the received signal, As shown in FIG. 4B, vibration information (vibration occurrence time and intensity information) can be obtained. Since the vibration information obtained here is obtained from changes in the natural frequency of the oscillation laser, it may have a value different from the frequency at which the surface of the object to be measured 21 actually vibrates. For example, if the eigenfrequency ω of the oscillator is 2 MHz and a pulse vibration of 3 MHz is generated on the surface of the object 21 to be measured, the reception signals of the modulated oscillation laser beam 13 obtained by the vibration are ω, 2ω, 3ω . has a peak in the frequency band of Therefore, if a band-pass filter is provided around 4 MHz, which is 2ω, for example, the waveform after filter processing will be a pulse oscillation centered around 4 MHz. In addition to the above vibration information (vibration occurrence time and intensity information), it is possible to obtain information on the vibration frequency by investigating the correlation between the vibration frequency and the obtained signal in advance. There is

Here, in order to efficiently transmit the light source laser beam 10, the oscillation laser beam 11, the scattered feedback laser beam 12, and the modulated oscillation laser beam 13 to their subsequent stages, one or more condensing units are provided at one or more locations for each. 7 may be provided. FIG. 1 shows an example in which a condenser 7 is provided between the beam splitter 6 and the photodetector 3 . The light condensing unit 7 may be a combination of general lenses and mirrors, or may be separately customized, such as an aspherical mirror or lens, which can obtain high efficiency in a predetermined system. Also, the transmission does not necessarily have to be spatial transmission, and may be configured to pass through a fiber on the way.

With the above configuration, it is possible to construct a system capable of non-contact vibration measurement without using a separate laser interferometer.

(Second embodiment)
Next, a second embodiment will be described with reference to FIGS. 5-9. In these drawings, portions corresponding to those of the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and overlapping descriptions are omitted.

FIG. 5 is a diagram schematically showing the configuration of a non-contact vibration measuring device according to the second embodiment. In addition, in FIG. 5 (the same applies to FIGS. 8 and 9), optical paths that should be drawn coaxially may be drawn in parallel for ease of explanation.

In the second embodiment, an active ultrasonic measurement and flaw detection technology is configured by applying a vibration excitation source 20, which is an ultrasonic generation source, to the first embodiment, which shows the basic configuration of vibration measurement. be.

The vibration excitation source 20 generates ultrasonic waves U inside or on the surface of the object 21 to be measured. It may be something called a tentacle. In addition, adiabatic expansion/compression by a pulse laser, ultrasonic excitation using ablation, acoustic radiation by a speaker, hammering, blasting, and peening may be used.

As shown in FIG. 6(a), if the vibration excitation source 20 is a probe, the thickness of the piezoelectric element and the applied voltage waveform may produce an ultrasonic wave having a specific center frequency as shown in FIG. 6(b). However, as shown in FIG. 7(a), when ultrasonic excitation is performed by, for example, a pulse laser, a broadband ultrasonic wave is excited as shown in FIG. 7(b). The broadband referred to here means a band sufficiently broader than the natural frequency of the oscillating laser light 11 , such as having a half-value width that is at least twice the half-value width of the eigenfrequency spectrum of the oscillating laser light 11 .

Further, as shown in FIG. 8, a scanning mechanism 23 for scanning one or more of the oscillation excitation source 20, the object to be measured 21, and the irradiation position of the oscillating laser beam 11 (in FIG. 8, the scanning mechanism 23 for scanning the oscillation excitation source 20 is ), measurement at a plurality of positions or synthesis processing (aperture synthesis processing) of signals obtained at a plurality of positions can be performed for visualization. At this time, the scanning mechanism 23 may be a linear motion stage, a rotary stage, a combination thereof, or a multi-axis mechanism such as a robot arm. The scanning mechanism 23 may move the irradiation position of the oscillating laser light and the object to be measured, instead of scanning the vibration excitation source 20 .

The frequency characteristic of the ultrasonic wave U generated from the vibration excitation source 20 is desirably a value apart from the oscillator natural frequency ω. Since a high-order harmonic band is used for filtering the received signal, for example, the frequency is higher than ω as shown in FIG. As in b), having a stable band even at high frequencies may facilitate separation from ω.

The ultrasonic wave U generated from the vibration excitation source 20 is reflected directly or at the back surface or a specific portion of the object 21 to be measured, and reaches the surface of the object 21 to be irradiated with the oscillation laser beam 11 to generate the received signal 14 . measured as At this time, for example, if the directly propagated ultrasonic wave U is measured, surface flaw detection and surface sound velocity measurement of the measured object 21 are possible, and the ultrasonic wave U reflected at the bottom surface of the measured object 21 can be measured. If so, the back surface shape, plate thickness, and bulk wave speed of the object 21 to be measured can be measured. As shown in FIG. 9, if ultrasonic waves U reflected by defects 22 such as specific cracks and voids in the object 21 to be measured can be measured, ultrasonic flaw detection for defect detection is possible.

Further, as shown in FIG. 8, by combining with the scanning mechanism 23, measurement at a plurality of positions or visualization by synthesizing signals obtained at a plurality of positions (aperture synthesis processing) becomes possible. In the position, it is possible to detect the defect 22 which is a blind spot, and the effect of improving the visibility at the time of defect detection can be obtained. Note that the configurations shown in the above embodiments may be used by partially combining each configuration. Further, as described above, when oscillation occurs in the optical path of the oscillation laser beam 11 or the scattered feedback laser beam 12, the oscillation causes the scattered feedback laser beam to change in wavelength and phase with respect to the oscillation laser beam 11 in a steady state. 12, it is possible to detect vibrations such as shock waves in the air or in water, which are the optical paths.

Although several embodiments of the invention have been described above, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

1 light source, 2 laser oscillator, 3 photodetector, 4 signal processor, 5 frequency filter, 6 beam splitter, 7 condenser, 8 overall controller , 10 Light source laser beam 11 Oscillation laser beam 12 Scattered feedback laser beam 13 Modulated oscillation laser beam 14 Received signal 20 Vibration excitation source 21 Object to be measured , 22 Defect, 23 Scanning mechanism.

Claims (9)

a light source;
a laser oscillator that uses the light source laser light output from the light source as a seed and oscillates the oscillation laser light that irradiates the surface of the object to be measured;
a beam splitter that splits laser light into a predetermined ratio;
receiving and electrically receiving the oscillating laser light split by the beam splitter and the modulated oscillating laser light split by the beam splitter after being modulated by the scattered feedback laser light from the surface of the object to be measured to the laser oscillator; a photodetector that converts into a signal;
a signal processing unit for analyzing the received signal, which is the intensity of the oscillating laser light or the modulated oscillating laser light converted by the photodetector;
The non-contact vibration measuring device, wherein the signal processing unit has a frequency filter that excludes a signal corresponding to the natural frequency of the oscillation laser light from the laser oscillator from the received signal. The frequency filter has a function of selecting and transmitting one or more of high-order harmonic components such as second-order harmonics or third-order harmonics of the natural frequency from the received signal. Item 1. The non-contact vibration measuring device according to item 1. 3. The apparatus according to claim 1, further comprising a vibration excitation source that vibrates the object to be measured, wherein the center frequency of the vibration excited by the vibration excitation source is in a band different from the natural frequency. A non-contact vibration measuring device as described. 3. The apparatus according to claim 1, further comprising a vibration excitation source that vibrates the object to be measured, wherein the frequency of vibration excited by the vibration excitation source has a broadband spectrum including the natural frequency. Contact vibration measuring device. 5. The non-contact vibration measuring device according to claim 3, further comprising a scanning mechanism for moving said vibration excitation source. Propagating the vibration excited from the vibration excitation source to the inside or surface of the object to be measured, measuring the vibration from the point to be measured in the object to be measured, and measuring the thickness or shape of the object to be measured 6. The non-contact vibration measuring device according to any one of claims 3 to 5, wherein the non-contact vibration measuring device is used for detecting defects. The non-contact vibration measuring device according to any one of claims 1 to 6, further comprising a scanning mechanism for moving one or more of the irradiation position of the oscillation laser beam and the object to be measured. a step of oscillating a laser beam emitted from a light source to irradiate a surface of an object to be measured with a laser oscillator using a light source laser beam as a seed;
a step of irradiating the surface of the object to be measured with one of the oscillation laser beams split by the beam splitter;
a step of receiving the modulated oscillation laser beam modulated by the scattered feedback laser beam from the surface of the object to be measured to the laser oscillator and split by the beam splitter, and converting the modulated oscillation laser beam into an electrical received signal;
A non-contact vibration measuring method comprising the step of excluding from the received signal a signal corresponding to the natural frequency of the oscillating laser light from the laser oscillator. Propagating vibration excited from a vibration excitation source to the inside or surface of the object to be measured, measuring vibration from a point to be measured in the object to be measured, and measuring the thickness or shape of the object to be measured; or used for defect detection.

Images