Non-contact vibration measuring device and non-contact vibration measuring method

Abstract

To provide a contactless oscillation measurement device and a contactless oscillation measurement method that can extract desired information from an obtained reception signal.SOLUTION: A contactless oscillation measurement device comprises: a laser oscillator that oscillates oscillation laser light with which a surface of an object to be measured is irradiated with light-source laser light as a seed; a beam splitter; a light detection unit that receives oscillation laser light branched by the beam splitter and modulation oscillation laser light modulated by scattering feedback laser light to the laser oscillator from the surface of the object to be measured and branched by the beam splitter, and converts the oscillation laser light and the modulation oscillation laser light to an electric signal; and a signal record unit that records a reception signal serving as intensity of the oscillation laser light or the modulation oscillation laser light converted by the light detection unit. Within time from a signal recording start to a signal recording end, delay time of at least two arbitrary values and a time gate of an arbitrary width provided for every delay time are provided, and the reception signal acquired at respective time gates is individually recorded.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a non-contact vibration measuring device and a non-contact vibration measuring method. [Background technology]

[0002] Laser-based measurement technology is attracting attention as a method for remote and non-destructive inspection in a variety of fields, from concrete infrastructure and manufactured products involving welding to living organisms. Ultrasonic measurement methods using lasers, known as laser ultrasonic methods, have traditionally been limited to laboratory measurements, but with the development of high-power receiving laser light sources and interferometric measurement devices that are resistant to rough surfaces, their application in industrial settings is rapidly expanding. For example, in-process welding inspection, in which a laser is irradiated onto a high-temperature weld bead during welding to detect any defects that occur on the spot, has been put into practical use.

[0003] The greatest strength of laser ultrasound is that it allows for non-contact measurement, and it is expected to be applied to objects that are difficult to contact with a probe, such as objects that are too fragile, small, narrow, or hot to touch, or objects that cannot be immersed in a medium such as water due to the impact on performance or the size of the object.

[0004] However, due to the nature of using laser interferometry to receive ultrasound, the equipment required to receive it is large and expensive. Furthermore, the measurement itself is unstable, requiring improvements to the stability of the light source and interferometer. These issues have hindered widespread adoption. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5651533 [Patent Document 2] Patent No. 6050619 Summary of the Invention [Problem to be solved by the invention]

[0006] To overcome the above-mentioned challenges, various efforts have been made to make the laser ultrasound method more robust. For example, to reduce speckle noise caused by the surface irregularities of the measurement target, the light-receiving diodes in the interferometer are arrayed, a Fabry-Perot interferometer is used in which the reflected light undergoes self-interference, or a photorefractive crystal is introduced midway to align the wavefronts of the reflected light and the reference light. These efforts have had some effect in stabilizing sensitivity.

[0007] However, it was still necessary to use a large stabilized laser light source to increase the coherency of the laser light originally used, and to assemble a tabletop-sized interferometer.

[0008] As a different approach, for example, a technology has been proposed in which a laser generated by a thin laser crystal on a microchip is irradiated onto the target, the reflected light is returned to the microchip laser crystal, and particle measurement is performed based on the disturbance of the generated laser light.

[0009] However, the received signal obtained using this method is a mixture of two laser beams: the laser beam generated by the microchip crystal, and the modulated oscillation laser beam that is generated when this laser beam is reflected by the object to be measured and returned to the microchip crystal, and then modulated by the returned laser beam.

[0010] An object of the present invention is to provide a non-contact vibration measuring device and a non-contact vibration measuring method that can extract desired information from the received signal obtained as described above when the signal is affected by changes in conditions such as the surface condition or vibration state of the object to be measured, or the excitation state of the microchip crystal. [Means for solving the problem]

[0011] The non-contact vibration measuring device of the embodiment includes a laser oscillator having a light source, which emits an oscillating laser beam using a light source laser beam output from the light source as a seed to irradiate the surface of an object to be measured; a beam splitter; a photodetector which receives the oscillating laser beam split by the beam splitter and the modulated oscillating laser beam modulated by scattered feedback laser beam from the surface of the object to the laser oscillator and split by the beam splitter, and converts them into an electrical signal; and a signal recording unit which records a received signal which is the intensity of the oscillating laser beam or the modulated oscillating laser beam converted by the photodetector. a signal processing unit for analyzing the recorded received signal; The oscillation laser light and the modulated oscillation laser light have coaxial optical paths and are split by the same beam splitter, and within the time from the start to the end of signal recording, Vibration is applied to the object to be measured by a vibration source, and one or more first time gates are provided after a first delay time from the time when the vibration is applied, and one or more second time gates are provided after a second delay time having a value different from the first delay time, and the received signals acquired at each of the time gates are recorded, and the signal processing unit: The time gates obtained The aforementioned The device is characterized by having a signal frequency characteristic comparison function that compares the frequency characteristics of the received signal, and by comparing the signal when there is no vibration with the signal when there is the influence of vibration, it is possible to evaluate the difference in frequency characteristics depending on whether there is vibration or not. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a non-contact vibration measuring device and a non-contact vibration measuring method that can extract desired information from the received signal when the signal is affected by changes in conditions such as the surface condition or vibration state of the object to be measured, or the excitation state of the microchip crystal. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing a schematic configuration of a non-contact vibration measuring device according to a first embodiment. [Figure 2] 4A and 4B are diagrams showing examples of delay times and time gates in the first embodiment. [Figure 3] 5A and 5B are diagrams showing other examples of delay times and time gates in the first embodiment. [Figure 4] 5A and 5B are diagrams showing other examples of delay times and time gates in the first embodiment. [Figure 5]FIG. 3 is a diagram showing another example of the schematic configuration of the non-contact vibration measuring device according to the first embodiment. [Figure 6] 5A and 5B are diagrams showing examples of delay times, time gates, and signal intensities in the first embodiment. [Figure 7] 6A and 6B are diagrams showing other examples of delay times, time gates, and signal intensities in the first embodiment. [Figure 8] 5A and 5B are diagrams showing other examples of delay times and time gates in the first embodiment. [Figure 9] 6A and 6B are diagrams showing other examples of delay times, time gates, and signal intensities in the first embodiment. [Figure 10] 5A and 5B are diagrams showing examples of delay times and time gate frequencies in the first embodiment. [Figure 11] FIG. 4 is a diagram showing an example of analysis by frequency in the first embodiment. [Figure 12] FIG. 10 is a diagram showing a schematic configuration of a non-contact vibration measuring device according to a second embodiment. [Figure 13] FIG. 10 is a diagram showing another example of the schematic configuration of the non-contact vibration measuring device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a non-contact vibration measuring device and a non-contact vibration measuring method according to an embodiment will be described with reference to the drawings.

[0015] (First embodiment) A non-contact vibration measuring device and a non-contact vibration measuring method according to a first embodiment will now be described. Representative examples are shown in Figures 1 and 2. Note that in these figures, optical paths that should be drawn coaxially may be drawn parallel to each other for ease of explanation.

[0016] As shown in Fig. 1, the non-contact vibration measuring device includes a laser oscillator 2, a light detection unit 3, and a beam splitter 7. The laser oscillator 2 includes a light source 1 for emitting a source laser beam 10, and oscillates an oscillating laser beam 11 that is irradiated onto the surface of an object 21 to be measured using the source laser beam 10 output from the light source 1 as a seed.

[0017] The light detection unit 3 receives the oscillating laser light 11 split by the beam splitter 7 and the modulated oscillating laser light 13 modulated by the scattered feedback laser light 12 from the surface of the object 21 to the laser oscillator 2, and converts them into an electrical signal, a received signal 14. The beam splitter 7 splits the oscillating laser light 11, the modulated oscillating laser light 13, and the scattered feedback laser light 12 at a predetermined ratio.

[0018] The non-contact vibration measuring device also includes a signal recording unit 4, a signal processing unit 5, a signal recording time setting unit 6, and an overall control unit 9. The signal recording unit 4 records a received signal 14, which is the intensity of either or both of the oscillation laser light 11 and the modulated oscillation laser light 13 converted by the light detection unit 3. The signal processing unit 5 processes the received signal 14 recorded in the signal recording unit 4. As will be described later, the signal recording time setting unit 6 sets the signal recording time, including setting two or more arbitrary delay times Tdi and time gates Tgi of arbitrary widths for each delay time, within the time from the start to the end of signal recording. The overall control unit 9 controls the operation of these signal processing systems and the operation of the entire device.

[0019] Here, signal processing such as digitizing the received signal 14, applying a frequency filter, or controlling the filter band width, and recording are performed by the overall control unit 9. The overall control unit 9 may have a display unit that displays waveforms, conditions, etc., and a user interface such as a mouse, keyboard, or touch panel.

[0020] As shown in Fig. 1, light source laser light 10 emitted from light source 1 is incident on laser oscillator 2, which generates oscillating laser light 11. Oscillated laser light 11 is split at a predetermined ratio by beam splitter 7, and one beam is irradiated onto the surface of object 21 to be measured, and the other beam is irradiated onto light detection unit 3.

[0021] The oscillating laser light 11 reflected by the surface of the object to be measured 21 returns to the beam splitter 7 as scattered feedback laser light 12 , and the scattered feedback laser light component transmitted through the beam splitter 7 returns to the laser oscillator 2 .

[0022] When the scattered feedback laser light 12 is returned to the laser oscillator 2, and the scattered feedback laser light 12 is modulated, it is oscillated as modulated oscillation laser light 13, in which the natural frequency of the oscillation laser light 11 is multiplied by another frequency band. This modulated oscillation laser light 13 is converted into a received signal 14, which has a voltage waveform, by the photodetector 3 through the beam splitter 7. In some cases, a photodetector 8 is provided to collect the laser light incident on the photodetector 3.

[0023] In this configuration, examples of the light source laser light 10 emitted from the light source 1 include typical diode lasers, lasers such as He-Ne, lasers such as YAG, fiber lasers, etc. There is no particular limitation here, and it is important to use one that is most compatible with the laser oscillator 2 described below.

[0024] The laser oscillator 2 that generates the oscillating laser light 11 is preferably one that generates a continuous wave using the light source laser light 10 as a seed. Various media can be used, but it is assumed that those that are used in microchips with a crystal plate thickness (resonator thickness) of sub-millimeter to several millimeters, such as Nd:YVO4 or Nd:YAG, are suitable. For example, when Nd:YVO4 is used as the laser oscillator 2, the wavelength of the light source laser light 10 is preferably around 808.8 nm, and the light source 1 is selected accordingly. Of course, combinations other than those exemplified here are also possible as long as they generate the oscillating laser light 11.

[0025] The beam splitter 7 may be a device that splits light at a fixed rate regardless of polarization, such as a half mirror, or a device that splits light into transmission and reflection according to a certain phase, such as a polarizing beam splitter (polarizer).When a polarizer is used, a λ / 2 or λ / 4 wave plate that changes the phase information may be inserted before or after the polarizer as appropriate.

[0026] The object 21 to be measured is assumed to be made of a material such as metal, composite material, or resin. If the surface of the object 21 to be measured is in a steady state, the oscillating laser light 11 is reflected as is and returns to the laser oscillator 2 as scattered feedback laser light 12. If the surface of the object 21 to be measured is vibrating at high speed, as typified by ultrasound, the vibration will generate scattered feedback laser light 12 whose wavelength and phase are changed relative to the oscillating laser light 11 in the steady state.

[0027] Here, the function of the signal recording unit 4 that records the received signal 14, which is the intensity of both or one of the oscillation laser light 11 and modulated oscillation laser light 13 converted by the light detection unit 3, will be described.

[0028] 2 shows a case in which, between signal recording start time Ts and signal recording end time Te, a time gate Tg1 is set after a delay time Td1 from signal recording start time Ts, and a time gate Tg2 is set after a delay time Td2 from signal recording start time Ts, and signals within each time gate are acquired. For example, if the signal acquired at time gate Tg1 contains information about the vibration phenomenon to be measured, information can be obtained about what kind of signal will appear at the time gate Tg2 immediately thereafter. Signal recording by the signal recording unit 4 can be performed by first recording the signal between signal recording start time Ts and signal recording end time Te, and then extracting and re-recording the signals at each time gate Tg1 and Tg2, or by recording only the signals at each time gate Tg1 and Tg2.

[0029] The delay time Tdi and time gate Tgi can be set to any desired value using a separately provided signal recording time setting unit 6, or they can be set by providing a time setting function in the signal recording unit 4. The time can be set by specifying the data acquisition timing in the measurement program or by issuing a trigger from a delay pulse generator. Signal analysis is performed by the signal processing unit 5, but as will be described later, the signal processing unit 5 can also be equipped with a signal strength comparison function and a signal frequency characteristic comparison function to enable more detailed evaluation.

[0030] Figure 2 shows an example in which a signal immediately after a vibration signal is acquired by setting a delay time and a time gate. However, the delay time and time gate can each be set to two or more values ​​and can be set to any value. Therefore, they can be set to any time period between the signal recording start time Ts and the signal recording end time Te.

[0031] Figure 3 shows a case where the second time gate Tg2 is performed immediately before the signal recording end time Te, rather than immediately after recording the vibration signal at time gate Tg1. Figures 2 and 3 show the data acquisition timing for a single signal recording using two time gates. However, as shown in Figure 4, it is also possible to perform repeated measurements two or more times. This can be achieved, for example, by recording signals at each trigger generated at a fixed time interval by a pulse generator or triggered by information input to another measurement sensor, such as a voltage value, exceeding a predetermined threshold. Other methods, such as manually determining the start and end of signal recording, are also possible. When signal recording is repeated, as shown in Figure 3, the signal acquired at Tg2 can be used to check the status of the measurement system before the next recording begins.

[0032] Next, consider a case where measurement is performed by vibrating the object to be measured 21 using the vibration source 20, as shown in Figure 5. A time chart is shown in Figure 6. Here, signal recording starts at the same time as the excitation time Tv, but this is not limited to this; for example, signal recording may start with a delay from the time of excitation. A signal Svi due to vibration generated by the vibration source 20 is acquired using time gate Tg1, and the signal from time gate Tg2 can be used as a background signal (when there is no vibration).

[0033] When vibrations generated by excitation from the excitation source 20 propagate through the object to be measured 21 and are repeatedly measured, Sv may be acquired multiple times as shown in Figure 7. Even when excitation is performed, it is possible to record signals two or more times, as in Figure 4. An example is shown in Figure 8. When excitation is performed, various methods are possible, such as using a trigger from a pulse generator or starting signal recording using the timing of excitation as a trigger.

[0034] Next, we will consider a method for evaluating the characteristics of a signal acquired using a time gate. Up to this point, the components related to signal acquisition include the signal recording unit 4, signal processing unit 5, and signal recording time setting unit 6. The signal processing unit 5 can be given the functions of signal strength comparison and signal frequency characteristic comparison. Each function will be explained below.

[0035] First, we will explain the signal intensity comparison function. When the oscillating laser beam 11 is irradiated onto the object to be measured 21, the amount of scattered feedback laser beam 12 varies depending on the surface condition of the object to be measured 21, i.e., its roughness and shape. If the object to be measured 21 has a surface roughness close to a mirror finish and a flat shape, a high proportion of the scattered feedback laser beam 12 will be specularly reflected compared to the incident oscillating laser beam 11. On the other hand, if the oscillating laser beam 11 is irradiated onto the object to be measured 21 with a rough or curved surface, the beam is more likely to be scattered when reflected, and therefore the amount of scattered feedback laser beam 12 returning in the incident direction will be low.

[0036] Even when vibration is intentionally applied, when the object to be measured 21 itself is vibrating, or when it is vibrating due to an external factor, information about the vibration can be obtained from the modulated oscillation laser light 13. However, the modulated oscillation laser light 13 requires that the scattered feedback laser light 12 is returned to the laser oscillator 2 with a sufficient amount of light, and the signal intensity of the modulated oscillation laser light 13 obtained by the light detection unit 3 changes depending on the increase or decrease of the scattered feedback laser light 12.

[0037] However, as described above, the light detection unit 3 receives the oscillation laser light 11 and the modulated oscillation laser light 13 that are branched by the beam splitter 7, and cannot separate the oscillation laser light 11 and the modulated oscillation laser light 13. Therefore, it is impossible to distinguish between the change in the laser output of the light source 1 and the laser oscillation efficiency of the laser oscillator 2 and the change in the amplitude of the modulated oscillation laser light 13 due to the change in the amount of the scattered return laser light 12.

[0038] FIG. 9 shows an example in which signal recording is performed for each vibration, two time gates are provided within each signal recording time to acquire data, and comparison between the data is performed based on the maximum signal intensity. When measurement is performed while changing the measurement location, the amount of the scattered return laser light 12 may change due to the change in the surface state as described above.

[0039] Here, when comparing the maximum values of the amplitudes (Tg1: I11, I31, In1, Tg2: I12, I32, In2) of the signal intensities at Tg1 and Tg2 of each of the signal recording results (M1, M3, Mn) obtained for three vibrations (time Tv1, Tv3, Tvn) between the same time gates, relationships such as I11 < I31 = In1 and I12 < I32 < In2 can be evaluated. The signal intensity of the time gate Tg2 can be treated as a background that has no relation to the amplitude. By correcting the signal intensity of the time gate Tg1 having amplitude information with the change in this background, for example, it becomes possible to evaluate the signal intensity from which the influence of the change in the surface state of the measurement target 21 is removed. That is, as described above, the signal intensity is I11 < I31 = In1, but if this is corrected with the change in the background, I11 <i31>The background may change due to a change in the surface condition of the object 21 to be measured, as well as a change in the light source 1 or the laser oscillator 2.

[0040] The signal strength can be the maximum amplitude, the average signal strength within the time gate, or the maximum or average signal strength within a more limited time range within the time gate, or other methods of quantifying the strength through statistical processing.In addition to comparing signal strength within the same signal recording (M1, M3, Mn), it is also possible to extract only the signal from time gate Tg2, for example, and monitor the trend of change during measurement.

[0041] Next, we will explain how to perform frequency analysis and comparison on the signals at each time gate. Figure 10 shows an example of frequency characteristic evaluation using Fourier transform on the signals at time gates Tg1 and Tg2 of the signal recording results (M1, M3) of two vibration applications (times Tv1 and Tv3). Time gate Tg1 is the signal during the time affected by vibration, and time gate Tg2 is the signal during the time not affected by vibration. By comparing the two, it is possible to evaluate the difference in frequency characteristics due to the presence or absence of applied vibration.

[0042] Furthermore, by changing the value of the delay time Td2 during measurements, it is possible to determine the time when the vibration effect is eliminated. Furthermore, as shown in Figure 11, it is possible to compare signals not only within the same signal recording time but also with signals generated by different excitations (e.g., comparing Tg1 of M1 with Tg1 of M2), or to compare signals generated using the same or different time gates (e.g., comparing Tg1 of M1 with Tg2 of M2). Because the oscillating laser beam 11 and the modulated oscillating laser beam 13 each have their own frequency characteristics that change depending on the oscillation conditions and the presence or absence of vibration, these functions enable detailed comparisons and are effective in clarifying vibration phenomena. Frequency characteristic evaluation may also be performed in combination with the signal intensity evaluation described above.

[0043] The signal recording time setting for signal evaluation shown in the first embodiment may be set by determining a value in advance before measurement, or it is also possible to set a time gate or the like after measuring data once and evaluate it. Furthermore, when measurements are repeated, it is assumed that measurements will be continued with the same time setting, but the setting value may be changed midway, or a different value may be set for each repetition.

[0044] (Second embodiment) Next, a second embodiment will be described. Here, a case where ultrasonic waves are received in ultrasonic flaw detection will be described. Fig. 12 shows a case where a pulsed laser is irradiated as an ultrasonic excitation source (excitation source 20). In Fig. 12, reference numeral 23 denotes a scanning mechanism that operates the excitation source 20. In the laser ultrasonic method, ultrasonic waves can be generated by irradiating the surface of the object 21 to be measured with a pulsed laser having a pulse width of several nanoseconds.

[0045] Examples of lasers used as pulsed laser light sources include Nd:YAG lasers, CO2 lasers, Er:YAG lasers, titanium sapphire lasers, alexandrite lasers, ruby ​​lasers, dye (dye) lasers, and excimer lasers, and of course other laser light sources are also possible. The laser light source may consist of not just one unit, but two or more units.

[0046] On the ultrasonic wave receiving side, an oscillating laser beam 11 is irradiated onto an object to be measured 21, scattered feedback laser beam 12 is reinjected into the laser oscillator 2, and modulated oscillating laser beam 13 is generated and received by the light detecting unit 3, thereby obtaining a received signal 14 of the ultrasonic wave U. The irradiation position of the pulsed laser can be changed by scanning the irradiation probe, which is the excitation source 20, with a scanning mechanism 23.

[0047] Fig. 13 shows a case where ultrasonic waves are transmitted by a piezoelectric element as an excitation source 20, instead of ultrasonic excitation by a pulsed laser. As in the case of Fig. 12, ultrasonic waves reflected from a defect 22 present inside a test object 21 are received by self-mixing interferometry, making it possible to perform defect detection.

[0048] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0049] 1...light source, 2...laser oscillator, 3...light detection unit, 4...signal recording unit, 5...signal processing unit, 6...signal recording time setting unit, 7...beam splitter, 8...light focusing unit, 9...overall control unit, 10...light source laser light, 11...oscillating laser light, 12...scattered feedback laser light, 13...modulated oscillating laser light, 14...receiving signal, 20...oscillating source, 21...object to be measured, 22...defect, 23...scanning mechanism

Claims

1. a laser oscillator including a light source, which oscillates an oscillation laser beam to be irradiated onto a surface of an object to be measured using a light source laser beam output from the light source as a seed; A beam splitter; a light detection unit that receives the oscillating laser light split by the beam splitter and the modulated oscillating laser light modulated by the scattered feedback laser light from the surface of the object to the laser oscillator and split by the beam splitter, and converts the modulated oscillating laser light into an electric signal; a signal recording unit that records a received signal that is the intensity of the oscillation laser light or modulated oscillation laser light converted by the light detection unit; a signal processing unit for analyzing the recorded received signal; Equipped with the oscillating laser light and the modulated oscillating laser light have coaxial optical paths and are split by the same beam splitter, Vibration is applied to the object under test by a vibration source within a time period from the start of signal recording to the end of signal recording, and one or more first time gates are provided after a first delay time from the time of vibration application, and one or more second time gates are provided after a second delay time having a value different from the first delay time, and the received signals acquired at each of the time gates are recorded; the signal processing unit has a signal frequency characteristic comparison function for comparing the frequency characteristics of the received signal obtained for each time gate, and thereby evaluates the difference in frequency characteristics depending on the presence or absence of applied vibration by comparing a signal during a time when the signal is not subjected to vibration with a signal during a time when the signal is subjected to the influence of vibration; A non-contact vibration measuring device characterized by:

2. In the non-contact vibration measuring device according to claim 1, A non-contact vibration measuring device comprising a signal recording time setting unit for setting the delay time and the time gate.

3. In the non-contact vibration measuring device according to claim 1 or 2, The non-contact vibration measuring device is characterized in that the steps from the start of signal recording to the end of signal recording are repeated.

4. A non-contact vibration measuring device according to any one of claims 1 to 3, a signal strength comparison function for comparing the signal strength of the received signal obtained for each of the time gates;

5. A non-contact vibration measurement method using the non-contact vibration measurement device according to any one of claims 1 to 4, A non-contact vibration measuring method, characterized in that a pulsed laser is used as the vibration source.

6. A non-contact vibration measurement method using the non-contact vibration measurement device according to any one of claims 1 to 4, A non-contact vibration measuring method, characterized in that a piezoelectric element is used as the vibration source.

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