Measurement System

Abstract

One embodiment of the present invention provides a measurement system capable of measuring the three-dimensional shape and vibration of an object by a simple configuration. A measurement system according to one embodiment of the present invention comprises: a laser light source that outputs frequency-modulated continuous wave laser light; a laser scanner that scans an object with the frequency-modulated continuous wave laser light; an interferometer that splits the frequency-modulated continuous wave laser light into reference light and measurement light, and inputs the reference light and reflected light resulting from the measurement light reflected off the object to cause interference therebetween; a shape measurement instrument that measures the three-dimensional shape of the object on the basis of the center frequency of a beat signal obtained through the interference; an FM demodulation instrument that performs FM demodulation on a signal obtained through the interference and detects an FM sideband; and a vibration measurement instrument that measures vibration of the object on the basis of the detected FM sideband.

Description

[Technical Field]

[0001] The present invention relates to a technique for measuring an object using a laser beam. [Background technology]

[0002] [Measurements of social infrastructure structures] Roads and bridges ,to This section explains measurements of "social infrastructure structures" such as tunnels, dams, and buildings, particularly concrete structures. In recent years, the inspection and maintenance of so-called "social infrastructure structures" such as roads, bridges, tunnels, dams, and buildings (understanding the condition of the structures and repairing them accordingly) has become a major social issue. Inspecting these social infrastructure structures requires determining the presence and extent of damage (cracks, lifting, etc.), and for this purpose, the three-dimensional shape and vibration of the objects are measured. Note that "infrastructure" is an abbreviation of "infrastructure." Furthermore, while a "concrete structure" is a structure made using concrete, materials other than concrete, such as rebar or steel frames, may also be used.

[0003] In such concrete structures, "floating" of concrete refers to a state in which the concrete near the surface is losing its integrity with the internal concrete due to continuous cracks inside the concrete or defects during construction that cause vibrations or deformation during use. (https: / / www.tukigata.co.jp / publics / index / 41 / (According to the Tsukigata Corporation website). In this state, cracks form inside the concrete due to corrosion of the rebar, pushing up the surface of the concrete and creating a convex "floating" shape. As stated on the website, concrete with a floating shape will peel off if it continues to deteriorate or is subjected to impact.

[0004] The progression of such lifting and peeling can be divided into, for example, the incubation period, progression period, early acceleration period, late acceleration period, and deterioration period, but it is said that internal deterioration can be detected by tapping by humans starting halfway through the early acceleration period. The early acceleration period is a state in which internal cracks (fissures) and surface deformation and cracks have occurred due to corrosion and expansion of the rebar, and the surface deformation is slight (it is estimated to be a state in which the rebar has risen by about 0.1 to 0.2 mm or more).

[0005] In the past, workers would check the 3D shape and vibration of an object by visual inspection or by tapping, but this type of work takes time and effort, and it can also be difficult to get close to the object.

[0006] In response to such situations, it is conceivable to apply a technology for non-contact measurement of an object using laser light. FIG. 16 is a diagram showing how a laser scanner 700 is used to measure the three-dimensional shape of an object 710. In the example shown in the figure, a convex CV caused by deterioration (internal cracks 714 and corrosion 716) of a rebar 712 is measured from a distance of 5 m. It is also known to measure distance using a frequency-shifted feedback laser (FSF laser) (see, for example, Patent Document 1). Patent Document 1 also describes that the three-dimensional shape can be measured by scanning the object with an FSF laser (repeated distance measurements). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-096383 Summary of the Invention [Problem to be solved by the invention]

[0008] When measuring the 3D shape of an object, if the influence of the shape caused by construction (the original shape may be raised or depressed) is superimposed on the measurement results, there is a possibility of false detection or missed detection. Also, even if damage has occurred, if the extent is slight, it may be missed. For this reason, it may be difficult to thoroughly inspect an object by measuring the 3D shape alone.

[0009] Therefore, it is conceivable to combine 3D shape measurement with non-contact acoustic inspection (vibration measurement). This is because damage can be detected and measured more accurately if the vibrations that cause damage can be measured. Non-contact acoustic inspection works on the same principle as hammering sounds made by workers, and for example, the vibration of an object caused by a vibration sound source (acoustic excitation source) is measured using a laser vibrometer or the like. A conceptual diagram of non-contact acoustic inspection is shown in Figure 17. In the example shown in the figure, the vibration of an object 710 caused by a vibration sound source 730 is measured using a laser scanner vibrometer 720. Since the frequency and intensity of the vibration depend on the degree of damage, the degree of damage can be ascertained by measuring the vibration.

[0010] However, simply combining the above-mentioned three-dimensional laser measurement and non-contact acoustic inspection would result in a large-scale system and increased costs.

[0011] As described above, conventional techniques have not been able to measure the three-dimensional shape and vibration of an object with a simple configuration.

[0012] The present invention has been made in view of the above circumstances, and has an object to provide a measurement system that can measure the three-dimensional shape and vibration of an object with a simple configuration. [Means for solving the problem]

[0013] [Basic concept of the present invention] The inventors of the present application conducted extensive research into the combined use of the above-mentioned three-dimensional shape measurement and non-contact acoustic probing, and discovered that the FSF laser described in Patent Document 1 is a type of FMCW laser (FMCW: Frequency Modulated Continuous Wave laser) and can be used as the light source for a "pseudo-heterodyne" LDV (Laser Doppler Vibrometer). This led to the idea that "by applying this FSF laser or FMCW laser to damage vibration measurement as well, that is, by using a laser light source for both three-dimensional shape measurement and vibration measurement, the system can be simplified" (note that heterodyne LDVs are not suitable for distance measurement or three-dimensional shape measurement). Below, we will explain each aspect of the present invention created based on this idea.

[0014] [Each aspect of the present invention] In order to achieve the above-mentioned object, a measurement system according to a first aspect of the present invention includes a laser light source that outputs a frequency-modulated continuous wave laser beam, a laser scanner that scans an object with the frequency-modulated continuous wave laser beam, an interferometer that splits the frequency-modulated continuous wave laser beam into a reference beam and a measurement beam and causes interference between the reference beam and a light reflected from the object, a shape measuring instrument that measures the three-dimensional shape of the object based on the center frequency of a beat signal obtained by the interference, and a shape measuring instrument that measures the three-dimensional shape of the object based on the center frequency of a beat signal obtained by the interference. beat The device includes an FM demodulator that FM demodulates the signal and detects the FM sideband, and a vibration measuring device that measures the vibration of the object based on the FM sideband obtained by the detection.

[0015] In the first embodiment, the center frequency of the beat signal obtained by interference corresponds to the distance to the point where the laser light is irradiated, so by scanning the object, the distances to multiple points can be determined, and the three-dimensional shape of the object can be measured. On the other hand, the FM sideband corresponds to the vibration frequency of the object, so the center frequency of the beat signal obtained by interference corresponds to the distance to the point where the laser light is irradiated, so the three-dimensional shape of the object can be measured. beat The vibration of the target object can be measured by FM demodulating the signal. "FM" stands for Frequency Modulation.

[0016] As described above, the measurement system according to the first aspect can measure the three-dimensional shape of the object. of In this case, a laser light source that outputs FMCW laser light is used as the light source for 3D shape measurement and the light source for vibration measurement, which prevents the system from becoming too large by simply combining the two systems.

[0017] In this way, the measurement system according to the first aspect can measure the three-dimensional shape and vibration of an object with a simple configuration.

[0018] The three-dimensional shape and vibration can be used to understand the condition of the object (presence or absence of damage, degree of damage, etc.).

[0019] In the first aspect and each of the following aspects, a "frequency modulated continuous wave laser" (hereinafter sometimes referred to as "FMCW laser") is a laser beam that transmits a frequency-modulated continuous wave, and distance can be determined from the frequency difference (beat frequency) between the transmitted wave and the reflected wave. In measurements using frequency modulated continuous wave laser beams, distance resolution is determined by frequency changes.

[0020] In the first embodiment and each of the following embodiments, the three-dimensional shape measurement and the vibration measurement may be performed simultaneously, in parallel, or separately.

[0021] In the first aspect, a vibration source may or may not be used for vibration measurement. Even without excitation from a vibration source, it is possible to measure the natural vibration of the object and normal vibrations caused by use (such as vibrations of roads and bridges where vehicles are constantly running, and vibrations of equipment that operates continuously).

[0022] The measurement system according to the second aspect is the same as that of the first aspect, except that the laser light source outputs frequency-shifted feedback laser light as frequency-modulated continuous-wave laser light. The second aspect defines a specific aspect of a "frequency-modulated continuous-wave laser," and a "frequency-shifted feedback laser" (hereinafter sometimes referred to as an FSF laser) is a laser configured to feed back the output of a frequency shifter (such as first-order diffracted light from an acousto-optic element) to a gain medium, and is a type of frequency-modulated continuous-wave laser.

[0023] The measurement system according to a third aspect is the first or second aspect, further comprising an excitation sound source that irradiates sound onto the object to excite vibration, and the vibration measuring device measures the vibration of the excited object. The third aspect specifies an example of the excitation sound source, and for example, a directional speaker can be used as the excitation sound source.

[0024] The measurement system according to the fourth aspect is the same as that of the third aspect, but further includes an area setting unit that sets a sound irradiation area to which sound is irradiated, and the vibration sound source irradiates sound into the set sound irradiation area. According to the fourth aspect, it is possible to irradiate (excite) sound into a desired area. The area to be irradiated with sound may be a partial area of ​​the object. Furthermore, the area setting unit may set the sound irradiation area based on a user instruction, or may set it independently of a user instruction.

[0025] The measurement system according to the fifth aspect is the fourth aspect, in which the area setting unit extracts candidate areas that are candidates for the sound irradiation area based on the measured three-dimensional shape, and displays the extracted candidate areas on a display device. The fifth aspect defines one aspect of candidate area extraction and display.

[0026] The measurement system according to the sixth aspect is the fifth aspect, in which the region setting unit extracts, as a candidate region, a region where the deviation from design information of the three-dimensional shape of the object and / or previously acquired measurement results of the three-dimensional shape exceeds a standard. The sixth aspect specifically defines one aspect of candidate region extraction. For example, information based on CAD (Computer Aided Design) data of the object can be used as the "design information." In this case, the region setting unit can extract, as a candidate region, a region where the deviation from the design value exceeds a standard. Furthermore, for example, past measurement results can be used as the "previously acquired measurement results of the three-dimensional shape." In this case, the region setting unit can extract, as a candidate region, a region where the deviation from the past measurement results exceeds a standard.

[0027] In the sixth aspect, the region setting unit may predict changes in the three-dimensional shape over a predetermined period of time based on past measurement results, and extract, as a candidate region, a region where the predicted result after the predetermined period has elapsed exceeds a standard.

[0028] A measurement system according to a seventh aspect is any one of the first to sixth aspects, shape The measuring instrument measures the three-dimensional shape of the object based on the center frequency of a beat signal obtained by irradiating the object with frequency-modulated continuous wave laser light at a first pitch, and the vibration measuring instrument measures the vibration of the object based on FM sidebands obtained by irradiating the object with frequency-modulated continuous wave laser light at a second pitch coarser than the first pitch. If vibration measurement of a certain area takes longer than distance measurement (three-dimensional shape measurement) of an area of ​​the same size, the pitch of the vibration measurement can be made coarser than the pitch of the distance measurement, as in the seventh aspect.

[0029] The measurement system according to an eighth aspect is any one of the first to seventh aspects, wherein the laser scanners include a first laser scanner and a second laser scanner, both of which are supplied with frequency-modulated continuous wave laser light; the shape measuring instrument measures the three-dimensional shape of the object based on the center frequency of a beat signal obtained by the first laser scanner; and the vibration measuring instrument measures the vibration of the object based on the FM sideband obtained by the second laser scanner. As described above, the present invention uses a common laser light source, but as defined in the eighth aspect, the scanner for measuring the three-dimensional shape and the scanner for measuring the vibration may be separate. Such a configuration can be adopted depending on the required scanning speed and scanning range for the three-dimensional shape measurement and the vibration measurement.

[0030] The measurement system according to the ninth aspect is the measurement system of the eighth aspect, further comprising a splitter that splits the frequency-modulated continuous wave laser light and supplies it to the first laser scanner and the second laser scanner. As described above, the laser light source is common to the three-dimensional shape measurement and the vibration measurement, so when there are multiple scanners, the laser light is split and supplied.

[0031] The measurement system according to a tenth aspect is the measurement system according to any one of the first to ninth aspects, further comprising an evaluator that evaluates floating of the object based on the measured vibrations.

[0032] The measurement system according to an eleventh aspect is the same as any one of the first to tenth aspects, and further includes a display control unit that causes a display device to display the measured three-dimensional shape and the measured vibration in association with each other. According to the eleventh aspect, the user can easily visually grasp the measurement results. The display can be performed using, for example, letters, numbers, symbols, graphs, charts, images, etc., and these may be colored. For example, the measurement results of the three-dimensional shape and the measurement results of the vibration may be displayed superimposed on each other (conceivable examples include using vibration contour lines or pseudo-color representation). Furthermore, when float is evaluated, the display control unit may display the evaluation results of float in association with the three-dimensional shape and / or vibration.

[0033] A measurement system according to a twelfth aspect is any one of the first to eleventh aspects, in which the laser scanner scans a measurement object including a concrete structure, a metal member, or a plastic member. The "object" in the present invention is, for example, a social infrastructure structure such as a road, a bridge, a tunnel, a dam, or a building, e.g., a concrete structure, but is not limited thereto, and may also be a metal member or a plastic member, as defined in the twelfth aspect. It may also be a structure in which a concrete structure is combined with a metal member or a plastic member. [Effects of the Invention]

[0034] As described above, the measurement system of the present invention can measure the three-dimensional shape and vibration of an object with a simple configuration. [Brief explanation of the drawings]

[0035] [Figure 1] FIG. 1 is a diagram showing the principle of a pseudo-heterodyne LDV. [Figure 2] FIG. 2 is a diagram showing an example of a laser driving waveform and an example of a beat frequency of interference light. [Figure 3] FIG. 3 is a conceptual diagram illustrating the configuration of the measurement system according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing the center frequency and vibration frequency of the beat signal. [Figure 5] FIG. 5 is a diagram showing the state of signal processing in a frequency-shifted feedback laser. [Figure 6] FIG. 6 is a diagram showing the acquisition of three-dimensional point cloud data by scanning. [Figure 7] FIG. 7 is a diagram showing detection of vibration components by an FM receiver. [Figure 8] FIG. 8 is a diagram showing a beat signal when the object is not vibrating. [Figure 9] FIG. 9 is a conceptual diagram illustrating the configuration of a measurement system according to the second embodiment. [Figure 10]FIG. 10 is a diagram showing the relationship between shape measurement points and vibration measurement points. [Figure 11] FIG. 11 is a diagram showing how candidate regions for acoustic excitation are extracted and set based on the shape measurement results. [Figure 12] FIG. 12 is a diagram showing an example of vibration measurement results. [Figure 13] FIG. 13 is a conceptual diagram illustrating the configuration of a measurement system according to the third embodiment. [Figure 14] FIG. 14 is a conceptual diagram illustrating the configuration of a measurement system according to the fourth embodiment. [Figure 15] FIG. 15 is a conceptual diagram illustrating the configuration of a measurement system according to the fifth embodiment. [Figure 16] FIG. 16 is a diagram showing how a three-dimensional shape is measured using a laser. [Figure 17] FIG. 17 is a diagram showing the non-contact acoustic inspection. DETAILED DESCRIPTION OF THE INVENTION

[0036] [Principle of the pseudo-heterodyne laser Doppler vibrometer] This section explains the principles of the pseudo-heterodyne LDV (Laser Doppler Vibrometer). Note that the FMCW method is almost the same as the pseudo-heterodyne method, and the following principles also apply to vibration measurement using the FMCW method.

[0037] Figure 1 shows the principle of a pseudo-heterodyne LDV. Laser light output from laser light source 1 is split into reference light and object light by half mirror 2. The reference light is reflected by reference mirror 3, and the object light is reflected by measurement target 4 and enters photodetector 5 via half mirror 2, causing interference between the reference light and object light. Assume that the round-trip distance of the object light (optical path difference with the reference light) is ΔL, and the round-trip time (difference in time of flight with the reference light) is Δt.

[0038] Figure 2 shows an example of a laser drive waveform and an example of the numerical value of the beat frequency of the interference light. Part (a) of the figure shows an example of a laser drive waveform. In the example shown in this part, the transmitted wave TW is a triangular wave whose wavelength changes from λ1 to λ2 with a period T, and the received wave RW changes in a similar pattern, delayed by Δt (the round-trip time mentioned above) from the transmitted wave TW. At a certain time, the difference in wavelength between the transmitted wave TW and the received wave RW is Δλ.

[0039] Part (b) of Figure 2 shows an example of the numerical value of the beat frequency of the interference light. As shown in the formula in this part, for example, the wavelength fluctuation width (λ1-λ2) of the laser driving wave is set to 1 nm, and the frequency of the laser driving wave is set to f T (=1 / T) is set to 10 kHz, and the wavelength of the laser light before modulation is λ c is 850 nm (near infrared laser), the beat signal frequency of the laser driving wave is f BEAT is 83MHz.

[0040] The pseudo-heterodyne LDV is also described in, for example, Non-Patent Document 1 below.

[0041] [Non-Patent Document 1] “Pseudoheterodyne detection scheme for optical interferometers,” D. Jackson, A. Kersey et al., Electronics Letters pp. 1082-1083, Vol. 18, No. 25, 1982.

[0042] In the above-mentioned Non-Patent Document 1, the optical path difference is about several centimeters, and the beat frequency is 20 kHz. On the other hand, when non-contact measurement is performed on social infrastructure structures such as concrete structures, the distance is long, so the beat frequency is on the order of MHz as in the above example, which is much higher than the example in Non-Patent Document 1. Therefore, it is difficult to simply apply the method in Non-Patent Document 1 to measurement of social infrastructure structures.

[0043] [Distance and vibration measurement using frequency-shifted feedback lasers] Optical distance measurement using a frequency-shifted feedback (FSF) laser is described, for example, in the following Non-Patent Document 2. Non-Patent Document 2 describes a method of measuring distance by converting it into frequency using frequency-chirped light (OFDR: Optical Frequency Domain Reflectometry).

[0044] [Non-Patent Document 2] "Frequency-Shifted Feedback Lasers and Their Measurement Applications" by Koichiro Nakamura et al., [Retrieved January 24, 2023], Internet (https: / / www.jstage.jst.go.jp / article / lsj1973 / 27 / Supplement / 27_Supplement_114 / _pdf / -char / ja)

[0045] Furthermore, vibration measurement using an FSF laser rangefinder is described in, for example, Non-Patent Document 3 below.

[0046] [Non-Patent Document 3] "Vibration Measurement Using a Frequency-Shifted Feedback Laser," Takefumi Hara, Optical Technology Contact, August 2017 issue, Japan Opto-Mechatronics Association, [Retrieved January 24, 2023], Internet (http: / / www.joem.or.jp / 2017-8-4.pdf)

[0047] Non-Patent Document 3 focuses on the time response of the center frequency of the beat signal itself, and measures vibrations at low frequencies of up to several tens of Hz. For this reason, the technology of Non-Patent Document 3 is difficult to apply to measurements of social infrastructure structures such as concrete structures, where high-frequency vibrations (for example, the above-mentioned vibrations on the order of kHz) are expected. In contrast to such conventional technology, the present invention measures vibrations by detecting FM sidebands of the beat frequency (details will be described later).

[0048] [Example of measurement system according to the present invention] An embodiment of the measurement system according to the present invention will now be described in detail.

[0049] [Example 1] FIG. 3 is a conceptual diagram showing the configuration of a measurement system 10 (measurement system) according to a first embodiment. The measurement system 10 includes a laser device 100 (laser light source, interferometer). The laser device 100 includes a laser light source that outputs frequency-shifted feedback laser light (FSF laser light) and a control unit for the laser light source. The laser light source includes a laser medium, a mirror, an AOM (Acousto-Optic Modulator), etc. However, as described in Patent Document 1, an optical SSB modulator (SSB: Single Side Band) may be used as a frequency shifter. The FSF laser light output from the laser device 100 is split into reference light and measurement light by a half mirror 102 (interferometer), and the reference light is reflected by a reference mirror 104 (interferometer). Note that, although the following description will be given of a case in which the laser device 100 outputs frequency-shifted feedback laser light (FSF laser light), the laser light used in the present invention may be frequency-modulated continuous-wave laser light (FMCW laser light) other than FSF laser light. In addition to FSF laser light, frequency-modulated continuous-wave laser light can also be generated using a DFB (Distributed Feedback) semiconductor laser, a Fabry-Perot semiconductor laser, a surface-emitting semiconductor laser, etc. For example, if the drive current waveform of a semiconductor laser is controlled with a sawtooth or triangular waveform, the frequency changes according to the change in current, so it operates as a frequency-modulated continuous-wave laser.

[0050] The laser scanner 106 (laser scanner, interferometer) scans the object 500 (object, measurement object) with FSF laser light. That is, the laser scanner 106 irradiates the measurement area of ​​the object 500 with laser light while changing the scanning direction. The light reflected by the object 500 is mixed with the reference light by a half mirror or the like, thereby causing interference between the reference light and the reflected light.

[0051] The combined reference light and reflected light are split into two beams by a half mirror 108 (beam splitter). One beam is input to a shape measuring instrument 120 (shape measuring instrument) for three-dimensional shape measurement, and the other beam is input to a vibration measuring instrument 132 (vibration measuring instrument) for vibration measurement. A display control unit 140 (display control unit) can display the three-dimensional shape measurement results, vibration measurement results, etc. on a display device 142 (display device) (details will be described later).

[0052] In Example 1 and other examples described later, the functions of the signal processing unit, area setting unit, display control unit, FM demodulator, vibration measuring unit, evaluator, and other components of the measurement system can be realized using processors such as CPUs (Central Processing Units), FPGAs (Field Programmable Gate Arrays), and PLDs (Programmable Logic Devices) and / or various electrical circuits. When performing processing by these components, programs and data recorded on non-transitory, tangible recording media (not shown) such as ROMs (Read Only Memory) and flash ROMs can be used, and recording media (not shown) such as RAMs (Random Access Memory) can be used as working areas and temporary data recording areas during processing. The "non-transitory, tangible recording media" described above does not include non-tangible recording media such as carrier signals themselves and propagation signals themselves.

[0053] In addition to the above-mentioned elements, the measurement system 10 also includes an operation unit (keyboard, mouse, etc.) (not shown), through which the user can issue instructions regarding measurement and result display. The measurement system 10 also includes a recording device (a non-transitory, tangible recording medium such as a magneto-optical recording device or semiconductor memory, and its control unit) (not shown), and can record scan data and measurement data in this recording device. The measurement system 10 may perform measurements, evaluations, or predictions using data recorded in this recording device. These points are also applicable to other embodiments described below.

[0054] In Example 1, the object 500 may be a concrete structure such as a road, bridge, tunnel, or building, but the object measured in the present invention is not limited to a concrete structure and may include metal components, plastic components, or two or more of concrete, metal, and plastic (the same applies to the other examples described below).

[0055] [Measurement of distance and vibration based on beat signals] The principle of measurement based on the beat signal of the interfered light will be explained. Figure 4 is a conceptual diagram showing the beat signal. The center frequency of the beat signal corresponds to the distance to the measurement point (the part where the lift occurs, etc.), and the "center frequency" is The number When the center frequency is low, the distance to the measurement point is short, and when the center frequency is high, the distance is long. Specifically, according to Non-Patent Document 4, in distance measurement using frequency-chirped light (OFDR: Optical Frequency Domain Reflectometry), the beat frequency and the distance (strictly speaking, the optical path difference) are proportional to each other, as shown in Equation (1). Here, ν Bm is the m-th beat frequency, γ is the chirp rate, nL is the optical path difference of the interferometer, c0 is the speed of light in a vacuum, ν c is the frequency interval of the resonator, and the integer m is the difference in comb number between the interfering light waves at the beat order. Note that the second term in equation (1) is known by order discrimination.

[0056]

number

[0057] [Non-Patent Document 4] "Ultra-High Precision Optical Measurement Technology Using Frequency-Shifted Feedback Lasers," Takefumi Hara et al., Applied Physics (JSAP International), Vol. 74, No. 6, Pages 697-702, Published: June 10, 2005

[0058] In this way, by repeating distance measurements based on the center frequency, it is possible to measure a three-dimensional shape.

[0059] Meanwhile, whether or not FM sidebands occur in the beat signal depends on the presence of a lift. If there is no lift, no FM sidebands occur (see Figure 8 below), but if there is a lift, FM sidebands occur. Furthermore, the difference between the center frequency of the beat signal and the frequency of the FM sidebands corresponds to the vibration frequency of the lift. In this way, the vibration or lift of an object can be evaluated based on the presence or absence and degree of sidebands.

[0060] Although the measurement system according to Example 1 does not have a vibration sound source as in Examples 2 to 5 described later, even with this configuration it is possible to measure the natural vibration of the object 500. The "natural vibration" referred to here is vibration that occurs due to normal use or operation of the object, and specifically, for example, vibration of roads or bridges on which vehicles continuously pass, or of equipment that operates continuously.

[0061] [3D shape measurement principle] FIG. 5 is a diagram for explaining the principle of measuring a three-dimensional shape, and FIG. 6 is a diagram showing how three-dimensional point cloud data is acquired by scanning.

[0062] The laser scanner 106 scans in the direction (elevation angle Θ i ,Azimuth Φ i ), a spot i (i=1, 2, . . .) is formed on the object. The reflected light from this spot i is mixed (interfered) with the reference light, generating a beat signal. The shape measuring instrument 120 (shape measuring instrument) performs a fast Fourier transformation (FFT) on the beat signal to determine the scanning direction (elevation angle Θ i ,Azimuth Φ i ) distance L i The laser scanner 106 sequentially changes the scanning direction, which allows the shape measurement device 120 to calculate a data set of direction and distance (elevation angle Θ i ,Azimuth Φ i ,distance L i :i=1, 2,...) (see FIG. 6). distanceL i and the scan direction (elevation angle Θ i ,Azimuth Φ i ) is converted into a 3D point cloud (X i ,Y i ,Z i ), which allows the three-dimensional shape of the object 500 to be measured.

[0063]

number

[0064] [Extraction of vibration components by FM demodulation] FIG. 7 is a diagram for explaining the extraction of vibration components by FM demodulation. Part (a) of FIG. 7 shows the process of extracting vibration components (time waveform) from a beat signal. When the object is not vibrating, the beat signal has only a peak (center frequency), as shown in FIG. 8. However, when the object is vibrating, sidebands with the beat frequency as the carrier wave are generated on both sides of the center frequency (see FIG. 4). As a result, an FM signal (frequency-modulated signal) is obtained, as shown in part (b) of FIG. 7.

[0065] [FM Demodulation (Sideband Detection)] The FM demodulator 130 (FM receiver) demodulates the beat signal obtained by interference and detects the FM sideband. Demodulation can be performed using multiple stages, such as a quadrature demodulator, a PLL demodulator (Phase Locked Loop, PLL), or a digital demodulator. Part (c) of Figure 7 is a block diagram of a quadrature detector (quadrature demodulator), which is one type of FM demodulator. A quadrature detector independently determines the amplitude and phase of a signal based on the orthogonal relationship between the real and imaginary parts of an analytic signal (complex signal) generated from a real signal. Specifically, two orthogonal signals (sine wave and cosine wave) are mixed (multiplied) with the real signal in a mixer, and the amplitude and phase can be calculated from the in-phase component (I component) and quadrature component (Q component) that pass through an LPF (Low-Pass Filter). This allows the vibration component (amplitude and frequency of a sinusoidal waveform) to be extracted. Although quadrature detection can be performed using a Hilbert filter, an LPF is easier to implement than a Hilbert filter.

[0066] The vibration measuring device 132 may include circuits (adder circuits, LPFs, etc.) for extracting the amplitude and phase from the I and Q components.

[0067] [Relationship between vibration and floating] The evaluator 134 (evaluator) can evaluate the floating of the object based on the vibration components measured by the above-mentioned method (i.e., based on the presence or absence of FM sidebands and the magnitude of the FM sidebands). As described in Non-Patent Document 5 below, if it is assumed that a complete crack has occurred, the natural frequency f of the flexural vibration fr is expressed by the following equation (3).

[0068] [Non-Patent Document 5] "Research and Development of Non-Contact Acoustic Inspection Methods for Non-Destructive Inspection," Tsuneyoshi Sugimoto et al., Report on the Results of Research and Development of Technologies Contributing to the Improvement of the Quality of Road Policy, No. 22-3, New Road Technology Conference, July 2014, [Retrieved January 24, 2023], Internet (https: / / www.mlit.go.jp / road / / / tech / jigo / h22 / pdf / report22-3.pdf)

[0069]

number

[0070] Here, h is the depth of the defect from the concrete, a is the radius, E is Young's modulus, ν is Poisson's ratio, and ρ is density. From equation (3), it can be seen that the natural frequency is proportional to the depth of the defect and inversely proportional to the square of the radius (corresponding to the area).

[0071] When the object is a concrete structure, the actual vibration frequency is approximately several hundred Hz to 10 kHz due to the physical properties of concrete.

[0072] [Relationship between float progression and vibration frequency] In the early stages of lifting, the cracks are incomplete, so the vibration frequency that properly indicates the cracks cannot be obtained (the proportional relationship described above does not hold accurately), and the signal is expected to be weak.As the lifting progresses, the vibration frequency becomes clearly obtainable, and the vibration signal becomes more pronounced.

[0073] [Features of measurement in Example 1] [Relationship between processing speed of shape measurement and processing speed of vibration measurement] When measuring shape and vibration using the above-mentioned methods, it is thought that measuring vibration takes longer than measuring 3D shape. For this reason, if scanning is performed at the processing speed required for shape measurement (high-speed scanning is necessary to measure a wide range), there is a possibility that the processing of vibration measurement will not be able to keep up with the scanning speed. To address this issue, the following measures can be considered, for example.

[0074] (1) Solution 1: Perform a shape measurement scan and a vibration measurement scan The three-dimensional shape is measured using data obtained from the first scan to identify areas where there is a high possibility of lifting or the like occurring, and the area is then scanned again to measure vibration. In this case, FM demodulation does not need to be performed in the first scan. In this case, the measurement system 10 may be equipped with an area setting unit 122 (area setting unit: see Example 2 and FIG. 9 described later). (2) Solution 2: Measure vibration by thinning out the scan data The scan is performed once. All data is used to measure the 3D shape, and a portion of the data is thinned out to measure vibration (evaluate lifting). In this case, by making the pitch of the vibration measurement coarser than the pitch of the shape measurement, the two measurements can be performed simultaneously (in parallel) (see Example 2 and Figure 10, which will be described later). (3) Measure 3: Accumulate data and process it later The scan is performed once. All data is used to measure the 3D shape, and the scan data is stored. The stored data is used to measure vibrations in post-processing.

[0075] According to the first embodiment having the above configuration, the FSF laser light source (FMCW laser light source) is shared between three-dimensional shape measurement and vibration measurement, making it possible to measure the three-dimensional shape and vibration of an object with a simple configuration.

[0076] [Example 2] FIG. 9 is a diagram showing the configuration of a measurement system according to Example 2. The measurement system 11 according to Example 2 includes a vibration sound source 110 and can irradiate a target object 500 with sound to vibrate it. A device such as a Long-Range Acoustic Device (LRAD) can be used as the vibration sound source 110, which can apply a sound pressure of about 100 dB to the target object 500 from a point about 10 m away, for example. The measurement system 11 also includes an area setting unit 122 (area setting unit) that sets a sound irradiation area, and the vibration sound source 110 irradiates the set sound irradiation area with sound. Note that other configurations of the measurement system 11 are the same as those of the measurement system 10 according to Example 1, and therefore detailed description thereof will be omitted.

[0077] [Example 2: Measurement using a vibration source] In the second embodiment, in addition to three-dimensional shape measurement, non-contact acoustic inspection can be performed using the excitation sound source 110. The vibration measuring device 132 can measure the vibration of the object 500 excited by the sound emitted by the excitation sound source 110. Note that in the second embodiment, the same problem as in the first embodiment occurs regarding the scan speed, and therefore, the above-mentioned measures 1 to 3 can be taken to address this problem.

[0078] FIG. 10 is a diagram showing an example of the relationship between the pitch of shape measurement and the pitch of vibration measurement (grid points are shape measurement points, and circles are vibration measurement points). Part (a) of FIG. 10 shows an example (corresponding to the above measure 2) in which a scan is performed once and the pitch of vibration measurement (second pitch) is coarser than the pitch of shape measurement (first pitch), and vibration measurement is performed over a wide range of the object 500 (for example, the entire object 500). In this example, as shown in the unit area 600, the ratio of vibration measurement to shape measurement is 1:25.

[0079] On the other hand, part (b) of FIG. 10 shows an example of non-contact acoustic inspection based on the results of three-dimensional shape measurement (corresponding to the above-mentioned measure 1). In this example, the shape measuring device 120 measures the three-dimensional shape using data obtained by the first scan, and the region setting unit 122 extracts candidate regions to be acoustically irradiated based on the measured three-dimensional shape. The candidate regions are, for example, regions where damage such as lifting has occurred, or regions of the object 500 where the degree of damage is high or where damage is thought to be progressing. The pitch during acoustic inspection may be the same as the pitch used for shape measurement, as shown in unit region 610, or may be coarser than the pitch used for shape measurement, as shown in unit region 620.

[0080] [Extraction of candidate areas and setting of acoustic irradiation areas] The region setting unit 122 calculates the variation of the measured three-dimensional shape from the design information of the three-dimensional shape of the object 500 (object) and / or previously acquired measurement results of the three-dimensional shape, and can extract regions where the magnitude of the variation exceeds a standard as candidate regions. The "design information" can be, for example, three-dimensional data generated from CAD data, and the "previously acquired measurement results" can be past measurement results. The "standard" can be, for example, a threshold value for variation, and a threshold value set by the user can be used. The display control unit 140 can display the extracted candidate regions and the set acoustic irradiation regions on the display device 142 (display device).

[0081] FIG. 11 is a diagram showing the display of the candidate region and the acoustic irradiation region. Part (a) of FIG. 11 is a display example of the magnitude of the variation in the three-dimensional shape (the variation from the design information of the three-dimensional shape and / or the previously acquired measurement results of the three-dimensional shape). In the figure, the color intensity indicates the magnitude of the variation. The darker the color, the greater the variation, and the variation in regions 634 and 636 is greater than that in regions 630 and 632. In such a diagram, the region setting unit 122 and the display control unit 140 can overlay the magnitude of the variation based on the measurement with the image or design information of the object 500 to associate (correlate) the two. Note that the region setting unit 122 and the display control unit 140 may display the magnitude of the variation using saturation in addition to or instead of color intensity, or may display the color intensity in combination with letters, numbers, figures, symbols, graphs, etc.

[0082] The user can determine the acoustic irradiation area by referring to the displayed shape measurement results and instruct the setting of the acoustic irradiation area via an operation unit (not shown). In other words, the magnitude of the fluctuation can be easily grasped visually, and an appropriate acoustic irradiation area can be set. Part (b) of Figure 11 is an example of acoustic irradiation areas 635, 637 (dotted rectangular areas) specified by the user.

[0083] The region setting unit 122 sets a sound irradiation region based on a user's instruction, the vibration sound source 110 irradiates the sound irradiation region with sound, and the vibration measuring device 132 measures the excited vibration. The region setting unit 122 can set the sound irradiation region based on a user's instruction, but it may also set it automatically based on the shape measurement results. For example, the region setting unit 122 can set a region including an area where the magnitude of variation is equal to or greater than a threshold as the sound irradiation region.

[0084] [Example of vibration measurement results] The display control unit 140 can superimpose the measurement results from the vibration measuring instrument 132 on the image and design information of the object 500, and associate (make correspondence) the two. For example, the image and design information of the object 500 can be displayed on the display device 142 with characters, numbers, symbols, figures, colors, etc. according to the frequency and / or amplitude of the vibration. For example, as shown in FIG. 12, the display control unit 140 can display areas with high vibration frequencies or areas with large vibrations (areas 638 and 639 in the example of the figure) with darker colors.

[0085] Furthermore, the evaluator 134 can evaluate lifting or peeling based on the vibration measurement results, similar to Example 1. The evaluator 134 and the display control unit 140 may display the display results on the display device 142 or may record them in a recording device.

[0086] The display control unit 140 may display the shape and vibration measurement results and the evaluation results of lifting and peeling in chronological order on the display device 142 as charts, graphs, etc., or may display prediction results based on past measurement results. The shape measuring instrument 120 and the vibration measuring instrument 132 may predict shape changes, vibrations, and lifting (damage) by extrapolating past measurement results using linear or nonlinear functions, or may make predictions using a predictor built using machine learning or a prediction model built using other methods. Such predictions can be reflected in the evaluation of lifting and other damage, and in the planning of inspections, repairs, etc.

[0087] According to the second embodiment having the above configuration, similarly to the first embodiment, it is possible to measure the three-dimensional shape and vibration of an object with a simple configuration.

[0088] [Example 3] FIG. 13 is a diagram showing the configuration of a measurement system 12 (measurement system) according to a third embodiment. As in the first and second embodiments, the measurement system 12 shares a laser scanner 106 for measuring three-dimensional shapes and vibrations, while using separate interferometers for measuring three-dimensional shapes and vibrations. Specifically, a reference mirror 104 (interferometer) causes interference between a reference light and a reflected light, which is used to measure three-dimensional shapes, and a reference mirror 107 (interferometer) causes interference between a reference light and a reflected light, which is used to measure vibrations. A half mirror 109 splits the reflected light and supplies it to a three-dimensional measurement system and a vibration measurement system. Since the other configurations are the same as those in the first and second embodiments, detailed description thereof will be omitted.

[0089] In the third embodiment having the above-described configuration, three-dimensional shape measurement, vibration measurement, and floating evaluation can be performed in the same manner as in the first and second embodiments. That is, the three-dimensional shape and vibration of an object can be measured with a simple configuration. Furthermore, in the measurement system 12 according to the third embodiment, the light received by the laser scanner 106 passes through two half mirrors (half mirror 109 and half mirror 102) before being input to the shape measuring instrument 120, whereas the light input to the vibration measuring instrument 132 passes through the half mirror (half mirror 109) only once. This results in a high signal-to-noise ratio for vibration measurement. Note that the fast scanning speed for vibration measurement can be achieved as described above for the first and second embodiments.

[0090] [Example 4] FIG. 14 is a diagram showing the configuration of a measurement system 13 (measurement system) according to a fourth embodiment. The measurement system 13 includes a laser scanner 106A (first laser scanner) for shape measurement and a laser scanner 106B (second laser scanner) for vibration measurement, both of which are supplied with frequency-shifted feedback laser light. The laser light output from the laser device 100 is branched by a half mirror 101 (branch) and supplied to the laser scanner 106A and the laser scanner 106B. The laser scanner 106B used for vibration measurement can have a slower scanning speed (a scanning speed that matches the processing speed of the vibration measurement) than the laser scanner 106B used for three-dimensional shape measurement. The vibration measurement system of the measurement system 13 uses a reference mirror 107 (interferometer) and a half mirror 105 (interferometer) to cause interference between the reference light and the reflected light.

[0091] In the fourth embodiment having the above-described configuration, the three-dimensional shape and vibration of an object can be measured with a simple configuration, as in the first to third embodiments. The candidate areas and measurement results can be displayed in the same manner as described above with reference to Figures 11 and 12. Furthermore, the measurement system 13 according to the fourth embodiment has a feature that the signal-to-noise ratio of shape measurement and vibration measurement is high, since the light received by the laser scanner passes through the half mirror only once (half mirrors 105 and 102) before being input to the vibration measurement instrument 132 and the shape measurement instrument 120.

[0092] Furthermore, the measurement system 13 can perform appropriate scans according to the speed of each of the shape measurement and vibration measurement. Specifically, the measurement system 13 can extract and set candidate areas based on the 3D shape measurement results and perform acoustic exploration (shape measurement and vibration measurement can be performed separately), or it can perform 3D shape measurement and acoustic exploration in parallel. The scan pitch for these measurements can be set in the same way as described above with reference to FIG. 10.

[0093] [Example 5] FIG. 15 is a diagram showing the configuration of a measurement system 14 (measurement system) according to Example 5. As in Example 4, the measurement system 14 includes a laser scanner 106A (first laser scanner) for shape measurement and a laser scanner 106B (second laser scanner) for vibration measurement, both of which are supplied with frequency-shifted feedback laser light. Laser light output from a laser device 100 is split into two beams by a half mirror 102. One beam becomes reference light for shape measurement and is reflected by a reference mirror 104. The other beam is further split by a half mirror 103 (splitter). One beam is supplied to the laser scanner 106A, and the other beam is split by a half mirror 105, one of which becomes reference light and is reflected by a reference mirror 107, and the other is supplied to the laser scanner 106B.

[0094] Laser scanner 106A irradiates object 500 with laser light, and the reflected light is combined with a reference light for shape measurement, causing interference, and is input to a shape measurement system (shape measuring instrument 120, etc.) for use in shape measurement. Laser scanner 106B irradiates an acoustic irradiation area of ​​object 500 with laser light in conjunction with excitation by excitation sound source 110. The reflected light is combined with a reference light for shape measurement, causing interference, and is input to a vibration measurement system (FM demodulator 130, etc.) for use in vibration measurement and lift evaluation.

[0095] In the fifth embodiment having the above-described configuration, the three-dimensional shape and vibration of an object can be measured with a simple configuration, similar to the first to fourth embodiments. The candidate areas and measurement results can also be displayed in the same manner as described above with reference to FIGS.

[0096] Furthermore, in the measurement system 14, appropriate scans can be performed according to the speeds of the shape measurement and vibration measurement, as in the fourth embodiment, and the scan pitch for these measurements can be set in the same manner as described above with reference to Fig. 10. Furthermore, if a measurement system including a laser light source (laser device 100, half mirror 102, reference mirror 104) already exists, the measurement system 14 can be easily configured by adding equipment to this measurement system.

[0097] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described aspects and various modifications are possible. [Explanation of symbols]

[0098] 1. Laser light source 2 Half mirror 3 Reference Mirror 4 Measurement target 5 Receiver 10 Measurement System 11 Measurement System 12 Measurement System 13 Measurement System 14 Measurement System 100 Laser device 101 Half Mirror 102 Half Mirror 103 Half Mirror 104 Reference Mirror 105 Half Mirror 106 Laser Scanner 106A Laser Scanner 106B Laser Scanner 107 Reference Mirror 108 Half Mirror 109 Half Mirror 110 Excitation Source 120 Shape measuring instrument 122 Area setting section 130 FM Demodulator 132 Vibration measuring instrument 134 Evaluator 140 Display control unit 142 Display device 500 objects 600 unit area 610 unit area 620 unit area 630 areas 632 areas 634 areas 635 Sound irradiation area 636 areas 637 Sound irradiation area 638 areas 639 areas 700 Laser Scanner 710 Object 712 Reinforced concrete 714 Internal cracks 716 Corrosion 720 Laser Scanner Vibrometer 730 Excitation Source

Claims

1. a laser light source that outputs a frequency-modulated continuous wave laser beam; a laser scanner that scans an object with the frequency-modulated continuous wave laser light; an interferometer that splits the frequency-modulated continuous wave laser light into a reference light and a measurement light, and causes interference between the reference light and a light that is the measurement light reflected by the object; a shape measuring instrument for measuring a three-dimensional shape of the object based on a center frequency of a beat signal obtained by the interference; an FM demodulator that FM demodulates the beat signal obtained by the interference and detects an FM sideband; a vibration measuring device for measuring vibration of the object based on the FM sideband obtained by the detection; A measurement system comprising:

2. The measurement system according to claim 1 , wherein the laser light source outputs a frequency-shifted feedback laser beam as the frequency-modulated continuous wave laser beam.

3. Further provided is a vibration sound source that irradiates the object with sound to excite vibration, 3. The measurement system according to claim 1, wherein the vibration measuring device measures the vibration of the excited object.

4. Further, a region setting unit is provided to set a sound irradiation region into which the sound is irradiated, The measurement system according to claim 3 , wherein the excitation sound source irradiates the sound onto the set acoustic irradiation area.

5. The measurement system according to claim 4 , wherein the region setting unit extracts candidate regions that are candidates for the acoustic irradiation region based on the measured three-dimensional shape, and displays the extracted candidate regions on a display device.

6. The measurement system according to claim 5, wherein the region setting unit extracts as the candidate region a region in which variation from design information of the three-dimensional shape of the object and / or measurement results of the three-dimensional shape previously acquired exceeds a standard.

7. the shape measuring instrument measures a three-dimensional shape of the object based on the center frequency of the beat signal obtained by irradiating the object with the frequency-modulated continuous wave laser light at a first pitch; 3. The measurement system according to claim 1, wherein the vibration measuring instrument measures the vibration of the object based on the FM sidebands obtained by irradiating the object with the frequency-modulated continuous wave laser light at a second pitch coarser than the first pitch.

8. the laser scanner includes a first laser scanner and a second laser scanner both of which are supplied with the frequency-modulated continuous wave laser light; the shape measuring instrument measures the three-dimensional shape of the object based on the center frequency of the beat signal obtained by the first laser scanner; The measurement system according to claim 1 or 2, wherein the vibration measuring device measures the vibration of the object based on the FM sidebands obtained by the second laser scanner.

9. The measurement system according to claim 8 , further comprising a splitter that splits the frequency-modulated continuous wave laser light and supplies the split light to the first laser scanner and the second laser scanner.

10. The measurement system according to claim 1 or 2, further comprising an evaluator for evaluating floating of the object based on the measured vibrations.

11. The measurement system according to claim 1 , further comprising a display control unit that causes a display device to display the measured three-dimensional shape and the measured vibration in association with each other.

12. 3. The measurement system according to claim 1, wherein the laser scanner performs the scan on a measurement object including any one of a concrete structure, a metal member, and a plastic member.

Images