Assay system

Abstract

One embodiment of the present application provides a measurement system capable of measuring a three-dimensional shape and vibration of an object with a simple configuration. A measurement system according to one embodiment of the present application 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 light and a measurement light, inputs reflected lights of the reference light and the measurement light reflected on the object, and causes the reflected lights to interfere with each other, a shape measurer that measures a three-dimensional shape of the object based on a center frequency of a beat signal obtained through the interference, an FM demodulator that FM-demodulates a signal obtained through the interference to detect an FM sideband, and a vibration measurer that measures a vibration of the object based on the FM sideband obtained through the detection.

Description

Measurement system Technical Field

[0001] This invention relates to a technique for measuring objects using a laser beam. Background Technology

[0002] [Measurement of social infrastructure structures]

[0003] This document describes the measurement of "social infrastructure structures" (especially concrete structures), such as roads, bridges, tunnels, dams, and buildings. In recent years, the inspection and maintenance of these so-called "social infrastructure structures" (including understanding their condition and making corresponding repairs) has become a significant social issue. During the inspection of these social infrastructure structures, it is necessary to determine the presence and extent of damage (cracks or "lifting"), thus requiring the measurement of the object's three-dimensional shape and vibration. Furthermore, "Infra" is an abbreviation for "Infrastructure." And while "concrete structure" refers to a structure built using concrete, it can also use components other than concrete, such as steel reinforcement or steel frames.

[0004] In this type of concrete structure, concrete "buoyancy" refers to a state where continuous cracks occur within the concrete, or where construction defects cause vibration or deformation during use, resulting in a loss of integrity between the concrete near the surface and the internal concrete ("https: / / www.tukigata.co.jp / publics / index / 41 / "; based on the website of "Tsukigata Co., Ltd."). In this state, cracks form within the concrete due to corrosion of the reinforcing steel, causing the concrete surface to lift and create a convex "buoyancy." Furthermore, as described on the aforementioned website, in concrete that has developed buoyancy, if deterioration progresses or it is subjected to impact, it will peel off.

[0005] This process of bubbling or peeling is categorized into "latent period, progression period, early acceleration period, late acceleration period, and deterioration period," but it is described as "internal deterioration detectable by tapping sounds starting from the middle of the early acceleration period." The "early acceleration period" refers to a state where internal cracks (fissures) develop due to corrosion or expansion of the reinforcing steel, but deformation or cracks occur on the surface, with very small surface deformation (estimated to be a bulge of about 0.1mm to 0.2mm or more).

[0006] In the past, workers would visually inspect or tap on objects to determine their three-dimensional shape or vibrations. However, this method requires time and effort and is sometimes difficult to get close to the object being inspected.

[0007] To address this situation, a technique using a laser beam to measure the object in a non-contact manner can be considered. Figure 16 is a diagram showing the state of measuring the three-dimensional shape of an object 710 using a laser scanner 700. In the example shown in the figure, the convex shape CV caused by the deterioration of the steel reinforcement 712 (internal cracks 714, corrosion 716) is measured from a distance of 5 m. Furthermore, it is known to measure distances using a frequency-shifted feedback laser (FSF laser) (for example, see Patent Document 1). Patent Document 1 also describes a method for determining the three-dimensional shape by scanning the object with an FSF laser (repeatedly measuring the distance).

[0008] Previous technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2021-096383 Summary of the Invention

[0011] The technical problem to be solved by the invention

[0012] When measuring the three-dimensional shape of an object, if the influence of the shape originating from construction (the original shape may sometimes be raised or recessed) overlaps with the measurement results, false detections or missed detections may occur. Furthermore, even if damage occurs, minor damage may still be missed. Therefore, it is sometimes insufficient to fully inspect an object solely through three-dimensional shape measurement.

[0013] Therefore, it is possible to consider using three-dimensional shape measurement and non-contact acoustic probing (vibration measurement). This is because if the vibration of the damage can be measured, the damage can be detected and measured more accurately. Non-contact acoustic probing is based on the same principle as the sound of a worker tapping, for example, using a laser vibrometer to measure the vibration of an object caused by a vibrating sound source (acoustic vibration source). The concept of non-contact acoustic probing is illustrated in Figure 17. In the example in this figure, a laser scanner-type vibrometer 720 is used to measure the vibration of the object 710 generated by the vibrating sound source 730. Since the frequency or intensity of the vibration depends on the degree of damage, the degree of damage can be determined by measuring the vibration.

[0014] However, simply combining the above-mentioned three-dimensional laser measurement and non-contact acoustic detection results in a large system, leading to increased costs.

[0015] Thus, existing technologies cannot determine the three-dimensional shape and vibration of an object using simple structures.

[0016] The present invention was made in view of this situation, and its object is to provide a measurement system capable of measuring the three-dimensional shape and vibration of an object with a simple structure.

[0017] means for solving technical problems

[0018] [Basic Concept of the Invention]

[0019] The inventors of this application conducted in-depth research on the combined use of the aforementioned three-dimensional shape measurement and non-contact acoustic detection, and discovered that the FSF laser, as described in Patent Document 1, is a type of FMCW laser (FMCW: Frequency Modulated Continuous Wave laser) and a light source for an LDV (Laser Doppler Vibrometer) that can be used as a "pseudo-heterodyne method." The inventors derived the concept that "by also applying the FSF laser or FMCW laser to the vibration measurement of damage, i.e., by using a laser light source in both three-dimensional shape measurement and vibration measurement, the system can be simplified" (in addition, heterodyne LDV is not suitable for distance measurement or three-dimensional shape measurement). Hereinafter, various aspects of the present invention created based on this concept will be described.

[0020] [Various embodiments of the present invention]

[0021] To achieve the above objectives, the measurement system according to the first aspect of the present invention comprises: a laser source that outputs a frequency-modulated continuous-wave laser beam; a laser scanner that scans an object using 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 the reflected light from the reference beam and the measurement beam reflected on the object to interfere; a shape measuring device that measures the three-dimensional shape of the object based on the center frequency of a beat signal obtained through interference; an FM demodulator that performs FM demodulation on the beat signal obtained through interference to detect the FM sideband; and a vibration measuring device that measures the vibration of the object based on the FM sideband obtained through detection.

[0022] In the first method, the center frequency of the beat signal obtained through interference corresponds to the distance to the point where the laser beam was irradiated. Therefore, by scanning the object, the distances to multiple points can be obtained, thereby enabling the determination of the object's three-dimensional shape. On the other hand, the FM sideband corresponds to the vibration frequency of the object. Therefore, by performing FM demodulation on the signal obtained through interference, the vibration of the object can be determined. Furthermore, "FM" stands for Frequency Modulation.

[0023] As described above, the measurement system according to the first method is capable of measuring the three-dimensional shape and vibration of an object. In this case, by using a laser source that outputs an FMCW laser beam as both the light source for three-dimensional shape measurement and the light source for vibration measurement, the large size of the system caused by simply combining the two systems can be prevented.

[0024] Thus, the measurement system according to the first method can measure the three-dimensional shape and vibration of an object with a simple structure.

[0025] In addition, three-dimensional shape and vibration can be used to understand the state of an object (whether it is damaged, the degree of damage, etc.).

[0026] In Method 1 and the following methods, a "Frequency Modulated Continuous Wave Laser" (sometimes called a "FMCW laser") refers to a laser beam that transmits a frequency-modulated continuous wave, allowing the distance to be determined based on the frequency difference (beat frequency) between the transmitted and reflected waves. In measurements using a frequency-modulated continuous wave laser beam, the distance resolution is determined based on the frequency variation.

[0027] In addition, in Method 1 and the following methods, the three-dimensional shape measurement and vibration measurement can be performed simultaneously or in parallel, or they can be performed separately.

[0028] Furthermore, in the first method, the vibration source in the vibration measurement may or may not be present. Even without vibration based on a vibration source, it is possible to measure the natural vibration of the object or the normal vibration caused by use (vibration of roads or bridges where vehicles are constantly moving, vibration of continuously operating equipment, etc.).

[0029] The measurement system involved in Method 2 is the same as that in Method 1, where the laser source outputs a frequency-shift feedback laser beam as a frequency-modulated continuous-wave laser beam. Method 2 specifies the specific method of "frequency-modulated continuous-wave laser". A "frequency-shift feedback laser" (hereinafter sometimes called an FSF laser) is a laser with a structure that feeds back the output of a frequency shifter (such as the first diffraction light of an acousto-optic element) to a gain medium, and is a type of frequency-modulated continuous-wave laser.

[0030] The measuring system involved in the third method, in addition to the first or second method, includes a vibration source that irradiates a sound onto an object to excite vibration, and a vibration measuring device measures the excited vibration of the object. The third method specifies an example of a vibration source, for instance, a directional loudspeaker that can be used as the vibration source.

[0031] The measurement system of the fourth method, in addition to the third method, includes a zone setting unit. This zone setting unit sets the acoustic illumination zone of the irradiated sound, and the vibrating sound source irradiates sound into the set acoustic illumination zone. According to the fourth method, sound can be irradiated (vibrated) onto a desired area. The irradiated sound can be a portion of the object. Furthermore, the zone setting unit can set the acoustic illumination zone based on user instructions, or it can set it independently of user instructions.

[0032] The measurement system involved in Method 5, in Method 4, involves a region setting unit extracting candidate regions that can become acoustic illumination regions based on the measured three-dimensional shape, and displaying the extracted candidate regions on a display device. Method 5 specifies a method for extracting and displaying candidate regions.

[0033] The measurement system involved in the sixth method, in the fifth method, involves a region setting unit extracting regions where the deviation from the design information of the object's three-dimensional shape and / or the measurement results of the three-dimensional shape obtained in advance exceeds a reference, as candidate regions. The sixth method specifically specifies a method for extracting candidate regions. As "design information," for example, information based on the object's CAD data (Computer Aided Design) can be used. In this case, the region setting unit can extract regions where the deviation from the design value exceeds a reference, as candidate regions. Furthermore, as "measurement results of the three-dimensional shape obtained in advance," for example, past measurement results can be used. In this case, the region setting unit can extract regions where the deviation from the past measurement results exceeds a reference, as candidate regions.

[0034] In addition, in the sixth method, the region setting unit can predict the change of the three-dimensional shape within a specified period based on past measurement results, and extract the region whose prediction result exceeds the benchmark after the specified period as a candidate region.

[0035] The measurement system involved in Method 7, in any of Methods 1 to 6, involves a shape measuring device that measures the three-dimensional shape of an object based on the center frequency of a beat signal obtained by irradiating the object with a frequency-modulated continuous-wave laser beam at a first interval, and a vibration measuring device that measures the vibration of the object based on an FM sideband obtained by irradiating the object with a frequency-modulated continuous-wave laser beam at a second interval larger than the first interval. In cases where vibration measurement of a certain area takes longer than distance measurement (three-dimensional shape measurement) of a region of the same width, Method 7 allows for a wider interval for vibration measurement than for distance measurement.

[0036] The measurement system involved in the eighth embodiment, in any of the first to seventh embodiments, includes a first laser scanner and a second laser scanner that are both supplied with a frequency-modulated continuous wave laser beam. A shape measuring device measures the three-dimensional shape of the object based on the center frequency of the beat signal obtained from the first laser scanner, and a vibration measuring device measures the vibration of the object based on the FM sideband obtained from the second laser scanner. As described above, in this invention, the laser source is common, but as specified in the eighth embodiment, the scanner for three-dimensional shape measurement and the scanner for vibration measurement can be different. This structure can be adopted according to the requirements of the scanning speed or scanning range for three-dimensional shape measurement and vibration measurement.

[0037] The measurement system involved in the ninth method, in the eighth method, includes a splitter that branches the frequency-modulated continuous wave laser beam and supplies it to the first laser scanner and the second laser scanner. As described above, the laser source is common in both three-dimensional shape measurement and vibration measurement; therefore, in the case of multiple scanners, the laser beam is branched and supplied.

[0038] The measurement system involved in the 10th method, in any of the 1st to 9th methods, further includes an evaluator that evaluates the buoyancy of the object based on the measured vibration.

[0039] The measurement system according to the 11th embodiment, in any of the 1st to 10th embodiments, further includes a display control unit that displays the measured three-dimensional shape and the measured vibration in association on a display device. According to the 11th embodiment, the user can easily grasp the measurement results visually. The display can be made using characters, numbers, symbols, curves, graphs, images, etc., and colors can be added to them. For example, the measurement results of the three-dimensional shape and the vibration measurement results can be displayed simultaneously (contour lines or pseudo-color representations of vibration can be considered). Furthermore, in the case of evaluating buoyancy, the display control unit can display the evaluation results of buoyancy in association with the three-dimensional shape and / or vibration.

[0040] The measurement system involved in Method 12, in any of Methods 1 to 11, involves a laser scanner scanning a measurement object, including any one of concrete structures, metal components, and plastic components. The "object" in this invention is exemplified by social infrastructure structures such as roads, bridges, tunnels, dams, and buildings, such as concrete structures, but is not limited to this; as specified in Method 12, it can also be metal or plastic components. Furthermore, it can also be a structure composed of a combination of concrete structures and metal or plastic components.

[0041] Invention Effects

[0042] As explained above, the measurement system according to the present invention can measure the three-dimensional shape and vibration of an object with a simple structure. Attached Figure Description

[0043] Figure 1 is a diagram illustrating the principle of LDV in the pseudo-heterodyne mode.

[0044] Figure 2 is a diagram showing an example of a laser-driven waveform and an example of the beat frequency of the interference light.

[0045] Figure 3 is a conceptual diagram showing the structure of the measurement system involved in Example 1.

[0046] Figure 4 is a graph showing the center frequency and vibration frequency of the beat signal.

[0047] Figure 5 is a diagram showing the state of signal processing in a frequency-shift feedback laser.

[0048] Figure 6 is a diagram showing how 3D point cloud data is obtained through scanning.

[0049] Figure 7 shows the detection of vibration components using an FM receiver.

[0050] Figure 8 is a diagram showing the beat signal when the object is not vibrating.

[0051] Figure 9 is a conceptual diagram showing the structure of the measurement system involved in Example 2.

[0052] Figure 10 is a diagram showing the relationship between the shape measurement point and the vibration measurement point.

[0053] Figure 11 is a diagram showing the state of extracting and setting candidate regions for acoustic vibration based on shape measurement results.

[0054] Figure 12 is a diagram showing an example of vibration measurement results.

[0055] Figure 13 is a conceptual diagram showing the structure of the measurement system involved in Example 3.

[0056] Figure 14 is a conceptual diagram showing the structure of the measurement system involved in Example 4.

[0057] Figure 15 is a conceptual diagram showing the structure of the measurement system involved in Example 5.

[0058] Figure 16 is a diagram showing the state of a three-dimensional shape determined by a laser.

[0059] Figure 17 is a diagram showing the situation of non-contact acoustic detection. Detailed Implementation

[0060] [Principle of a laser Doppler vibrometer using pseudo-heterodyne method]

[0061] The principle of the pseudoheterodyne LDV (Laser Doppler Vibrometer) is explained. Furthermore, the FMCW method is almost identical to the pseudoheterodyne method, and the following principles also apply to vibration measurements using the FMCW method.

[0062] Figure 1 is a diagram illustrating the principle of LDV using a pseudo-heterodyne method. The laser beam output from laser source 1 branches into a reference beam and an object beam in a half-reflector 2. The reference beam is reflected on a reference mirror 3, and the object beam is reflected on the object being measured 4, and both beams are incident on the receiver 5 via the half-reflector 2, thus causing interference between the reference beam and the object beam. Assume the round-trip distance of the object beam (the difference in optical path between it and the reference beam) is ΔL, and the round-trip time (the difference in flight time between it and the reference beam) is Δt.

[0063] Figure 2 is a diagram showing an example of a laser-driven waveform and a numerical example of the beat frequency of the interference light. Part (a) of Figure 2 shows an example of a laser-driven waveform. In the example shown in this part, the transmitted wave TW is a triangular wave whose wavelength varies within the range of λ1 to λ2 within a period T, and the received wave RW changes with the same pattern after a delay of Δt (the aforementioned reciprocating time) from the transmitted wave TW. When focusing on a certain moment, the difference in wavelength between the transmitted wave TW and the received wave RW is Δλ.

[0064] Part (b) of Figure 2 shows a numerical example of the beat frequency of the interference light. As shown in the formula in this part, as an example, if the wavelength variation width (λ1-λ2) of the laser driving wave is set to 1 nm, and the frequency f of the laser driving wave is... T (=1 / T) is set to 10kHz, and the wavelength λ of the laser beam before modulation is set to... c If we set it to 850nm (near-infrared laser), then the frequency f of the laser driving wave's beat signal is... BEAT It becomes 83MHz.

[0065] Regarding LDV with pseudo-heterodyne method, it is also described, for example, in the following non-patent document 1.

[0066] [Non-Patent Literature 1] "Pseudoheterodyne detection scheme for optical interferometers", D. Jackson, A. Kersey et al., Electronics Letters pp. 1082-1083, vol. 18, No. 25, 1982.

[0067] In Non-Patent Document 1, the optical path difference is approximately several centimeters, and the beat frequency is 20 kHz. However, in the case of non-contact measurement of social infrastructure structures such as concrete structures, the long distance results in a beat frequency in the MHz range, as in the example above, which is significantly higher than in Non-Patent Document 1. Therefore, it is difficult to simply apply the method of Non-Patent Document 1 to the measurement of social infrastructure structures.

[0068] [Distance and Vibration Measurement Based on Frequency-Shift Feedback Laser]

[0069] Regarding optical distance measurement based on frequency-shifted feedback lasers (FSF), for example, it is described in Non-Patent Document 2 below. Non-Patent Document 2 describes a method for measuring distance by converting distance into frequency using frequency-chirped light (OFDR: Optical Frequency Domain Reflectometry).

[0070] [Non-Patent Document 2] "Frequency-Shift Feedback Laser and Measurement Applications" Koichiro Nakamura et al., [Searched January 24, 2023], Internet (https: / / www.jstage.jst.go.jp / article / lsj1973 / 27 / Supplement / 27_Supplement_114 / _pdf / -char / ja)

[0071] Furthermore, vibration measurement based on an FSF laser rangefinder is described, for example, in the following non-patent document 3.

[0072] [Non-Patent Document 3] "Vibration Measurement Based on Frequency Shift Feedback Laser", Takefumi Hara, Optical Technology Contact, August 2017, Japan Photonics & Optics Association, [Searched January 24, 2023], Internet (http: / / www.joem.or.jp / 2017-8-4.pdf)

[0073] Non-Patent Document 3 focuses on the time response of the center frequency of the beat signal itself, taking vibrations at low frequencies of around tens of Hz as the measurement object. Therefore, the technique of Non-Patent Document 3 is difficult to apply to the measurement of social infrastructure structures such as concrete structures that assume high-frequency vibrations (e.g., the aforementioned kHz-level vibrations). In response to this prior art, the present invention detects the FM sideband (FM sideband wave) of the beat frequency to measure vibration (details will be described later).

[0074] [Examples of the measuring system involved in this invention]

[0075] The embodiments of the measurement system involved in this invention will be described in detail.

[0076] [Example 1]

[0077] Figure 3 is a conceptual diagram showing the structure of the measurement system 10 (measurement system) according to Embodiment 1. The measurement system 10 includes a laser device 100 (laser source, interferometer). The laser device 100 has a laser source that outputs a frequency-shift feedback type laser beam (FSF laser beam) and a control unit for the laser source. The laser source includes a laser medium, a mirror, an AOM (Acousto-Optic Modulator), etc., but as described in Patent Document 1 above, an optical SSB modulator (SSB: Single Sideband) can also be used as a frequency shifter. The FSF laser beam output by the laser device 100 is split into a reference beam and a measurement beam by a half-reflector 102 (interferometer), and the reference beam is reflected on a reference mirror 104 (interferometer). In addition, the following description focuses on the case where the laser device 100 outputs a frequency-shift feedback type laser beam (FSF laser beam), but the laser beam used in this invention can also be a frequency-modulated continuous wave laser beam (FMCW laser beam) other than an FSF laser beam. Besides FSF laser beams, frequency-modulated continuous-wave laser beams can also be generated using DFB (Distributed Feedback) semiconductor lasers, Fabry-Perot semiconductor lasers, and surface-emitting semiconductor lasers. For example, if a sawtooth or triangular wave is used to control the drive current waveform of a semiconductor laser, the frequency changes according to the change in current, thus functioning as a frequency-modulated continuous-wave laser.

[0078] The laser scanner 106 (laser scanner, interferometer) scans the object 500 (object, measurement object) using an FSF laser beam. That is, while changing the scanning direction, the laser scanner 106 irradiates the measurement area of ​​the object 500 with a laser beam. The reflected light reflected from the object 500 is mixed with the reference light by a semi-reflective mirror, thereby producing interference between the reference light and the reflected light.

[0079] The synthesized reference light and reflected light are split into two beams in the semi-reflective mirror 108 (beam splitter). One beam is input to the shape measuring device 120 (shape measuring device) for three-dimensional shape measurement, and the other beam is input to the vibration measuring device 132 (vibration measuring device) for vibration measurement. The display control unit 140 (display control unit) can display the three-dimensional shape measurement results or vibration measurement results, etc., on the display device 142 (display device) (details will be described later).

[0080] Furthermore, in Embodiment 1 and other embodiments described below, the functions of the signal processing unit, area setting unit, display control unit, FM demodulator, vibration meter, evaluator, etc., constituting the measurement system can be implemented using processors such as CPUs (Central Processing Units), FPGAs (Field Programmable Gate Arrays), and PLDs (Programmable Logic Devices) and / or various circuits. During processing based on these units, programs or data recorded in non-transitory and tangible recording media (not shown) such as ROMs (Read Only Memory) or flash ROMs can be used as the working area or temporary data recording area during processing, and recording media such as RAMs (Random Access Memory) (not shown) can be used. However, the term "non-transitory and tangible recording media" does not include intangible recording media such as the carrier signal itself and the propagation signal itself.

[0081] In addition to the aforementioned components, the measurement system 10 also includes an operation unit (keyboard, mouse, etc., not shown), through which the user can issue instructions related to measurement or result display. Furthermore, the measurement system 10 includes a recording device (optical-magnetic recording device, semiconductor memory, or other non-transitory and tangible recording medium and its control unit, not shown), capable of recording scan data or measurement data. The measurement system 10 can use the data recorded in this recording device to perform measurement, evaluation, or prediction. These aspects are also the same in other embodiments described later.

[0082] In Example 1, the object 500 may be a concrete structure such as a road, bridge, tunnel, or building. However, the object measured in this invention is not limited to concrete structures and may also include metal parts, plastic parts, or two or more of concrete, metal, and plastic (the same applies in other embodiments described below).

[0083] [Distance and Vibration Measurement Based on Beat Signals]

[0084] The principle of measuring the beat signal based on the interference of light is explained. Figure 4 is a conceptual diagram showing the beat signal. The center frequency of the beat signal is equivalent to the distance to the measurement point (such as the part that produces the levitation), and there is a relationship that "the distance to the measurement point is closer when the center frequency is low, and farther when the center frequency is high". Specifically, according to Non-Patent Document 4, as shown in Equation (1), in distance measurement using frequency-chirped light (OFDR: Optical Frequency Domain Reflectometry), the beat frequency is proportional to the distance (strictly speaking, the optical path difference). Here, v Bm Let m be the beat frequency, Y be the modulation frequency, nL be the optical path difference of the interferometer, c0 be the speed of light in vacuum, and v be the frequency of the interferometer. c Let m be the frequency interval of the resonator, and m be the difference in COM numbers between the light waves that interfere with each other by the number of beats. In addition, the second term of equation (1) is known by the number of beats.

[0085] [Formula 1]

[0086]

[0087] [Non-Patent Document 4] "Ultra-high Precision Optical Measurement Technology Based on Frequency-Shift Feedback Laser", Yuan Wuwen et al., Applied Physics (JSAP International), Volume 74, No. 6, Pages 697-702, Publication Date: June 10, 2005

[0088] Thus, by repeatedly performing distance measurements based on the center frequency, the three-dimensional shape can be determined.

[0089] On the other hand, whether or not an FM sideband is generated depends on the presence of levitation. If there is no levitation, no FM sideband is generated (see Figure 8 below); if there is levitation, an FM sideband is generated. Furthermore, the difference between the center frequency of the beat signal and the frequency of the FM sideband corresponds to the vibration frequency of the levitation. Thus, the vibration or levitation of an object can be evaluated based on the presence and degree of the sideband.

[0090] Furthermore, the measurement system described in Example 1, like Examples 2 to 5 described later, does not have a vibration source, but it is still possible to measure the natural vibration of the object 500 in this configuration. "Natural vibration" as used here refers to vibration generated by the normal use or operation of the object, specifically, for example, the vibration of roads or bridges with continuous vehicle traffic, or continuously operating equipment.

[0091] [Principle of Three-Dimensional Shape Measurement]

[0092] Figure 5 is a diagram used to illustrate the principle of three-dimensional shape measurement, and Figure 6 is a diagram showing the state of acquiring three-dimensional point cloud data through scanning.

[0093] If the laser scanner 106 is along the scanning direction (elevation angle Θ) i Azimuth Φ i When a laser beam of modulated frequency is irradiated, a light spot i (i = 1, 2, ...) is formed on the object. A beat signal is generated by mixing the reflected light from this light spot i with the reference light (causing interference). The shape measuring device 120 (shape measuring device) performs a high-speed Fourier transform (FFT) on the beat signal, and can calculate the scanning direction (elevation angle Θ) based on the center frequency component of the beat signal. i Azimuth Φ i Distance L on ) i The laser scanner 106 sequentially changes the scanning direction, thereby the shape measuring device 120 obtains a dataset of direction and distance (elevation angle Θ) in each spot. i Azimuth Φ i Distance L i (i = 1, 2, ...) (Refer to Figure 6). Furthermore, the shape measuring device 120 is capable of measuring distance L. i and scanning direction (elevation angle Θ) i Azimuth Φ i The following equation (2) is used to convert the point cloud (X) into a three-dimensional point cloud. i Y i Z i This allows us to determine the three-dimensional shape of object 500.

[0094] [Formula 2]

[0095] X i =L i ×sinΘ i ×cosΦ i

[0096] Y i =L i ×sinΘ i ×sinΦ i

[0097] Z i =L i ×cosΘ i …(2)

[0098] [Extraction of vibrational components via FM demodulation]

[0099] Figure 7 illustrates the extraction of vibrational components via FM demodulation. Part (a) of Figure 7 shows the process of extracting the vibrational components (time waveform) from the beat signal. Regarding the beat signal when the object is not vibrating, as shown in Figure 8, the beat signal is only the peak value (center frequency). However, when the object vibrates, sidebands (sidebands) are generated on both sides of the center frequency, using the beat frequency as the carrier wave (refer to Figure 4). The result is the FM signal (the signal modulated at the frequency) shown in part (b) of Figure 7.

[0100] [FM demodulation (sideband detection)]

[0101] The FM demodulator 130 (FM receiver) demodulates the beat signal obtained through interference to detect the FM sideband. Demodulation can be performed in multiple stages, including quadrature demodulators, PLL demodulators (PLL: Phase Locked Loop), and digital demodulators. Part (c) of Figure 7 is a block diagram of a quadrature detector (quadrature demodulator) as one type of FM demodulator. The quadrature detector independently determines the amplitude and phase of the signal based on the orthogonality between the real and imaginary parts of the analytical signal (complex signal) generated from the actual signal. Specifically, two orthogonal signals (sine wave and cosine wave) can be mixed (multiplied) into an actual signal using a mixer, and the amplitude and phase are calculated based on the in-phase component (I component) and quadrature component (Q component) passed through the LPF (Low-Pass Filter). Therefore, it is possible to extract vibrational components (amplitude and frequency of a sinusoidal waveform). Alternatively, a Hilbert filter can be used for quadrature detection, but an LPF is easier to implement than a Hilbert filter.

[0102] Additionally, the vibration measuring device 132 may include circuitry (addition circuit, LPF, etc.) for extracting amplitude and phase from the I and Q components.

[0103] [The Relationship Between Vibration and Lifting]

[0104] The evaluator 134 (evaluator) can evaluate the levitation of the object based on the vibration components measured by the above method (i.e., based on the presence or absence and size of the FM sideband). Furthermore, as described in Non-Patent Document 5 below, assuming a complete crack has formed, the natural vibration coefficient f of the flexural vibration... fr It is represented by the following formula (3).

[0105] [Non-Patent Document 5] "Research and Development of Non-Contact Acoustic Probing Method for Non-Destructive Inspection", Sugimoto Tsunemi et al., Report on Research and Development Results of Technologies Contributing to Road Policy Quality 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)

[0106] [Formula 3]

[0107]

[0108] Here, h is the depth from the concrete to the defect, a is the radius, E is Young's modulus, v is Poisson's ratio, and p is density. As can be seen from equation (3), the natural vibration number is directly proportional to the depth of the defect and inversely proportional to the square of the radius (corresponding to the area).

[0109] In addition, when the object is a concrete structure, due to the physical properties of concrete, the actual vibration frequency is around 100Hz to 10kHz.

[0110] [Relationship between the progress of buoyancy and vibration frequency]

[0111] In the initial stage of buoyancy, since the crack is incomplete, it can be assumed that a suitable vibration frequency representing the crack cannot be obtained (the above proportional relationship cannot be held with high precision), and the signal is weak. It can be assumed that as buoyancy progresses, the vibration frequency can be clearly obtained, and the vibration signal is also significantly manifested.

[0112] [Characteristics based on measurements from Example 1]

[0113] [Relationship between processing speed for shape measurement and processing speed for vibration measurement]

[0114] It can be assumed that, when measuring shape and vibration using the methods described above, vibration measurement takes more time than three-dimensional shape measurement. Therefore, if scanning is performed at the processing speed required for shape measurement (high-speed scanning is needed to measure a wide range), the processing speed for vibration measurement may not keep up with the scanning speed. To address this, for example, the following solutions can be considered.

[0115] (1) Countermeasure 1: Perform shape measurement scanning and vibration measurement scanning.

[0116] The three-dimensional shape is determined using data obtained from the initial scan to identify areas with a high probability of buoyancy, etc., and the area is scanned again to measure vibration. In this case, FM demodulation may not be performed in the first scan. In addition, in this case, the measurement system 10 may include a region setting unit 122 (region setting unit: refer to Embodiment 2 and FIG9 described later).

[0117] (2) Countermeasure 2: Extract scanning data for vibration measurement

[0118] The scan is set to once. The three-dimensional shape is determined using all the data, and vibration (evaluation of buoyancy) is determined using a portion of the extracted data. In this case, by making the interval between vibration measurements coarser than the interval between shape measurements, the two measurements can be performed simultaneously (in parallel) (see Example 2 and Figure 10 described later).

[0119] (3) Countermeasure 3: Accumulate data and perform post-processing

[0120] The scan is set to once. The three-dimensional shape is determined using all data, and the scan data is pre-accumulated. Vibration is determined in post-processing using the accumulated data.

[0121] According to Embodiment 1 of the above structure, by sharing the FSF laser source (FMCW laser source) in both three-dimensional shape measurement and vibration measurement, it is possible to measure the three-dimensional shape and vibration of an object with a simple structure.

[0122] [Example 2]

[0123] Figure 9 is a diagram showing the structure of the measurement system according to Embodiment 2. The measurement system 11 according to Embodiment 2 includes a vibration sound source 110, which can irradiate sound onto the object 500 to amplify vibration. As the vibration sound source 110, a device such as an LRAD (Long-Range Acoustic Device) can be used, thereby applying a sound pressure of about 100 dB to the object 500 from a point about 10 m away, for example. Furthermore, the measurement system 11 includes a region setting unit 122 (region setting unit) for setting an acoustic irradiation area, and the vibration sound source 110 irradiates sound into the set acoustic irradiation area. In addition, the other structures in the measurement system 11 are the same as those in the measurement system 10 according to Embodiment 1, so detailed descriptions are omitted.

[0124] [Example 2: Measurement using a vibrating sound source]

[0125] In Example 2, in addition to three-dimensional shape measurement, non-contact acoustic detection using the vibration source 110 can also be performed. The vibration measuring device 132 can measure the vibration of the object 500 excited by the sound irradiated by the vibration source 110. In addition, in Example 2, the same problem as in Example 1 occurs regarding the scanning speed, which can be addressed by the countermeasures 1 to 3 described above.

[0126] Figure 10 is a diagram illustrating an example of the relationship between the spacing of shape measurements and the spacing of vibration measurements (grid points represent shape measurement points, and circular markers represent vibration measurement points). Part (a) of Figure 10 shows an example of performing vibration measurements over a wide area (e.g., the entirety of object 500) of object 500 by setting the scan to once, making the spacing of vibration measurements (second spacing) coarser than the spacing of shape measurements (first spacing) (corresponding to countermeasure 2 described above). In this example, as shown in unit area 600, the ratio of vibration measurement to shape measurement is 1:25.

[0127] On the other hand, part (b) of Figure 10 illustrates an example of non-contact acoustic probing based on the results of three-dimensional shape measurement (corresponding to countermeasure 1 described above). In this example, the shape measuring device 120 uses data obtained from an initial scan to measure the three-dimensional shape, and the area setting unit 122 extracts candidate areas that can become acoustic irradiation areas based on the measured three-dimensional shape. Candidate areas are, for example, areas where damage such as buoyancy has occurred, or a portion of the object 500 where the damage is considered to be high or progressing. As shown in unit area 610, the spacing during acoustic probing can be the same as the spacing of the shape measurement, or as shown in unit area 620, it can be coarser than the spacing of the shape measurement.

[0128] [Candidate region extraction and sound illumination region setting]

[0129] The region setting unit 122 can calculate the variation of the measured three-dimensional shape from the design information of the three-dimensional shape of the object 500 (object) and / or the measurement results of the three-dimensional shape obtained in advance, and extract the region whose variation exceeds the reference as a candidate region. The "design information" can be, for example, three-dimensional data generated from CAD data, and the "measurement results obtained in advance" can be past measurement results. Furthermore, the "reference" is, for example, a threshold for variation, and a threshold set by the user can also be used. Furthermore, the display control unit 140 can display the extracted candidate region or the set sound illumination region on the display device 142 (display device).

[0130] Figure 11 is a diagram showing the display status of the candidate area and the sound illumination area. Part (a) of Figure 11 shows an example of the display 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 measurement results of the three-dimensional shape obtained in advance). In the figure, color depth represents the magnitude of the variation. The darker the color, the greater the variation; the variation in areas 634 and 636 is greater than that in areas 630 and 632. In this diagram, the area setting unit 122 and the display control unit 140 can establish a correlation between the measured magnitude of the variation and the image or design information of the object 500 (establish a corresponding correlation). In addition to color depth, the area setting unit 122 and the display control unit 140 can also use chroma to display the magnitude of the variation, or alternatively, they can combine color depth with characters, numbers, graphics, symbols, curves, etc., for display.

[0131] The user can determine the acoustic illumination area by referring to the displayed shape measurement results and instruct the user to set the acoustic illumination area via an operation unit (not shown). That is, the user can easily grasp the magnitude of the change visually and instruct the user to set the appropriate acoustic illumination area. Part (b) of Figure 11 is an example of the acoustic illumination areas 635 and 637 (dashed rectangular portions) indicated by the user.

[0132] The zone setting unit 122 sets the acoustic illumination zone according to the user's instructions, the vibration source 110 irradiates sound into the acoustic illumination zone, and the vibration measuring device 132 measures the excited vibration. Alternatively, the zone setting unit 122 can set the acoustic illumination zone according to the user's instructions, but it can also set it automatically based on shape measurement results. For example, the zone setting unit 122 can set a region including areas where the size of the variation is greater than or equal to a threshold as the acoustic illumination zone.

[0133] [Example of vibration measurement results]

[0134] The display control unit 140 can establish a correlation (corresponding correlation) between the measurement results based on the vibration measuring device 132 and the image or design information of the object 500. For example, it can add characters, numbers, symbols, graphics, colors, etc. to the image or design information of the object 500 according to the frequency and / or amplitude of the vibration and display them on the display device 142. For example, as shown in FIG12, the display control unit 140 can mark areas with high vibration frequency or large vibration (areas 638 and 639 in this example) with dark colors.

[0135] Furthermore, the evaluator 134 can evaluate buoyancy or peeling based on the vibration measurement results, just like in Embodiment 1. The evaluator 134 and the display control unit 140 can display the results on the display device 142 or record the results on the recording device.

[0136] The display control unit 140 can display the measurement results of shape and vibration, as well as the evaluation results of buoyancy or peeling, in a time sequence on the display device 142 using graphs or curves, and can also display prediction results based on past measurement results. The shape measuring device 120 and the vibration measuring device 132 can extrapolate past measurement results using linear or nonlinear functions to predict shape changes, vibrations, and buoyancy (damage), or they can use predictors built through machine learning or prediction models built through other methods to make predictions. Such predictions can be reflected in the planning of evaluation, inspection, and repair of damage such as buoyancy.

[0137] According to Embodiment 2 of the above structure, similarly to Embodiment 1, the three-dimensional shape and vibration of an object can be measured with a simple structure.

[0138] [Example 3]

[0139] Figure 13 is a diagram showing the structure of the measurement system 12 (measurement system) according to Embodiment 3. Like Embodiments 1 and 2, Measurement System 12 uses the laser scanner 106 for both three-dimensional shape measurement and vibration measurement. However, the interferometers differ in the three-dimensional shape measurement and vibration measurement. Specifically, the reference light and reflected light based on the reference mirror 104 (interferometer) are interfered with for three-dimensional shape measurement, and the reference light and reflected light based on the reference mirror 107 (interferometer) are used for vibration measurement. The semi-reflective mirror 109 branches the reflected light and supplies it to both the three-dimensional measurement system and the vibration measurement system. Other structures are the same as in Embodiments 1 and 2, therefore detailed descriptions are omitted.

[0140] In Embodiment 3 of the above-described structure, three-dimensional shape measurement, vibration measurement, and levitation evaluation can be performed in the same manner as in Embodiments 1 and 2. That is, the three-dimensional shape and vibration of an object can be measured with a simple structure. Furthermore, in the measurement system 12 of Embodiment 3, the light received by the laser scanner 106 passes through two half-reflecting mirrors (half-reflecting mirror 109 and half-reflecting mirror 102) before being input to the shape measuring device 120, while the light input to the vibration measuring device 132 passes through only one half-reflecting mirror (half-reflecting mirror 109), thus exhibiting a high SN ratio for vibration measurement. In addition, regarding vibration measurement, the fast scanning speed can be addressed as described in Embodiments 1 and 2.

[0141] [Example 4]

[0142] Figure 14 is a diagram showing the structure of the measurement system 13 (measurement system) according to Embodiment 4. 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-shift feedback laser beams. The laser beam output from the laser device 100 is branched by a half-reflector 101 (brancher) and supplied to the laser scanners 106A and 106B. The scanning speed of the laser scanner 106B used for measuring vibration can be slower than that of the laser scanner 106B used for measuring three-dimensional shape (a scanning speed that matches the processing speed of vibration measurement). The vibration measurement system of the measurement system 13 uses a reference mirror 107 (interferometer) and a half-reflector 105 (interferometer) to cause interference between the reference light and the reflected light.

[0143] In Embodiment 4 of the above-described structure, similarly to Embodiments 1-3, the three-dimensional shape and vibration of the object can be measured with a simple structure. The display of candidate regions and measurement results can also be performed in the same manner as described in Figures 11 and 12. Furthermore, in the measurement system 13 of Embodiment 4, the light received by the laser scanner passes through only one half-reflector (half-reflector 105, 102) before being input to the vibration measuring device 132 and the shape measuring device 120, thus exhibiting a high SN ratio for both shape and vibration measurement.

[0144] Furthermore, the measurement system 13 can perform appropriate scans based on the speed of shape measurement and vibration measurement, respectively. Specifically, the measurement system 13 can also extract and set candidate regions based on the three-dimensional shape measurement results for acoustic probing (performing shape measurement and vibration measurement separately), or it can perform three-dimensional shape measurement and acoustic probing in parallel. The scanning intervals during these measurements can be set in the same way as described in Figure 10.

[0145] [Example 5]

[0146] Figure 15 is a diagram showing the structure of the measurement system 14 (measurement system) according to Embodiment 5. The measurement system 14, like that in Embodiment 4, includes a shape-measuring laser scanner 106A (first laser scanner) and a vibration-measuring laser scanner 106B (second laser scanner), both supplied with a frequency-shift feedback type laser beam. The laser beam output from the laser device 100 is branched into two beams in a half-reflector 102. One beam serves as a reference beam for shape measurement and is reflected on a reference mirror 104. The other beam is further branched by a half-reflector 103 (brancher). One beam is supplied to the laser scanner 106A, and the other beam is branched by a half-reflector 105, one of which serves as a reference beam and is reflected on a reference mirror 107, while the other is supplied to the laser scanner 106B.

[0147] Laser scanner 106A irradiates the object 500 with a laser beam. The reflected light is combined with a reference beam for shape measurement and interferes with it. This interference is then input into a shape measurement system (shape measuring device 120, etc.) for shape measurement. Laser scanner 106B, together with a vibration source 110, irradiates the object 500 with a laser beam into the acoustic illumination area. The reflected light is combined with the reference beam for shape measurement and interferes with it. This interference is then input into a vibration measurement system (FM demodulator 130, etc.) for vibration measurement or buoyancy evaluation.

[0148] In Embodiment 5 of the above structure, similarly to Embodiments 1-4, the three-dimensional shape and vibration of the object can be measured with a simple structure. The display of candidate regions and measurement results can also be performed in the same manner as shown in Figures 11 and 12.

[0149] Furthermore, in the measurement system 14, appropriate scanning can be performed according to the speed of shape measurement and vibration measurement, just as in Embodiment 4, and the scanning interval during these measurements can be set in the same way as described in FIG10. Moreover, if a measurement system including a laser light source (laser device 100, semi-reflective mirror 102, reference mirror 104) already exists, the measurement system 14 can be easily constructed by adding equipment to that measurement system.

[0150] The embodiments of the present invention have been described above, but the present invention is not limited to the above-described manner and can be modified in various ways.

[0151] Symbol Explanation

[0152] 1-Laser source, 2-Semi-reflective mirror, 3-Reference mirror, 4-Object to be measured, 5-Photodetector, 10-Measuring system, 11-Measuring system, 12-Measuring system, 13-Measuring system, 14-Measuring system, 100-Laser device, 101-Semi-reflective mirror, 102-Semi-reflective mirror, 103-Semi-reflective mirror, 104-Reference mirror, 105-Semi-reflective mirror, 106-Laser scanner, 106A-Laser scanner, 106B-Laser scanner, 107-Reference mirror, 108-Semi-reflective mirror, 109-Semi-reflective mirror, 110-Vibration sound source, 120-Shape measuring device, 122-Area Domain setting unit, 130-FM demodulator, 132-vibration measuring device, 134-evaluator, 140-display control unit, 142-display device, 500-object, 600-unit area, 610-unit area, 620-unit area, 630-area, 632-area, 634-area, 635-sound irradiation area, 636-area, 637-sound irradiation area, 638-area, 639-area, 700-laser scanner, 710-object, 712-reinforcing steel, 714-internal crack, 716-corrosion, 720-laser scanner type vibration meter, 730-vibration sound source.

Claims

1. A measurement system comprising: a laser source that outputs a frequency-modulated continuous-wave laser beam; a laser scanner that scans an object by 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 the reflected light from the measurement beam on the object; a shape measuring device that measures the three-dimensional shape of the object based on the center frequency of a beat signal obtained through the interference; an FM demodulator that demodulates the signal obtained through the interference to detect the FM sideband; and a vibration measuring device that measures the vibration of the object based on the FM sideband obtained through the detection.

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

3. The measuring system according to claim 1 or 2, further comprising: a vibration sound source, irradiating the object with sound to excite vibration, and the vibration measuring device measuring the excited vibration of the object.

4. The measuring system according to claim 3, further comprising: a region setting unit, for setting an acoustic irradiation region to which the sound is irradiated, wherein the vibrating sound source irradiates the sound into the set acoustic irradiation region.

5. The measuring system according to claim 4, wherein, The region setting unit extracts candidate regions that can become the sound illumination region based on the measured three-dimensional shape, and displays the extracted candidate regions on the display device.

6. The measuring system according to claim 5, wherein, The region setting unit extracts regions from which the variation of the design information of the three-dimensional shape of the object and / or the measurement results of the three-dimensional shape obtained in advance exceeds the reference as candidate regions.

7. The measuring system according to claim 1 or 2, wherein, The shape measuring device determines the 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 beam at a first spacing, and the vibration measuring device determines the vibration of the object based on the FM sideband obtained by irradiating the object with the frequency-modulated continuous wave laser beam at a second spacing larger than the first spacing.

8. The measuring system according to claim 1 or 2, wherein, The laser scanner includes a first laser scanner and a second laser scanner that are jointly supplied with the frequency-modulated continuous wave laser beam. The shape measuring device measures the three-dimensional shape of the object based on the center frequency of the beat signal obtained from the first laser scanner. The vibration measuring device measures the vibration of the object based on the FM sideband obtained from the second laser scanner.

9. The measurement system according to claim 8, comprising: a brancher for branching the frequency-modulated continuous wave laser beam and supplying it to the first laser scanner and the second laser scanner.

10. The measuring system according to claim 1 or 2, further comprising: an evaluator for evaluating the buoyancy of the object based on the measured vibration.

11. The measurement system according to claim 1 or 2, further comprising: a display control unit that displays the measured three-dimensional shape in association with the measured vibration on a display device.

12. The measuring system according to claim 1 or 2, wherein, The laser scanner scans an object that includes any one of concrete structures, metal parts, or plastic parts.

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