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

Measurement System

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

[0002] [Measurement of Social Infrastructure Structures] This section describes measurements of "social infrastructure structures" such as roads, bridges, buildings, tunnels, dams, and other buildings, particularly concrete structures. In recent years, the inspection and maintenance (understanding the condition of the structures and repairing them accordingly) of so-called "social infrastructure structures" such as roads, bridges, tunnels, dams, and buildings has become a major social issue. Inspection of 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 target object 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 reinforcing bars and steel frames, may also be used.

[0003] In such concrete structures, "floating" refers to a condition in which the concrete near the surface loses its integrity with the interior concrete due to continuous cracks within the concrete or construction defects that cause vibrations or deformation during use ("https: / / www.tukigata.co.jp / publics / index / 41 / "https: / / www.tukigata.co.jp / publics / index / 41 / ; according to the Tsukigata Co., Ltd. website). In this condition, cracks form within the concrete due to corrosion of the rebar, pushing up the surface of the concrete and creating a convex "floating" shape. Furthermore, as stated on the above website, concrete with floating can 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 "latency period, progression period, early acceleration period, late acceleration period, and deterioration period," but it is said that "internal deterioration that can be detected by tapping by humans begins midway 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 mm to 0.2 mm or more).

[0005] Conventionally, workers have checked the three-dimensional shape and vibration of an object by visual inspection or by tapping, but this type of work is time-consuming and laborious, and it can also be difficult to get close to the object.

[0006] In response to such a situation, 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 shape CV caused by deterioration of a reinforcing bar 712 (internal cracks 714 and corrosion 716) 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).

[0007] Japanese Patent Application Laid-Open No. 2021-096383

[0008] When measuring the three-dimensional shape of an object, if the influence of the shape due to 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 three-dimensional 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 of the 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 determined by measuring the vibration.

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

[0011] As described above, the 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.

[0013] [Basic Concept of the Present Invention] The present inventors have conducted extensive research into the combined use of the above-mentioned three-dimensional shape measurement and non-contact acoustic probing, and have noticed 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 a 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, i.e., 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). Each aspect of the present invention, which was created based on this idea, will be described below.

[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 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 causes interference between the reference light and light reflected from the object by the measurement light, 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, an FM demodulator that FM demodulates the signal obtained by the interference and detects FM sidebands, and a vibration measuring instrument that measures vibrations of the object based on the FM sidebands obtained by detection.

[0015] In the first mode, 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, thereby measuring the three-dimensional shape of the object. On the other hand, since the FM sideband corresponds to the vibration frequency of the object, the vibration of the object can be measured by FM demodulating the signal obtained by interference. Note that "FM" stands for frequency modulation.

[0016] As described above, the measurement system according to the first aspect can measure the three-dimensional shape and vibration of an object. In this case, since the laser light source that outputs FMCW laser light is used as the light source for three-dimensional shape measurement and the light source for vibration measurement, it is possible to prevent the system from becoming large-scale by simply combining 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 an object and normal vibrations caused by use (such as vibrations of roads or bridges on which vehicles constantly travel, or vibrations of equipment in continuous operation).

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

[0024] The measurement system according to a fourth aspect is the same as that of the third aspect, but further includes an area setting unit that sets a sound irradiation area into 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 a fifth aspect is the fourth aspect, 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. The fifth aspect defines one aspect of candidate region extraction and display.

[0026] In a measurement system according to a sixth aspect, the region setting unit extracts, as a candidate region, a region where the deviation from design information of the object's three-dimensional shape 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. The "design information" can be, for example, information based on CAD (Computer Aided Design) data of the object. 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, the "previously acquired measurement results of the three-dimensional shape" can be, for example, past measurement results. 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 of time exceeds a standard.

[0028] A seventh aspect of the measurement system is any one of the first to sixth aspects, in which 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] According to an eighth aspect, the measurement system of any one of the first to seventh aspects includes a first laser scanner and a second laser scanner, both of which are supplied with frequency-modulated continuous wave laser light, and 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 FM sidebands obtained by the second laser scanner. As described above, the present invention uses a common laser light source, but as specified 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 a ninth aspect is 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, and therefore, when multiple scanners are used, the laser light is split and supplied.

[0031] A 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 measurement system of any one of the first to tenth aspects, further including 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 may be, for example, letters, numbers, symbols, graphs, charts, images, etc., and may be colored. For example, the three-dimensional shape measurement results and the vibration measurement results may be displayed superimposed on each other (such as by using vibration contours or pseudo-color representation). Furthermore, when floatation is being evaluated, the display control unit may display the floatation evaluation results 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.

[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.

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

[0036] [Principle of Pseudo-Heterodyne Laser Doppler Vibrometer] The principle of the pseudo-heterodyne LDV (Laser Doppler Vibrometer) will be described. Note that the FMCW method is almost the same as the pseudo-heterodyne method, and the following principle also applies to vibration measurement using the FMCW method.

[0037] 1 is a diagram showing the principle of a pseudo-heterodyne LDV. Laser light output from a laser light source 1 is split into reference light and object light by a half mirror 2. The reference light is reflected by a reference mirror 3, and the object light is reflected by a measurement target 4 and enters a photodetector 5 via the half mirror 2, causing interference between the reference light and the 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] 2 shows an example of a laser drive waveform and an example of the beat frequency of the interference light. Part (a) of the figure shows an example of the laser drive waveform. In the example shown in part (a), the transmitted wave TW is a triangular wave whose wavelength varies from λ1 to λ2 with a period T, and the received wave RW varies in a similar pattern, delayed by Δt (the round-trip time mentioned above) from the transmitted wave TW. At a given time, the wavelength difference 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, when the wavelength fluctuation width (λ1-λ2) of the laser driving wave is 1 nm, and the frequency of the laser driving wave is f T (=1 / T) is set to 10 kHz, and the wavelength λ of the laser light before modulation is c is 850 nm (near infrared laser), the frequency f of the beat signal of the laser driving wave is BEAT becomes 83 MHz.

[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 measurement and vibration measurement using a frequency-shifted feedback laser] Optical distance measurement using a frequency-shifted feedback laser (FSF) 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 a 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] Further, vibration measurement using an FSF laser range finder 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. Therefore, 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 (e.g., 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 example of a measurement system according to the present invention will be specifically described.

[0049] First Embodiment FIG. 3 is a conceptual diagram illustrating 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 also be used as a frequency shifter. The FSF laser light output by 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). Although the following description will be given of the laser device 100 outputting 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 may also be generated using a distributed feedback (DFB) semiconductor laser, a Fabry-Perot semiconductor laser, a surface-emitting semiconductor laser, or the like. For example, if the drive current waveform of a semiconductor laser is controlled with a sawtooth wave or a triangular wave, the frequency changes in response to changes in current, and the laser 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 laser light onto the measurement area of ​​the object 500 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 below, the functions of the signal processing unit, area setting unit, display control unit, FM demodulator, vibration measuring unit, evaluator, etc. constituting the measurement system can be realized using processors such as a CPU (Central Processing Unit), FPGA (Field Programmable Gate Array), PLD (Programmable Logic Device), etc., and / or various electrical circuits. When processing by these units, programs and data recorded on non-transitory and tangible recording media (not shown) such as ROM (Read Only Memory) or flash ROM can be used, and recording media such as RAM (Random Access Memory) (not shown) can be used as a working area or temporary data recording area during processing. The above-mentioned "non-transitory and tangible recording media" does not include non-tangible recording media such as the carrier signal itself and the propagation signal itself.

[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 (not shown) (a non-transitory, tangible recording medium such as a magneto-optical recording device or semiconductor memory, and its control unit), and can record scan data and measurement data in this recording device. The measurement system 10 may perform measurements, evaluations, or predictions using the data recorded in this recording device. These points also apply to the other embodiments described below.

[0054] In Example 1, the object 500 may be, for example, 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 signal] The principle of measurement based on the beat signal of interfered light will be explained. Fig. 4 is a conceptual diagram showing a beat signal. The center frequency of the beat signal corresponds to the distance to the measurement point (such as the part where the lift occurs), and there is a relationship that "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), as shown in Equation (1), the beat frequency and the distance (strictly speaking, the optical path difference) are proportional to each other. 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 of equation (1) is known by order discrimination.

[0056]

[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 of the beat signal occur 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, an FM sideband occurs. 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 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 like Examples 2 to 5 described below, 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 over which vehicles continuously pass, or of equipment that operates continuously.

[0061] [Principle of Measuring Three-Dimensional Shape] 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 of the elevation angle Θ i , azimuth angle Φ i ), a spot i (i = 1, 2, ...) is formed on the object. A beat signal is generated by mixing (interfering with) the reflected light from this spot i with the reference light. 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 angle 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 angle Φ i , distance L i : i = 1, 2, ...) is obtained (see FIG. 6). i and the scan direction (elevation angle Θ i , azimuth angle Φi ) is converted into a three-dimensional point group (X i , Y i , Z i ), which allows the three-dimensional shape of the object 500 to be measured.

[0063]

[0064] [Extraction of vibration components by FM demodulation] Figure 7 is a diagram for explaining the extraction of vibration components by FM demodulation. Part (a) of Figure 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 Figure 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 Figure 4). As a result, an FM signal (frequency-modulated signal) is obtained, as shown in part (b) of Figure 7.

[0065] [FM Demodulation (Sideband Detection)] The FM demodulator 130 (FM receiver) FM demodulates the beat signal obtained by interference to detect the FM sideband. Demodulation can be performed using multiple stages, such as a quadrature demodulator, a PLL demodulator (Phase Locked Loop), or a digital demodulator. Part (c) of Figure 7 is a block diagram of a quadrature detector, 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 a 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 are passed through an LPF (Low-Pass Filter). This makes it possible to extract the vibration component (amplitude and frequency of a sinusoidal waveform). Although quadrature detection can also 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 Technology 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]

[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 the progression of lifting 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 it is assumed that the signal is weak. As the lifting progresses, it is thought that the vibration frequency becomes clear 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-described method, it is thought that measuring vibration takes longer than measuring three-dimensional shape. Therefore, 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, for example, the following measures can be considered.

[0074] (1) Countermeasure 1: Perform a shape measurement scan and a vibration measurement scan. Measure the three-dimensional shape using the data obtained from the first scan to identify areas where lifting or other problems are likely to occur, and then scan those areas 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 also include a region setting unit 122 (region setting unit: see Example 2 and FIG. 9, which will be described later). (2) Countermeasure 2: Thin out the scan data and measure vibration. A single scan is performed. Measure the three-dimensional shape using all the data, and measure vibration (evaluate lifting) using a portion of the thinned data. In this case, by setting 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 FIG. 10, which will be described later). (3) Countermeasure 3: Store the data and perform post-processing. A single scan is performed. Measure the three-dimensional shape using all the data, and store the scan data. Use the stored data to measure vibration in post-processing.

[0075] According to the first embodiment having the above configuration, by sharing the FSF laser light source (FMCW laser light source) for three-dimensional shape measurement and vibration measurement, it is 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 (vibration sound source) and can vibrate an object 500 by irradiating it with sound. A device such as an LRAD (Long-Range Acoustic Device) can be used as the vibration sound source 110, which can apply a sound pressure of approximately 100 dB to the object 500 from a point approximately 10 m away, for example. The measurement system 11 also includes a region setting unit 122 (region setting unit) that sets an acoustic irradiation region, and the vibration sound source 110 irradiates sound into the set acoustic irradiation region. Note that other configurations of the measurement system 11 are similar to those of the measurement system 10 according to Example 1, and therefore detailed description thereof will be omitted.

[0077] [Example 2: Measurement using excitation sound source] In Example 2, in addition to three-dimensional shape measurement, non-contact acoustic exploration 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 irradiated by the excitation sound source 110. Note that in Example 2 as well, the same problem as in Example 1 occurs with respect to the scan speed, and this can be addressed by the above-mentioned measures 1 to 3, etc.

[0078] 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-mentioned measure 2) in which a single scan is performed and the pitch of vibration measurement (second pitch) is coarser than the pitch of shape measurement (first pitch), thereby performing vibration measurement over a wide range of the object 500 (e.g., 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 Figure 10 shows an example of non-contact acoustic exploration 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 from the first scan, and the region setting unit 122 extracts candidate regions that are candidates for acoustic irradiation regions 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 the damage is thought to be progressing. The pitch during acoustic exploration 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 area 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 areas where the magnitude of the variation exceeds a standard as candidate areas. 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 variation threshold value, which may be set by the user. The display control unit 140 can display the extracted candidate areas and the set acoustic irradiation areas 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 of 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 a combination of color intensity 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] [Display Example of Vibration Measurement Results] The display control unit 140 can superimpose the measurement results from the vibration measuring device 132 on the image and design information of the object 500, and associate (correlate) the two. For example, the image and design information of the object 500 can be displayed on the display device 142 with letters, 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] 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 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] Figure 13 is a diagram showing the configuration of a measurement system 12 (measurement system) according to Example 3. As with Examples 1 and 2, 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. Other configurations are the same as those of Examples 1 and 2, so 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, the measurement system 12 according to the third embodiment has the advantage that the signal-to-noise ratio of vibration measurement is high because 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. Note that the fast scanning speed for vibration measurement can be achieved as described above for the first and second embodiments.

[0090] [Example 4] Figure 14 is a diagram showing the configuration of a measurement system 13 (measurement system) according to Example 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-shifted feedback laser light. Laser light output from a laser device 100 is split by a half mirror 101 (splitter) 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 (scanning speed matched to the processing speed of 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 reference light and 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 the advantage that the signal-to-noise ratio of shape measurement and vibration measurement is high because 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 speeds of the shape measurement and vibration measurement. Specifically, the measurement system 13 can extract and set candidate areas based on the results of the three-dimensional shape measurement and perform acoustic exploration (shape measurement and vibration measurement are performed separately), or it can perform three-dimensional 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. Similar to 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 serves as 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 serves as reference light and is reflected by a reference mirror 107, and the other is supplied to the laser scanner 106B.

[0094] The laser scanner 106A irradiates the 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 (such as the shape measuring instrument 120) for use in shape measurement. The laser scanner 106B irradiates the acoustic irradiation area of ​​the object 500 with laser light in combination with vibration generated by the vibration 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 (such as the FM demodulator 130) 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 in accordance with the speeds of the shape measurement and vibration measurement, as in Example 4, and the scan pitch during 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.

[0098] REFERENCE SIGNS LIST 1 Laser light source 2 Half mirror 3 Reference mirror 4 Measurement object 5 Light 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 Vibration sound source 120 Shape measuring device 122 Area 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 bar 714 Internal crack 716 Corrosion 720 Laser scanner type vibrometer 730 Excitation sound 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.

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