JP2015224891A - Detection method using sound wave, and non-contact acoustic detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detection method using a sound wave in which reduction of the detection reliability of a detection object (defective part or the like) due to an optical noise is suppressed.SOLUTION: In the detection method using a sound wave, the sound wave is radiated to a surface of an irradiated body including a detection object inside it, the vibration speed is measured at a plurality of measurement places on its surface, and the position of the detection object is determined. The detection method includes: a process of radiating the sound wave from a sound wave emission source, vibrating the surface of the irradiated body, and measuring the vibration speed at each measurement place; and a process of performing specific information processing on the basis of the obtained measurement result of the vibration speed.

Description

  The present invention relates to a detection method using a sound wave and a non-contact acoustic detection system.

  In recent years, deterioration of concrete structures has become a problem, and the inside diagnosis is required. Conventionally, various methods using ultrasonic waves have been proposed as diagnostic methods for the inside of concrete. In addition, for the purpose of detecting an article buried in the ground, a method of irradiating the ground surface with sound waves has been proposed.

  Patent Document 1 discloses a method of discriminating a non-defective product or a defective product by lightly hitting a concrete product with a hammer using an air cylinder and detecting a sound pressure level of a sound wave generated at this time with a noise meter. .

  In Patent Document 2, an ultrasonic wave is incident on a concrete structure by dropping a steel ball from a predetermined height onto the surface of the object to be inspected, and the propagating ultrasonic wave contacts the surface of the structure. There is disclosed a method for inspecting the presence or absence of cavities in a concrete structure by receiving the received accelerometer and analyzing the frequency spectrum of the received ultrasonic waves.

  However, in these methods, it is necessary to perform measurement in contact with the inspection object, and various problems arise.

  On the other hand, as a non-contact acoustic inspection method that does not need to approach an inspection object, a method according to Patent Document 3 and a method according to Non-Patent Document 1 by the present inventors are also known.

  These non-contact acoustic inspection methods are inspection methods in which a non-inspection object is vibrated from a distance with sound waves or ultrasonic waves, and vibration of the applied object is optically detected at a distance.

Japanese Patent Laid-Open No. 7-20097 JP 2000-2692 A JP-A-8-248006

Tsunemi Sugimoto, Noriyuki Utagawa, and 2 others, “Study on non-contact audio imaging for non-destructive inspection using SLDV and LRAD”, Proceedings of the 2012 Annual Conference of the Acoustical Society of Japan 1-5-7, March 2012

  The present inventor has eagerly pursued research and development, and has found that there is a possibility that the light reception level may be deteriorated depending on the state of the surface of the irradiated object, and there is a problem in the reliability of the vibration speed data obtained.

  The present invention provides a detection method using a sound wave and a non-contact acoustic detection system in which a decrease in reliability of detection of an object to be detected (defect portion or the like) due to optical noise due to reverberation, light reception leakage, or the like is suppressed. With the goal.

The inventor diligently studied and found a method for solving the above-mentioned problems, and completed the present invention.
The present invention includes the following (i) to (iii).
(I) Detection using a sound wave that irradiates a surface of an irradiation object including the detection target object, measures vibration velocity at a plurality of measurement points on the surface, and determines the position of the detection target object A method,
Irradiating a sound wave from a sound wave source, vibrating the surface of the irradiated object, and measuring a vibration speed at each measurement location;
After obtaining the amplitude spectrum (Sf) representing the relationship between the frequency and the vibration velocity at each measurement location based on the obtained vibration velocity, the relationship between the frequency and the vibration energy (PSD) is further obtained and obtained. Obtaining an integral value in a specific range for the relationship between the obtained frequency and vibration energy (PSD), and setting the measurement point where the integral value was the smallest value as the minimum PSD part;
Based on the following formula (I), a vibration energy ratio (VER (1)), which is a ratio of vibration energy of other measurement points to the minimum PSD part, is obtained, and the measurement point whose value is equal to or less than a threshold value is A step of determining that there is no object to be detected;
(PSDmin in the formula (I) means an integral value (integral range: f _{1 to} f ₂ ) regarding the relationship between the frequency and the vibration energy (PSD) in the minimum PSD section, and in the formula (I) PSDx means an integrated value (integral range: f _{1 to} f ₂ ) regarding the relationship between frequency and vibration energy (PSD) at a measurement location other than the minimum PSD portion.
Based on the following formula (II), spectrum entropy (H) is obtained from the amplitude spectrum (Sf), and in the previous step, the minimum PSD is measured at a measurement location other than the measurement location where the detection target is not present. A measurement location showing a lower spectral entropy (H) than the portion is determined as a location where the detection object exists, and conversely, a measurement location showing a spectral entropy (H) higher than the minimum PSD portion is a measurement failure location A process of judging
A detection method comprising:
(In the formula (II), Sf means an amplitude spectrum.)
(Ii) Further, n measurement points (n ≧ 2) on the surface of the irradiated object are respectively P ₁ , P ₂ ... P _x ..P _n (X is an integer of 1 to n). , arranged vibrational energy ratio in the measurement point P _x a (VER (1)), the measurement defective portion, except for the actual _{P 1, P 2 ··· P x} ·· position and similarity relationship P _n position The detection method as described in said (i) provided with the process of creating the distribution map of the vibration energy ratio shown.
(Iii) A non-contact acoustic detection system that irradiates a surface of an irradiated object including a detection target object with sound waves, measures vibration speeds at a plurality of measurement locations on the surface, and determines the position of the detection target object Because
An acoustic source that generates sound waves that can vibrate the surface of the irradiated object;
A measuring instrument for measuring the vibration velocity of the surface of the irradiated object;
Using the measurement result of the obtained vibration velocity, and having an analysis device that identifies the part where the detection target object exists and the part where it does not exist and the measurement failure part,
A non-contact acoustic detection system capable of performing the detection method according to (i) or (ii) above.

  ADVANTAGE OF THE INVENTION According to this invention, the detection method using a sound wave and the non-contact acoustic detection system which suppressed the fall of the reliability of the detection of the detection target object (defect part etc.) resulting from optical noise can be provided.

It is the schematic which shows the suitable aspect of the non-contact acoustic detection system of this invention. It is a flowchart which shows the typical example of specific information processing. It is a figure which shows the example of a vibration velocity waveform at the time of measuring with a laser Doppler vibrometer in the condition which does not apply acoustic excitation to a small concrete test piece. It is a figure which shows the Fourier-transform result of the vibration velocity waveform of FIG. It is the schematic of the apparatus used by the preliminary test. It is a figure which shows the relationship between the depth of a defect part, and vibration energy ratio. It is a figure which shows the measurement result of vibration energy ratio. It is the figure which illustrated the measurement result of vibration speed. It is a figure which shows the representative example of an amplitude spectrum (Sf). It is a figure which shows the measurement result of vibration energy ratio. It is a figure which shows the result of spectrum entropy (H). It is the figure which mapped the position of the healthy part, a defective part, and a measurement defect part. It is a distribution map of vibration energy ratio.

The present invention will be described.
The present invention is a detection method and a non-contact acoustic detection system. According to the detection method of the present invention and the non-contact acoustic detection system of the present invention, the position of the detection target inside the irradiated body can be accurately grasped. Examples of the irradiated body include concrete structures, the ground (such as earth, sand, stone, and asphalt), wood, liquid, and human body. Specifically, according to the detection method of the present invention and the non-contact acoustic detection system of the present invention, for example, the position of a land mine buried in the ground can be accurately grasped. In this case, landmines are detection objects. Moreover, the position of the defect part inside a concrete structure can be grasped | ascertained correctly. In this case, the defective part is a detection target. In addition, the position of a tumor or the like existing inside the human body can be accurately grasped. In this case, a tumor or the like is a detection target. In addition, it is possible to accurately grasp the positions of defective portions inside various products (that is, nondestructive inspection can be performed). In this case, the defective part is a detection target. Further, it is possible to accurately grasp the position of a detection object (an object having an acoustic impedance different from that of the surrounding liquid) located near the liquid surface such as a pond, sea, or lake.

  The detection method of the present invention is preferably realized by the non-contact acoustic detection system of the present invention. The non-contact acoustic detection system of the present invention irradiates the surface of the irradiated object including the detection target object with sound waves, measures the vibration velocity at a plurality of measurement points on the surface, and determines the position of the detection target object. A non-contact acoustic detection system for determining, an acoustic transmission source that generates a sound wave that can vibrate the surface of the irradiated object, a measuring instrument that measures a vibration speed of the surface of the irradiated object, and the obtained vibration Using the measurement result of the speed, it has an analysis device that identifies a site where the detection target object exists, a site where the detection target object does not exist, and the measurement failure location, and can perform specific information processing by the analysis device. A specific example of the non-contact acoustic detection system of the present invention is the apparatus shown in FIG.

  FIG. 1 shows an acoustic transmission source 11 that generates a sound wave that can vibrate the surface of the irradiated object 1, a measuring instrument 13 that measures the vibration speed of the surface of the irradiated object 1, and a detection target inside the irradiated object 1. It is the schematic which shows the apparatus 10 which has the computer 15 containing the analysis apparatus 151 used in order to pinpoint the position of the thing 3. FIG. The apparatus 10 shown in FIG. 1 further includes an arbitrary waveform generating device 17 and an amplifier 19, and the computer 15 further includes a control device 152 and a display unit 153. 17 can be controlled to generate a sound wave having a desired frequency from the sound source 11. Measurement can also be performed by synchronizing the control device 152 with the trigger signal generated by the arbitrary waveform generator 17. The display unit 153 can display a vibration velocity distribution diagram and the like described later. The display unit means a display screen or the like.

  In the non-contact acoustic detection system (apparatus 10) of the present invention shown in FIG. 1, the acoustic transmission source 11 is a flat speaker. In the non-contact acoustic detection system of the present invention, the number of acoustic transmission sources, the angle of the speaker, and the like are not particularly limited.

  As an acoustic transmission source, a parametric speaker can be preferably used in addition to a flat speaker, and specifically, LRAD (registered trademark) manufactured by American Technology can be preferably used. Moreover, although a loudspeaker can also be used, in this case, the distance between the acoustic transmission source and the irradiated object is relatively short. Other acoustic sources that can be used include a pulse laser, a high-pressure gas gun, and a shock tube.

In addition, the sound wave emitted from the acoustic transmission source to the irradiated object can be adjusted to a desired frequency (ω), and the surface of the irradiated object is measured so that the vibration speed can be measured by a measuring instrument. Any sound wave that can be vibrated in a direction other than a direction parallel to the surface (preferably, a direction perpendicular to the surface) is preferable, and sound waves (acoustic waves) in an audible band in which vibration amplitude is difficult to attenuate in air are preferable. Ultrasonic waves are difficult to use. This is because ultrasonic waves are greatly attenuated in vibration amplitude in air.
In addition, when the resonance frequency band of the irradiated object is unknown, the sound wave irradiated from the acoustic transmission source to the irradiated object is preferably white noise. This is because all frequencies are included.

  It is preferable to generate a sound pressure of 90 dB or more on the surface of the irradiated body by irradiating the irradiated body with sound waves from the acoustic transmission source, and it is more preferable to generate a sound pressure of about 100 dB.

In the non-contact acoustic detection system (apparatus 10) of the present invention shown in FIG. 1, the measuring device 13 is preferably a laser Doppler vibrometer, and the irradiated object 1 is irradiated with a laser 131, and the vibration speed of the surface is measured. Can be measured. The obtained vibration velocity data is used for analysis by the analysis device 151.
In the non-contact acoustic detection system of the present invention, the measuring instrument is not particularly limited as long as it can measure the vibration velocity of the surface of the irradiated object in a non-contact manner. For example, a laser displacement meter can be used, and a laser Doppler can be used. A vibrometer is preferred. This is because the vibration of the surface of the irradiated object can be accurately measured even if the irradiated object and the measuring instrument are relatively separated from each other.
Further, although it is possible to use a single laser type laser vibrometer capable of measuring vibration at one point at a time, it is preferable to use a scanning laser type laser vibrometer. Specific examples of the laser Doppler vibrometer that is a scanning vibrometer include PSV400-H4 manufactured by Polytech Japan. This laser Doppler vibrometer includes a part of an analysis device and a control device.

  In the non-contact acoustic detection system (apparatus 10) of the present invention shown in FIG. 1, the analysis apparatus 151 can perform specific information processing for specifying the position of the detection target 3 in the irradiated object 1. If there is no particular limitation. This specific information processing is provided in the detection method of the present invention and will be described in detail later.

In the non-contact acoustic detection system (apparatus 10) of the present invention shown in FIG. 1, the arbitrary waveform generator 17 is an apparatus that can generate a sound wave of a desired frequency from the acoustic transmission source 11 according to a command from the controller 152. . For example, a commercially available function generator that can generate noise waves and burst waves can be used. The waveform of the sound wave to be transmitted can usually be controlled by this arbitrary waveform generator. Normally, it is controlled manually for the sake of simplicity, but it is also possible to configure the system to control from the analysis device side. Measurement can also be performed by synchronizing the control device 152 with the trigger signal generated by the arbitrary waveform generator 17.
Moreover, the amplifier 19 is not specifically limited, For example, a commercially available audio amplifier etc. can be used.

  The non-contact acoustic detection system of the present invention has a configuration capable of implementing the detection method of the present invention.

Next, the detection method of the present invention will be described.
The detection method of the present invention irradiates the surface of the irradiated object including the detection target object with sound waves, measures the vibration velocity at a plurality of measurement points on the surface, and determines the position of the detection target object. This is a detection method using.
And the process of irradiating a sound wave from a sound wave transmission source, vibrating the surface of the said to-be-irradiated body, and measuring the vibration speed in each measurement location is provided.
This process uses, for example, the above-described non-contact acoustic detection system of the present invention, irradiates the object to be irradiated with white noise, and uses a measuring instrument such as a laser Doppler vibrometer to measure each position on the surface. This can be done by measuring the vibration speed at. The vibration speed can be obtained as a relationship with the measurement time (time).

  Note that it is preferable to perform gate processing on the measurement result here to extract only the target signal. The gate processing is processing for extracting a signal to be measured in terms of time and frequency, and examples thereof include processing described in Japanese Patent Application No. 2012-258888 already performed by the present inventor.

  The detection method of the present invention further includes each step of performing specific information processing described below.

  In the detection method of the present invention, as a process of performing specific information processing, an amplitude spectrum (Sf) representing the relationship between the frequency and the vibration speed at each measurement location is obtained based on the measurement result of the vibration speed obtained in the previous process. After the determination, the relationship between the frequency and vibration energy (PSD) was further determined, and the integral value was determined in a specific range for the relationship between the obtained frequency and vibration energy (PSD), and the integral value was the smallest value. A step of setting a measurement location as a minimum PSD portion;

In this step, the measurement result of the vibration velocity obtained in the previous step is Fourier-transformed to obtain an amplitude spectrum (Sf), and the relationship between the frequency and vibration energy (PSD) is obtained.
The vibration energy (PSD) is a value proportional to the square of the vibration speed.

  In addition, when a resonance frequency exists in a measuring instrument such as a laser Doppler vibrometer or when the influence of multiple reflection cannot be ignored, it is preferable to calculate energy within a specified range in the frequency domain once after Fourier transform.

Next, for the relationship between the obtained frequency and vibration energy (PSD), an integral value is obtained within a specific range.
Although the range to integrate is not specifically limited, It is preferable to integrate in the range which does not include the resonance frequency of a measuring device. For example, in the case where noise at a resonance frequency such as a laser Doppler vibrometer exists, a range not including the noise may be set as an integration range. Specifically, for example, when resonance frequency noise such as a laser Doppler vibrometer is present at 1 kHz or less, a range of 1350 Hz to 8000 Hz may be integrated.

In this way, the above integrated value is obtained for each measurement location. And the measurement location where the integral value was the smallest is taken as the minimum PSD part.
The measurement location determined to be the minimum PSD portion is considered as one of the locations where no detection target exists.

  Next, the detection method of the present invention obtains a vibration energy ratio (VER (1)), which is a ratio of vibration energy of other measurement points to the minimum PSD part, as a step of performing specific information processing. A step of determining a measurement location that is equal to or less than a threshold value as a site where the detection target object does not exist;

  The vibration energy ratio (VER (1)) is a ratio of vibration energy of other measurement points to the minimum PSD portion, and is calculated from the following equation (I).

That is, the denominator in the formula (I) (“PSD _min ” in the formula (I)) is an integral value (integration range: f _{1 to} f in the relationship between the frequency and the vibration energy (PSD) in the minimum PSD section. ₂ ). Then, the numerator in the formula (I) (“PSD _x ” in the formula (I)) is an integrated value (integral range: integration range) regarding the relationship between the frequency and vibration energy (PSD) at the measurement location other than the minimum PSD portion. f ₁ is a ~f _2).

Then, it is examined whether or not the obtained vibration energy ratio (VER (1)) is equal to or less than a threshold value.
The threshold value is generally determined by the material of the irradiated object. For example, it can obtain | require by the method described in the preliminary test mentioned later. For example, when the non-irradiated body is concrete, the threshold is about 3.6 to 4 dB.
A measurement location where the value of the vibration energy ratio (VER (1)) is equal to or less than the threshold value can be determined as a location where the detection target does not exist.

  Next, in the detection method of the present invention, as a step of performing specific information processing, spectrum entropy (H) is obtained from the amplitude spectrum (Sf), and in the previous step, the measurement is determined as a region where the detection target does not exist At a measurement location other than the measurement location, a measurement location showing a lower spectral entropy (H) than the minimum PSD portion is determined as a location where the detection target exists, and conversely, a spectral entropy (H) equal to or higher than the minimum PSD portion. Is determined as a measurement failure location.

  The spectral entropy (H) at each measurement location is calculated from the following formula (II).

  Here, Sf is an amplitude spectrum. Further, the frequency calculation range of the spectral entropy (H) is not particularly limited, but it is preferable to make the same as the above-described range for obtaining the integral value regarding the relationship between the frequency and the vibration energy (PSD).

  Next, in the previous step, at the measurement location other than the measurement location determined as the location where the detection target does not exist, the detection target is present at a measurement location that exhibits a lower spectral entropy (H) than the minimum PSD portion. It is determined that the part to be performed. Conversely, a measurement location that exhibits a spectral entropy (H) greater than or equal to the minimum PSD portion is determined as a measurement failure location.

A representative example of the series of processes as described above is shown as a flowchart in FIG. FIG. 2 is a flowchart for determining a defective portion and a healthy portion in a concrete structure. That is, the detection target object is a defective part.
As shown in FIG. 2, first, gate processing (time and frequency) is performed on each measurement point result, and only a target signal is extracted. Next, vibration energy is calculated (when a resonance frequency exists in the laser Doppler vibrometer, it is preferable to calculate the energy within the specified range in the frequency domain once after FFT (Fourier transform)). Next, the energy ratio is calculated by using the energy showing the lowest value in the measurement point as a reference for the healthy part. The calculated energy ratio is determined by a threshold value. Here, it is determined that there is no problem in the measurement data per se and the sound part is a healthy part. Since anything above the threshold may be a defective part or a measurement failure point, the spectral entropy is calculated next. Since the measurement defect point has high whiteness of the frequency spectrum, the calculated value of spectrum entropy should also show a high value. By using the threshold value based on the minimum value of the spectral entropy of the healthy part, it becomes possible to clearly determine the measurement failure point.

Detection method of the present invention, further, said measurement points n portions of the surface of the irradiated object (n ≧ 2), _{respectively, P 1, P 2 ··· P} x ·· P n (X is 1~n integer), and the vibration energy ratio of the measurement point P _x a (VER (1)), the measurement defective portion except for the actual P _1, P ₂ position and similarity relationship · · · P _x · · P _n It is preferable to include a step of creating a vibration energy ratio distribution chart arranged and shown at the position. Creating such a distribution map makes it easy to specify the position of the object to be detected.
A specific method will be described in an example described later.

  The background that the present inventor has reached the present invention including the determination using the spectral entropy (H) as described above will be described.

  As a result of diligent research and development by the inventor, the present inventors have found that there is a possibility that the light reception level is deteriorated depending on the surface condition of the irradiated object, and that there is a problem in the reliability of the obtained vibration speed data. In particular, it has been found that when the distance between the measuring instrument such as a laser Doppler vibrometer and the object to be irradiated becomes long (for example, about 5 m (about 10 m in a round trip)), the tendency tends to increase. For example, FIG. 3 shows an example of a vibration velocity waveform when measured with a laser Doppler vibrometer in a situation where acoustic excitation is not applied to a small concrete specimen at an actual distance of 5 m.

FIG. 3A is an example of a vibration velocity waveform at a point where light is leaked, and FIG. 3B is an example of a vibration velocity waveform at a point where measurement is possible.
Since acoustic excitation is not applied to a small concrete test piece, only the noise level (± 50 to 100 μm / s) of laser Doppler measurement should be detected. As shown in FIG. 4, there is a case where there is a singular point having a maximum value of 300 μm / s. The cause of this is thought to be the mixing of optical noise due to leakage of received light. If such data is used as it is, it can be considered that the defect determination is greatly affected.

FIG. 4 is a Fourier transform result (amplitude spectrum) of the vibration velocity waveform of FIG. FIG. 4A shows the Fourier transform results of FIG. 3A and FIG. 4B shows the Fourier transform results of FIG.
As shown in FIG. 4, the optical noise when light is leaked is detected as a large vibration amplitude due to external noise. On the other hand, the frequency characteristic of this signal is a characteristic close to white noise as shown in FIG. Therefore, a decision using spectral entropy was proposed. Spectral entropy (H) is a feature quantity representing the whiteness of the amplitude spectrum, and can be calculated by the above-described equation (II). The spectral entropy (H) has a high value for a white signal having a uniform spectrum. However, since this spectral entropy alone cannot determine the difference between the measurement failure point due to light leakage and the measured healthy part, a detection algorithm combined with evaluation by vibration energy ratio was proposed.

<Preliminary test>
In order to determine the threshold value of the vibration energy ratio when the object is a concrete structure, a preliminary test was performed.
This will be specifically described below.

  First, four types of concrete specimens 20 having a cylindrical shape and including a defective portion therein were prepared. There are four types of cylinder cross-section radii of 100 mm, 150 mm, 200 mm and 300 mm. The positions and sizes of the defect portions included in these are known in advance.

  Next, after placing the specimen 20 as shown in FIG. 5, a sound wave of 100 dB is generated on the surface of the specimen 20 by irradiating the specimen 20 with sound waves from the long-range acoustic radiation device (LRAD) 22. It was. Then, using a scanning vibrometer (SLDV) 24, the vibration velocity was measured at a plurality of locations on the surface.

  Next, the measurement result (relationship between vibration speed and time) of the vibration velocity at each measurement location was Fourier transformed to obtain an amplitude spectrum (Sf) for each measurement location. And the relationship between a frequency and vibration energy (PSD) was calculated | required based on the obtained amplitude spectrum (Sf). The vibration energy (PSD) is a value proportional to the square of the vibration speed.

Next, in the relationship between the obtained frequency and vibration energy (PSD), an integral value (hereinafter also referred to as “PSD integral value”) was obtained in a range from f ₁ = 1350 Hz to f ₂ = 8192 Hz. And vibration energy ratio (VER (3)) was calculated | required based on following Formula (III).
Here, PSD _defect is the vibration energy of the defective portion, and PSD _health is the vibration energy of the healthy portion.

Next, based on the result of the formula (III), the relationship between the depth of the defect and the vibration energy ratio (VER (3)) was obtained. The results are shown in FIG.
FIG. 6 shows that the depth of the defect and the vibration energy ratio (VER (3)) are almost inversely proportional. In particular, when the radius of the cross section of the specimen 20 is 200 to 300 mm, it can be seen that there is a strong correlation in a wide range of 40 to 100 mm.
This fact indicates that there is a possibility that the depth of the defect portion can be estimated by the vibration energy ratio (VER (3)).

Next, the vibration energy ratio (VER (4)) based on the following formula (IV) was obtained using PSD integrated values at eight locations in the healthy part of the specimen 20.
Here, the vibration energy ratio (VER (4)) was obtained by combining all the PSD integral values of the healthy part measured at eight locations. The results are shown in FIG.

  From FIG. 7, it was found that the vibration energy ratio (VER (4)) between the healthy parts varies in the range of +3.6 dB to -3.6 dB. From this, when the target object is a concrete structure, it was determined that 3.6 dB may be used as a threshold value for defect determination. Assuming that the threshold is 3.6 dB, it can be seen from FIG. 6 that a defect portion having a depth of about 80 mm can be detected at a radius of 200 mm.

<Actual test>
The surface of a steel plate girder bridge with a float in Nagoya City was irradiated with sound waves, and the vibration velocity was measured at 63 locations on the surface. Here, numbers 1 to 63 were assigned to the measurement points.
This will be specifically described below.

  A sound wave was applied to the surface of the steel plate girder bridge from a long-range acoustic emission device (LRAD) by a method similar to the method shown in FIG. 5, and a sound pressure of 100 dB was generated on the surface. Then, using a scanning vibrometer (SLDV), the vibration velocity was measured at each of 63 locations on the surface. A representative example of the measurement result of the vibration speed is shown in FIG. FIG. 8A, FIG. 8B, FIG. 8C, and FIG. 8D show the measurement results when the measurement location numbers are 32, 35, 43, and 53, respectively.

  Next, the measurement result (FIG. 8) of the vibration velocity at each measurement location (63 locations) was subjected to Fourier transform, and an amplitude spectrum (Sf) was obtained for each measurement location. And the amplitude spectrum (Sf) for the measurement location (63 pieces) was obtained. A typical example of such an amplitude spectrum (Sf) is shown in FIG. 9 (a), 9 (b), 9 (c), and 9 (d) show the amplitude spectra (Sf) of the measurement location numbers 32, 35, 43, and 53, respectively. It is.

  Next, based on the obtained amplitude spectrum (Sf), the relationship between the frequency and vibration energy (PSD) was determined. The vibration energy (PSD) is a value proportional to the square of the vibration speed.

Then, in the relationship between the obtained frequency and vibration energy (PSD), an integral value (PSD integral value) was obtained in a range from f ₁ = 1350 Hz to f ₂ = 8192 Hz.
As a result, the PSD integrated value of No. 32 became the smallest, so that No. 32 was recognized as the “minimum PSD part” and further judged to be a healthy part. And the vibration energy ratio (VER (1)) compared with No. 32 was calculated | required about the other measurement location (62 places). That is, the vibration energy ratio (VER (1)) at each of the 62 locations was determined with the denominator in the well formula (I) being No. 32 and the numerator at each other measurement location.
Then, as shown in FIG. 10, it was determined that the part where the vibration energy ratio (VER (1)) was equal to or less than the threshold (3.6 dB) was a healthy part. This threshold is a value obtained from the above-described preliminary test.

  Next, the spectral entropy was calculated based on the above-described formula (II) at each measurement location. The frequency calculation range of spectral entropy (H) was 1350-8192 Hz. The results are shown in FIG.

  As shown in FIG. 11, the spectral entropy (H) of No. 32, which is a healthy part, was 11.5. Therefore, those having a spectral entropy (H) of less than 11.5 (for example, Nos. 35 and 43) were determined as defective portions. Further, a spectrum entropy (H) of 11.5 or more (for example, No. 53) was determined as a measurement failure location.

  Through the series of determinations as described above, it was possible to determine the healthy part, the defective part, and the measurement defective part. When the positions of the healthy part, the defective part, and the defective measurement part in the relationship diagram between the vibration energy ratio and the spectral entropy (H) are mapped, the result is as shown in FIG.

  Further, based on the determination result, a distribution diagram of vibration energy ratio (VER (1)) was drawn. That is, a distribution diagram in which the vibration energy ratio (VER (1)) is arranged by expressing the height in shades so as to be the same as the actual positional relationship of each measurement point was drawn. The sound part is represented by a color close to black and the defective part is represented by a color close to white paper. As shown in FIG.

  FIG. 13A is a comparative example, and shows a distribution of vibration energy ratio (VER) when all measurement data is used. FIG. 13B shows the distribution of the vibration energy ratio (VER (1)) in a case where a portion determined to be a measurement failure point by vibration energy and spectral entropy is excluded. Here, for the sake of simplicity, interpolation was performed with the energy ratio set to 0 dB for a portion determined to be a measurement failure point. In addition, the white frame at the bottom in the figure is a portion marked with chalk as a floating portion by the hammering inspection. Compared to FIG. 13A, it can be seen that the response at the defective portion is clearer in FIG. 13B.

DESCRIPTION OF SYMBOLS 1 Irradiated object 3 Object to be detected 10 Apparatus 11 Sound transmission source 13 Measuring instrument 131 Laser 15 Computer 151 Analysis apparatus 152 Control apparatus 153 Display part 17 Arbitrary waveform generator 19 Amplifier 20 Specimen 22 Long-distance acoustic radiation apparatus 24 Scanning vibrometer

Claims (3)

This is a detection method using sound waves that irradiates the surface of an object to be detected including the detection target object, measures the vibration velocity at a plurality of measurement points on the surface, and determines the position of the detection target object. And
Irradiating a sound wave from a sound wave source, vibrating the surface of the irradiated object, and measuring a vibration speed at each measurement location;
After obtaining the amplitude spectrum (Sf) representing the relationship between the frequency and the vibration velocity at each measurement location based on the obtained vibration velocity, the relationship between the frequency and the vibration energy (PSD) is further obtained and obtained. Obtaining an integral value in a specific range for the relationship between the obtained frequency and vibration energy (PSD), and setting the measurement point where the integral value was the smallest value as the minimum PSD part;
Based on the following formula (I), a vibration energy ratio (VER (1)), which is a ratio of vibration energy of other measurement points to the minimum PSD part, is obtained, and the measurement point whose value is equal to or less than a threshold value is A step of determining that there is no object to be detected;
(PSDmin in the formula (I) means an integral value (integral range: f _{1 to} f ₂ ) regarding the relationship between the frequency and the vibration energy (PSD) in the minimum PSD section, and in the formula (I) PSDx means an integrated value (integral range: f _{1 to} f ₂ ) regarding the relationship between frequency and vibration energy (PSD) at a measurement location other than the minimum PSD portion.
Based on the following formula (II), spectrum entropy (H) is obtained from the amplitude spectrum (Sf), and in the previous step, the minimum PSD is measured at a measurement location other than the measurement location where the detection target is not present. A measurement location showing a lower spectral entropy (H) than the portion is determined as a location where the detection object exists, and conversely, a measurement location showing a spectral entropy (H) higher than the minimum PSD portion is a measurement failure location A process of judging
A detection method comprising:
(In the formula (II), Sf means an amplitude spectrum.) Further, n measurement points (n ≧ 2) on the surface of the irradiated object are P ₁ , P ₂ ... P _x ... P _n (X is an integer of 1 to n), and measurement points. vibration energy ratio of P _x a (VER (1)), except for the measurement defective portion, shown placed in a position of the actual _{P 1, P 2 ··· P x} ·· position and similarity relationship P _n The detection method according to claim 1, further comprising a step of creating a distribution map of vibration energy ratios. A non-contact acoustic detection system that irradiates a surface of an irradiated object including a detection target object with sound waves, measures vibration velocity at a plurality of measurement points on the surface, and determines the position of the detection target object. ,
An acoustic source that generates sound waves that can vibrate the surface of the irradiated object;
A measuring instrument for measuring the vibration velocity of the surface of the irradiated object;
Using the measurement result of the obtained vibration velocity, and having an analysis device that identifies the part where the detection target object exists and the part where it does not exist and the measurement failure part,
A non-contact acoustic detection system capable of performing the detection method according to claim 1.