JPH05188043A - Ultrasonic flaw detecting device - Google Patents

Abstract

PURPOSE:To eliminate the influence of interference by surface waves so as to perform the measurement of a defective position and thickness with high accuracy by removing surface wave receiving elements from the received waves, and separating only reflected waves from internal acoustic break points or the bottom part. CONSTITUTION:A surface wavelet memory circuit 21 memorizes the received waveform of surface waves acquired from such a sample as not to be interfered with reflected waves from the bottom part using a tire probe 5. A subtracting circuit 22 provided at a surface wavelet eliminating circuit 20 performs subtraction reading the surface wave prestored in the surface wavelet memory circuit 21 from the received signal waveform obtained from a receiving circuit 9 at the non-destructive inspection time of a civil work structure. Surface wave receive elements arriving propagating around the surface from the received waves of the civil work structure such as the asphalt paved road can be thereby removed, and only the reflected waves from the internal acoustic break points or the bottom part can be separated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detector for nondestructive inspection of the internal condition of an asphalt pavement or the like.

[0002]

2. Description of the Related Art Conventionally, ultrasonic flaw detectors used for non-destructive inspection of asphalt paved roads, etc., use ultrasonic transducers for transmission and ultrasonic waves for reception with water, glycerin, etc. interposed between them and the inspection object. The acoustic probes are arranged at a predetermined interval, and the ultrasonic reception waveform is observed with an oscilloscope to estimate the internal state of whether or not there is a defect such as a cavity.

However, the spot-like non-destructive inspection cannot sufficiently catch the internal defect, and the work for changing the measuring point is complicated, so that the inventors of the present application have used ultrasonic waves for transmission. We have proposed an ultrasonic flaw detector for non-destructive inspection of the internal condition of civil engineering structures such as asphalt paved roads using a tire probe with a built-in probe and ultrasonic transducer for reception (Japanese Patent Application). No. 3-242945).

According to the ultrasonic flaw detector using such a tire probe, by running the tire probe on the asphalt pavement to be inspected, the horizontal axis shows the traveling distance on the CRT screen. The tomographic images are continuously displayed, and internal defects such as cavities can be reliably found.

[0005]

However, in the ultrasonic flaw detector using the tire probe, the acoustic discontinuity inside the asphalt pavement or the reflected wave from the bottom of the asphalt pavement causes the vicinity of the surface. Since the propagating surface wave interferes, the rise of the reflected wave and the time when the reflected wave exists become unclear from the received waveform, and the accuracy of nondestructive inspection, for example, the identification of the defect position inside the asphalt paved road and the thickness measurement There was a problem that a large error was given to or the measurement became impossible.

For example, as shown in FIG. 7, when a nondestructive inspection is performed while rolling the tire probe 5 on the inspection surface 4 of the asphalt pavement 3, the transmission supercharger built in the tire probe 5 is used. The ultrasonic wave transmitted from the acoustic wave probe 1 passes through the underwater path which is the liquid medium in the tire, the propagation path of the longitudinal ultrasonic wave on the asphalt paved road, and the ultrasonic wave for reception via the path inside the tire. A longitudinal wave reflection echo including the information of the thickness H of the asphalt pavement is reached, reaching the probe 2.

At the same time, the ultrasonic waves transmitted from the transmitting ultrasonic probe 1 incorporated in the tire probe 5 are transmitted through the underwater route in the tire, the surface wave propagating route in the asphalt paved road, and the inside of the tire. A longitudinal wave reflection echo that reaches the receiving ultrasonic probe 2 through the underwater route and does not include the thickness information of the asphalt paved road, but includes the thickness information as a surface wave that becomes an interfering wave in thickness measurement etc. have a finger in the pie.

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to eliminate the influence of interference due to surface waves and to accurately measure defect positions and thicknesses. An object is to provide an ultrasonic flaw detector.

[0009]

To achieve this object, the present invention is constructed as follows. First, the present invention is directed to an ultrasonic flaw detector for nondestructive inspection of the internal condition of an asphalt pavement using a tire probe having a transmitting ultrasonic probe and a receiving ultrasonic probe. To do.

According to the present invention as such an ultrasonic flaw detector, the surface storing the received waveform of the surface wave obtained from the sample which is not interfered by the reflected wave from the bottom using the tire probe Wave wavelet memory circuit,
A subtraction circuit that removes the received wave of the surface wave read from the surface wave wavelet storage circuit from the received wave obtained during nondestructive inspection of the civil engineering structure is provided, and the surface of the received wave of the civil engineering structure such as an asphalt paved road is It is characterized in that the received component of the surface wave propagating in the vicinity is removed and only the reflected wave from the acoustic discontinuity point or the bottom is separated.

Further, a surface wave wavelet amplitude adjusting circuit for adjusting the amplitude of the surface wave read from the surface wave wavelet storage circuit so as to match the peak amplitude of the received surface wave, and the rising time of the received surface wave. A surface wave wavelet rise time adjustment circuit for adjusting the rise time of the surface wave read from the surface wave wavelet storage circuit is provided to ensure the surface wave wavelet even if the sound velocity changes due to the temperature change of the measurement object. So that it can be removed.

[0012]

According to the ultrasonic flaw detector of the present invention having such a configuration, the received waveform of the surface wave received at the time of inspection is
For example, it is stored in advance by using a sample of a sufficiently large asphalt concrete block that does not suffer from interference due to reflected waves from the bottom. At the time of actual inspection, by subtracting the surface wave reception waveform stored from the sample from the actual reception waveform, the reception component of the surface wave contained in the reception waveform is removed, and internal acoustic discontinuities (defects such as cavities) and The rise and duration of the longitudinal wave reflection echo from the bottom can be clarified, and the defect position and thickness measurement accuracy can be greatly improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an embodiment showing one embodiment of the present invention. In FIG. 1, 5 is a tire probe, in which a transmitting ultrasonic probe 1 and a receiving ultrasonic probe 2 are arranged in a downward direction inside a rubber tire 2 made of urethane rubber or the like. The tire 2 is filled with water as a liquid medium, for example.

When the inspection object 3 is an asphalt paved road or a civil engineering building structure such as a wall surface of a building, the attenuation and scattering of ultrasonic waves is large, and therefore, for example, 20 kHz to 100 kHz.
Low frequencies in the kHz range should be used.
For example, when the used center frequency fo is fo = 30 kHz, the speed of sound propagating through the inspection object 3 is about 3000 m.
/ S, the wavelength is about 10 cm.

Therefore, in the one-probe method in which transmission and reception are performed by one ultrasonic probe, at least 10 cm corresponding to the wavelength is used.
A certain amount of dead zone (uninspectable area) occurs. Therefore, in the present invention, in order to avoid the occurrence of this dead zone, the two probe method using the transmitting ultrasonic probe 1 and the receiving ultrasonic probe 2 is adopted. The detailed structure of the tire probe 5 is as shown in FIG. 2, for example.

In FIG. 2, a tire probe 5 is rotatably provided inside the apparatus body 40. The tire probe 5 has a rubber tire 23 made of hard urethane rubber and a gel sheet 24 mounted on the outside thereof. As the gel sheet 24, for example, a polymer gel-like elastic body disclosed in JP-A-1-304102 can be used.

Bearing portions 25 are provided on both sides of the rubber tire 23, and are rotatably mounted on a probe mounting shaft 27 fixed to the apparatus body 40 via bearings 26. An oil seal 28 is provided inside the bearing 26 to prevent the medium liquid such as water filled in the rubber tire 23 from leaking to the outside. A pedestal 30 is attached to the center of the probe attachment shaft 27, and a transmission ultrasonic probe 1 and a reception ultrasonic probe 2 are attached to the lower portion of the pedestal 30. Signal lines 31 and 32 are drawn from the transmitting and receiving ultrasonic probes 1 and 2, and are connected to the transmitting circuit 8 and the receiving circuit 9 shown in FIG.

Further, the device body 40 is provided with auxiliary wheels 33, which enables the device body 40 to stably run. Referring again to FIG. 1, a trigger circuit 7 and a transmission circuit 8 are provided as a transmission circuit unit for the transmission ultrasonic probe 1 provided in the tire probe 5. The trigger circuit 7 receives the timing control by the control circuit 6 and outputs a transmission trigger signal to the transmission circuit 8 at constant measurement intervals. When the transmission circuit 8 receives the trigger signal, the transmission circuit 8 produces a transmission pulse having a constant time width, and with this transmission pulse, the use center frequency fo =
A transmission signal obtained by amplitude-modulating 30 kHz is supplied to the transmission ultrasonic probe 1.

The receiving signal based on the ultrasonic echo from the receiving ultrasonic probe 2 provided on the tire probe 5 is received by the receiving circuit 9.
After being subjected to filtering such as signal amplification and noise removal, the signal is supplied to the signal processing circuit 10 via the surface wave wavelet removal circuit 20 newly provided in the present invention. Here, the reception signal to the reception circuit 9 is gated by the signal from the control circuit 6 which gives the transmission timing, and only the reception signal obtained during the gate effective period is output.

The signal processing circuit 10 performs predetermined signal processing on the received signal so that distance resolution can be obtained even at a position within a transmission wavelength of 10 cm. That is, the depth or thickness of the asphalt pavement, which is the inspection object 3, is 5 to 1
It is often about 0 cm, which is about the same as the wavelength used for ultrasonic waves. Therefore, a distance resolution equal to or less than the used wavelength is required.

The received signal processed by the signal processing circuit 10 to increase the distance resolution is given to the luminance signal modulation circuit 11, converted into a luminance signal according to the received level, and supplied to the CRT display device 16. The trigger signal from the trigger circuit 7 is supplied to the vertical sweep circuit 12 to set the vertical sweep cycle. The vertical sweep circuit 12 outputs to the CRT display device 16 a vertical sweep signal having a sweep speed determined by the speed of sound of ultrasonic waves propagating in the inspection object 3 (for example, about 3000 m / s).

Further, a tire rotation speed detector 13 for detecting the rotation speed of the rubber tire 23 as the tire probe 5 travels is provided. The detected rotation speed of the tire rotation speed detector 13 is given to the running distance calculation circuit 14, and since the diameter of the rubber tire 23 is fixed, the running speed is calculated using the tire rotation speed. The tire rotation speed detector 13 and the mileage calculation circuit 14 receive the initial reset signal supplied from the control circuit 6 at the start of the measurement, and the detected rotation speed = 0 and the mileage = 0.
It becomes the initial state of.

The traveling distance calculated by the traveling distance calculation circuit 14 is supplied to the horizontal sweep circuit 15. Horizontal sweep circuit 15
Outputs a horizontal sweep signal that designates the horizontal position of the CRT display device according to the traveling distance of the tire probe 5 as the display position. The CRT display device 16 has a brightness modulation by a vertical sweep line in accordance with vertical scanning by the vertical sweep signal from the vertical sweep circuit 12 at a position corresponding to the horizontal traveling distance determined by the horizontal sweep signal at each specific cycle by the control circuit 6. Image display for one line from the circuit 11 is performed.

An image storage device 18 is provided for the CRT display device 16, and image data swept in the past is sequentially stored in the image storage device 18, and past image data before the current traveling position, that is, the horizontal position is stored. The data is read from the image storage device 18 and displayed on the CRT display device 16, whereby continuous tomographic images due to the traveling of the tire probe 5 can be displayed.

Next, the surface wave wavelet removing circuit 20 newly provided in the present invention will be described in detail. First, the surface wave wavelet removing circuit 20 includes a surface wave wavelet storage circuit 21 and a subtraction circuit 22. In the surface wave wavelet storage circuit 21, the surface wave received waveform received by propagating on the surface of the inspection object 3 is stored in advance.

Specifically, as shown in FIG. 2, the ultrasonic probe for receiving the ultrasonic waves emitted from the transmitting ultrasonic probe 1 when the tire probe 5 is placed on the inspection object 3 The path to reach 2 is the surface wave of the path passing through
There are longitudinal echoes of the path through. So, for example,
When the inspection object 3 is an asphalt paved road, a sample of an asphalt concrete block simulating the asphalt paved road is prepared. This sample is an asphalt concrete block large enough to sufficiently separate or ignore the longitudinal wave reflection echo of the surface wave of the path shown in FIG. That is, the block may have a thickness H so that the reception of the longitudinal wave reflection echo from the bottom is started after the reception of the surface wave is completed.

The surface wave obtained by using the sample of the asphalt concrete block is as shown in FIG. 3 (b), for example. Not surprisingly, Figure 3
Surface wave wavelet storage circuit 2 of surface wave shown in (b)
As the storage process for 1, the surface wave reception waveform is sampled at constant intervals in synchronization with the transmission trigger from the trigger circuit 7, converted into digital data, and written and stored for a predetermined time based on the propagation time determined by the path. Should be done.

The subtraction circuit 22 provided in the surface wave wavelet removing circuit 20 reads out the surface wave stored in advance in the surface wave wavelet storage circuit 21 from the reception signal obtained from the reception circuit 9 and performs the subtraction. Thus, the surface wave waveform component included in the received signal is removed. Specifically, reading of the surface wave reception waveform stored in the surface wave wavelet storage circuit 21 is started in synchronization with the transmission trigger of the trigger circuit 7, and a raw reception signal is obtained from the reception circuit 9 in synchronization with the transmission trigger. Therefore, subtraction circuit 2 from this received waveform
A process of subtracting and removing the surface wave reception waveform read in 2 is performed.

Actually, a raw received waveform as shown in FIG. 3 (a) is obtained. In this raw received waveform, only the surface wave shown in FIG. 3B is included in the first half, but the reception of the bottom surface reflected longitudinal wave starts halfway to form an interference region of the surface wave and the bottom reflected wave, and the surface wave is formed in the middle. Since the reception of the wave is cut off, only the bottom reflection longitudinal wave is left. The surface wave is removed by subtracting the pre-stored surface wave reception waveform of FIG. 3B read from the surface wave wavelet storage circuit 21 from the raw reception waveform of FIG. 3A. It is possible to generate only the reception waveform after the surface wave removal processing shown in FIG. 3C, that is, the bottom surface reflection longitudinal wave.

Therefore, the surface wave wavelet removing circuit 2
The signal obtained from 0 becomes only the reception component of the longitudinal wave reflection echo from the acoustic discontinuity point or the bottom of the cavity inside the inspection object 3 and is not interfered by the surface wave, so that the CRT display device An accurate tomographic image can be displayed on 16. Moreover, the position of the internal defect or the thickness H of the inspection object 3 can be accurately measured by accurately measuring the propagation time of the bottom surface reflection longitudinal wave echo.

The surface wave wavelet storage circuit 21 stores a surface wave reception waveform using a sample block in advance according to the type of the inspection object 3 and switches the storage waveform depending on the type of the inspection object 3. Alternatively, the surface wave wavelet removal process may be performed. 4 is shown in FIG.
FIG. 9 is a configuration diagram of an embodiment showing another embodiment of the surface wave wavelet removing circuit 20 of FIG. 6, which is accurate even when the sound velocity in the object changes due to the temperature change of the object to be inspected during the surface wave wavelet removal. It is characterized by the function of adjusting the temporal position and amplitude of the surface wavelet so that the surface wavelet can be removed.

If this function is not provided, surface wave components may remain in the processed reception waveform. 4, the surface wave wavelet removing circuit 20 includes a surface wave wavelet storage circuit 21 and a subtraction circuit 22 of FIG.
In addition to the sound velocity measuring unit 42, the received wave storage circuit 43, the received wave rise time detection circuit 44, the received wave amplitude detection circuit 45,
A surface wave wavelet amplitude adjusting circuit 46 and a surface wave wavelet rising time adjusting circuit 47 are provided.

The processing of FIG. 4 will be described below.
First, the reception waveform obtained from the reception circuit 9 as shown in FIG. 3A is stored in the reception waveform storage circuit 43. Next, the rising time _tr of the surface wave portion and the peak amplitude _Vrp of the preset portion of the surface wave portion are detected from the received waveform data stored in the received waveform storage circuit 43 (see FIG. 3A).

Here, the surface wave portion for which the peak amplitude V _rp is to be detected is preset as follows. From the explanatory view of ultrasonic wave propagation in the inspection state of FIG. 5, in the tire probe 5, the propagation time difference Δt between the bottom surface reflection longitudinal wave propagation path and the surface wave propagation path is given by the following equation. Δt = 2 {(L / 2) ² + H ² } ^1/2 / V _L − (L−D) / V _S (1) where V _S : surface wave sound velocity (measured value) _{VL of the} asphalt paved road: Longitudinal wave velocity of asphalt pavement (measured value) L: Distance between ultrasonic transducers for transmission and reception (set value) H: Thickness of asphalt pavement (unknown amount, but rough value can be estimated) D : Diameter of transmitting / receiving ultrasonic probe (known) Incidentally, the sound velocity measuring unit 42 measures the surface wave sound velocity V _S and the longitudinal wave sound velocity V _{L in} the equation (1).

Therefore, if the frequency f is used,
Within n wavelengths that satisfy the following expression from the rising edge of the received wave, there is a region where only the surface wave does not interfere with the bottom surface reflected longitudinal wave. (N / f) <Δt = 2 {(L / 2) 2 + H 2} 1/2 / V L - (L-D) / V S (2) 6 asphalt pavement used in the experiment of the present invention 3 shows the dimensional relationship of the asphalt concrete block Sample 3 simulating.

Usually, at a temperature of about 70 [° C.], which is equivalent to the temperature of the laying work by the asphalt finisher, the surface wave sound velocity V _S = 1200 [m / s] and the longitudinal wave sound velocity V _L = 2300 [m / s]. Met.

Therefore, in the configuration shown in FIG. 6, a tire probe having a frequency f = 30 [kHz] and a distance L = 100 [mm] between the transmitting ultrasonic probe 2 and the receiving ultrasonic probe 1 is searched. When performing inspection work on the asphalt pavement 3 aiming at a thickness H of about 100 [mm] using the tentacles 5, it is clear that when these values are substituted into the equation (1), the received waveform In the inside, about 38 [μ
sec], the bottom reflection longitudinal wave arrives.

[0038] At this time, the wave number n is n <f [2 {(L / 2) 2 + H 2} 1/2 / V L - (L-
The range satisfying D) / V _S ] = 1.14 is a region where the bottom surface reflection longitudinal wave does not interfere with the surface wave.

That is, in the range where the surface wave rises up to about 1 wavelength or less, only pure surface wave which does not receive the interference of the bottom surface reflection longitudinal wave exists. Therefore, as shown in FIG. 3A, the peak amplitude V _rp of the portion within one wavelength from the rising edge of the reception waveform is detected by the reception wave amplitude detection circuit 45 in FIG. Moreover, the rise time t _r is the received wave rise time detecting circuit 44 of the surface wave portion from the received waveform data stored in the received waveform storage circuit 43
Detect with.

Subsequently, the surface wave wavelet storage circuit 21
Supposing that the peak amplitude within one wavelength from the rising edge of the surface wave data stored in the table is V _sp , each amplitude data of the surface wave data stored by using the surface wave wavelet amplitude adjusting circuit 46 is multiplied by V _rp / V _sp . .. With this, the amplitude of the surface wave data in the received waveform of the received wave storage circuit 43 which is actually measured,
The amplitude of the surface wave data obtained from the surface wave wavelet storage circuit 21 can be made uniform.

Next, the surface wave wavelet rising time adjusting circuit 47 stores the rising time t _rp of the surface wave portion in the received waveform data stored in the received wave memory circuit 43 and the surface wave wavelet memory circuit 21 at the same time. The rising times of the surface wave data are matched. By the above processing, a surface wave wavelet with the same amplitude can be prepared at the exact same position as the surface wave component in the received waveform obtained by actual measurement, so the surface wave propagation velocity and amplitude change due to temperature and other causes. However, the subtraction circuit 22 can appropriately remove the surface wave wavelet.

[0042]

As described above, according to the present invention, by removing the interference of the surface acoustic wave which becomes an interfering wave at the time of nondestructive inspection using the tire probe, the internal defect and the bottom surface are removed. It is possible to clarify the rising and existing time of the longitudinal reflected wave, and to significantly improve the accuracy of identifying the internal defect position and the thickness measurement.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a structural diagram of an embodiment of the tire probe shown in FIG.

FIG. 3 is an explanatory diagram showing a raw received waveform, a stored surface wave, and a received waveform after a surface wave removal process according to the present invention.

4 is a block diagram of an embodiment showing another embodiment of the surface wave wavelet removing circuit shown in FIG.

FIG. 5 is an explanatory diagram showing propagation states of surface waves and longitudinal waves.

FIG. 6 is an explanatory diagram showing a dimensional relationship of measurement sites for determining a waveform portion for detecting a peak amplitude of a surface wave.

FIG. 7 is an explanatory diagram showing interference of surface waves that occurs in a conventional tire probe.

[Explanation of symbols]

 1: Ultrasonic probe for transmission 2: Ultrasonic probe for reception 3: Inspection object (asphalt pavement) 4: Inspection surface 5: Tire probe 6: Control circuit 7: Trigger circuit 8: Transmission circuit 9: Reception circuit 10: Signal processing circuit 11: Brightness modulation circuit 12: Vertical sweep circuit 13: Tire rotation speed detector 14: Running distance calculation circuit 15: Horizontal sweep circuit 16: CRT display device 18: Image storage device 20: Surface Wave wavelet removing circuit 21: Surface wave wavelet memory circuit 22: Subtraction circuit 23: Rubber tire 24: Gel sheet 25: Bearing part 26: Bearing 27: Probe mounting shaft 28: Seal 30: Pedestal 31, 32: Signal line 33: Auxiliary wheel 40: Device body 42: Sound velocity measurement unit 43: Received wave storage circuit 44: Received wave rise time detection circuit 45: Received wave amplitude detection circuit 46: Surface wave Wavelet amplitude adjustment circuit 47: Surface wave wavelet rise time adjustment circuit

Claims (2)

[Claims] 1. An ultrasonic flaw detector for nondestructively inspecting an internal state of an object to be measured using a tire probe incorporating a transmitting ultrasonic probe and a receiving ultrasonic probe. A surface wave wavelet memory circuit that stores in advance the received waveform of the surface wave obtained from the sample that does not interfere with the reflected wave from the bottom using the probe, and the received wave obtained during the nondestructive inspection. And a subtraction circuit for removing the surface wave reception waveform read from the surface wave wavelet storage circuit, and removing the surface wave reception component propagating in the vicinity of the surface from the reception wave of the measurement target to remove the internal acoustic wave. An ultrasonic flaw detector characterized in that only reflected waves from a discontinuity or a bottom are separated. 2. The ultrasonic flaw detector according to claim 1, wherein:
Further, a surface wave wavelet amplitude adjusting circuit that adjusts the amplitude of the surface wave read from the surface wave wavelet storage circuit so as to match the peak amplitude of the received surface wave, and a rising time of the received surface wave. An ultrasonic flaw detector, further comprising: a surface wave wavelet rising time adjusting circuit for adjusting the rising time of the surface wave read from the surface wave wavelet storage circuit.