Noncontact deformation detecting device with inclination measurement

This application is based upon and claims the benefit of priority from Japanese Patent Application No. P2016-010212, filed Jan. 22, 2016, the entire contents of which are incorporated herein by reference.

Embodiments described herein relate generally to a technology for detecting deformation (crack, crackle, or internal defect) of a structure such as a bridge or a tunnel.

Conventionally, a device for detecting deformation such as a crackle of a structure such as a bridge, a tunnel and the like in a non-contact manner is known (for example, see Japanese Unexamined Patent Application Publication No. Hei 8-248006). The device disclosed in Japanese Unexamined Patent Application Publication No. Hei 8-248006 irradiates a measurement point of an object with an ultrasonic wave and irradiates the measurement point with laser light, and measures a vibration state of the measurement point such as a resonance frequency, amplitude characteristics and attenuation characteristics. The device detects the deformation on the basis of the vibration state of the measurement point.

FIG. 1 is a schematic front view of a deformation detecting device;

FIG. 2 is a diagram illustrating a modification of arrangement of transducers;

FIG. 3 is a schematic diagram illustrating a parametric speaker and laser Doppler vibrometers;

FIG. 4 is a block diagram illustrating principles of distance measurement and vibration measurement of the laser Doppler vibrometer;

FIG. 5 is a diagram schematically illustrating output of a photodiode;

FIG. 6 is a timing chart illustrating operation principles of a gate section and a counter;

FIG. 7 is a flowchart illustrating the flow of a deformation detecting processing of a CPU;

FIG. 8 is a diagram illustrating a transmission path of an ultrasonic wave in a case in which a crack is generated in a measuring plane;

FIG. 9 is a diagram illustrating distances to measurement points in a case in which the measuring plane is inclined; and

FIG. 10 is a diagram illustrating positions of the crack and the measurement point.

In accordance with an embodiment, a deformation detecting device comprises a vibration module, a transmission time measurement module, an inclination measurement module and a determination module. The vibration module vibrates a first point of a measuring plane of a measured object in a non-contact manner. The transmission time measurement module measures transmission time of vibration from the first point to a second point of the measuring plane in a non-contact manner. The inclination measurement module measures an inclination of the measuring plane to a reference surface in a non-contact manner. The determination module determines presence/absence of deformation in the measured object by comparing the transmission time with reference transmission time serving as transmission time of vibration from the first point to the second point in a case in which there is no inclination of the measuring plane and corrects the reference transmission time in response to the inclination of the measuring plane.

Hereinafter, the embodiment is described with reference to the accompanying drawings.

FIG. 1 is a schematic front view of a deformation detecting device 10 .

There is a parametric speaker 800 (vibration module), a lens 431 through which laser light output by a laser Doppler vibrometer 2 A passes, and a lens 430 through which laser light output by a laser Doppler vibrometer 2 B passes on one surface 31 of a housing 3 of the deformation detecting device 10 .

The parametric speaker 800 vibrates a measured object in a non-contact manner. The measured object is made of concrete or mortar. The parametric speaker 800 includes a plurality of transducers 801 serving as ultrasonic piezoelectric elements (in the present embodiment, eight transducers 801 ). The transducers 801 are arranged annularly and closely around an optical axis of the laser light emitted by the laser Doppler vibrometer 2 A, that is, around the lens 431 . Each transducer 801 has a directivity of 60-70 degrees.

As shown in FIG. 1 , if the transducers 801 are arranged closely in such a manner that the transducers 801 contact with each other, directivity of an ultrasonic wave output by the parametric speaker 800 becomes narrow overall, and the ultrasonic wave is emitted to a measuring plane 4 ( FIG. 3 ) in almost a straight line. A central axis of the ultrasonic wave output by the parametric speaker 800 passes the center of the plurality of the transducers 801 , and is coincident with the optical axis of the lens 431 . A distance between the optical axis of the lens 431 and the optical axis of the lens 430 is L 0 . The distance L 0 is a reference transmission distance L 0 of ultrasonic wave transmission, and becomes a setting value determined according to arrangement of optical parts of the laser Doppler vibrometers 2 A and 2 B.

FIG. 2 is a diagram illustrating a modification of arrangement of the transducers 801 .

A total of four transducers 801 may be arranged on the left, right, top and bottom of the lens 431 in FIG. 2 .

FIG. 3 is a schematic diagram illustrating the parametric speaker 800 and the laser Doppler vibrometers 2 A and 2 B.

The parametric speaker 800 outputs the ultrasonic wave towards a measurement point P 1 (first point) of the measuring plane 4 of the measured object to vibrate the measurement point P 1 .

The laser Doppler vibrometer 2 A outputs a laser from a semiconductor laser 1401 , and irradiates the measurement point P 1 with the laser via the lens 431 . The semiconductor laser 1401 includes a laser element 1402 and a photodiode 1403 which is arranged adjacent to the laser element 1402 and integrally packaged with the laser element 1402 . The laser light reflected by the measurement point P 1 enters the laser element 1402 .

The laser Doppler vibrometer 2 A which is the self-mixing interference type uses interference of the output laser light and reflected light at the measurement point P 1 to measure vibration of the measurement point P 1 in a non-contact manner and to measure a distance LMI from the one surface 31 of the housing 3 serving as a reference surface to the measurement point P 1 in a non-contact manner. Hereinafter, the one surface 31 of the housing 3 is recorded as a reference surface 31 . The reference surface 31 is used to calculate the distance LMI and a distance LMr which is described later, and may be set at a proper position.

The laser Doppler vibrometer 2 B condenses laser light output by a semiconductor laser 401 to a galvanometer mirror 420 through an optical unit 408 . The semiconductor laser 401 includes a laser element 402 and a photodiode 403 . After being emitted to a measurement point P 2 (second point) via the lens 430 , the laser light reflected by the galvanometer mirror 420 becomes reflected light and enters the laser element 402 .

The laser Doppler vibrometer 2 B which is the self-mixing interference type uses interference of the output laser light and the reflected light at the measurement point P 2 to measure vibration of the measurement point P 2 in a non-contact manner and to measure the second distance LMr from the one surface 31 of the housing 3 to the measurement point P 2 in a non-contact manner.

The galvanometer mirror 420 is rotationally driven about an x axis and a y axis by an x axis actuator for driving about x axis and a y axis actuator for driving about y axis. If setting the measuring plane 4 as an X-Y plane orthogonal to each other, a CPU ( FIG. 4 : determination module) described later can set the measurement point P 2 at an arbitrary coordinate (X, Y) on the X-Y plane by controlling the x axis actuator and the y axis actuator.

FIG. 4 is a block diagram illustrating principles of distance measurement and vibration measurement of the laser Doppler vibrometer 2 A. The principles of the distance measurement and the vibration measurement of the laser Doppler vibrometer 2 A are identical to that of the laser Doppler vibrometer 2 B, and thus the descriptions of the principles of the distance measurement and the vibration measurement of the laser Doppler vibrometer 2 B are omitted.

Firstly, the principle for determining a timing at which the measurement point P 1 is vibrated by the ultrasonic wave.

The laser element 1402 of the semiconductor laser 1401 is driven and controlled by the CPU at a constant current via a current driver 1404 . The laser element 1402 which is the edge emitting type outputs the laser light from one end surface. The laser light output by the laser element 1402 is emitted to the measurement point P 1 via the lens 431 . The reflected light reflected by the measurement point P 1 enters the laser element 1402 via the lens 431 .

The laser element 1402 outputs a back beam from an end surface opposite to the one end surface from which the laser light is output in a direction opposite to the output direction of the laser light. An optical axis of the back beam is located on the same straight line as the optical axis of the laser light. The photodiode 1403 receives the back beam.

After an output signal of the photodiode 1403 is converted from a current to a voltage and amplified via an amp 1405 , noise of high-frequency components is cut by a low pass filter 1406 .

If the measuring plane 4 vibrates, Doppler shift is generated, and a frequency of the reflected light slightly changes. With the reflected light entering the laser element 1402 , the influence of the change of the frequency of the reflected light appears on the back beam. The output signal which is output from the photodiode 1403 and passes the low pass filter 1406 is a beat signal 1409 . By monitoring the beat signal 1409 , whether the Doppler shift is generated can be determined, and the timing at which the measurement point P 1 is vibrated by the ultrasonic wave can be determined. Further, by carrying out Fourier transform on the output signal of the low pass filter 1406 through an FFT 1407 , a power spectrum of the back beam can be obtained.

Next, the measurement principle of the distance from the reference surface 31 to the measuring plane 4 is described.

The output signal of the photodiode 1403 is input to comparators 1413 and 1414 via the amp 1405 . A gate section 1415 and a counter 1416 are arranged at the rear stage of the comparators 1413 and 1414 .

FIG. 5 is a diagram schematically illustrating output of the photodiode 1403 . In FIG. 5 , the horizontal axis indicates time, and the vertical axis indicates the output of the photodiode 1403 .

In a case in which an output voltage of the photodiode 1403 is greater than a reference voltage TH 1 , an output voltage of the comparator 1413 becomes High, and in a case in which the output voltage of the photodiode 1403 is smaller than the reference voltage TH 1 , the output voltage of the comparator 1413 becomes Low. At a timing T 1 at which the laser element 1402 starts the output of the laser light, as the output of the photodiode 1403 is increased corresponding to a light receiving quantity of the back beam, the output voltage of the comparator 1413 becomes High.

In a case in which the output voltage of the photodiode 1403 is greater than a reference voltage TH 2 , an output voltage of the comparator 1414 becomes High, and in a case in which the output voltage of the photodiode 1403 is smaller than the reference voltage TH 2 , the output voltage of the comparator 1414 becomes Low. If the reflected light entering the inside of the laser element 1402 resonates with the output laser light in the laser element 1402 , the output of the back beam is increased.

FIG. 6 is a timing chart illustrating operation principles of the gate section 1415 and the counter 1416 .

In a case in which the output of the comparator 1413 is High and the output of the comparator 1414 is Low, the gate section 1415 outputs “High”, and in a case of other combinations of the output of the comparators 1413 and 1414 except that, the gate section 1415 outputs “Low”. In other words, the gate section 1415 outputs “High” during a period from a moment the laser light is output to a moment the laser light returns after being reflected by the measurement point P 1 .

The counter 1416 measures clocks and calculates flight time of the laser light while the output of the gate section 1415 is High.

The CPU calculates a distance to the measurement point P 1 on the basis of a measurement value of the counter 1416 . The CPU calculates “speed of light*measuring time/2”, and calculates the distance LMI from the reference surface 31 to the measurement point P 1 on the basis of the distance.

According to the above, the CPU can measure the distance LMI to the vibrating measurement point P 1 with the laser Doppler vibrometer 2 A. Further, the CPU can measure the timing at which the measurement point P 1 is vibrated by monitoring the beat signal 1409 . Similarly, the CPU can measure the distance LMr from the reference surface 31 to the measurement point P 2 with the laser Doppler vibrometer 2 B. The CPU can measure the timing at which the ultrasonic wave is transmitted from the measurement point P 1 to the measurement point P 2 by monitoring the beat signal 1409 .

A transmission time measurement module for measuring transmission time of vibration from the measurement point P 1 to the measurement point P 2 of the measuring plane 4 in a non-contact manner is constituted by the laser Doppler vibrometers 2 A and 2 B and the CPU.

Hereinafter, a deformation detecting processing of the CPU is described with reference to FIG. 3 and the flowchart of FIG. 7 .

Firstly, the deformation detecting device 10 is arranged in such a manner that the laser light to the measurement point P 1 vertically enters the measuring plane 4 of a concrete wall in integrity with no crack. The CPU irradiates the measurement points P 1 and P 2 with the laser light through the laser Doppler vibrometers 2 A and 2 B, and measures the distances LMI and LMr to the measurement points P 1 and P 2 (Act 1 ). At this time and before a processing in Act 10 described later, the galvanometer mirror 420 is set at an angle at which the output laser light of the laser Doppler vibrometer 2 A and that of the laser Doppler vibrometer 2 B are parallel to each other.

A user adjusts the deformation detecting device 10 so that the distances LMI and LMr are equal and the measuring plane 4 is not inclined. No inclination is the most ideal state; however, as there is also a case in which it is difficult to realize no inclination according to the present state, the gesture of the deformation detecting device 10 is adjusted so that the inclination of the measuring plane 4 is within a predetermined range.

The CPU vibrates the measurement point P 1 with the parametric speaker 800 . The CPU measures transmission time T 0 of the ultrasonic wave from a moment the vibration is detected at the measurement point P 1 to a moment the vibration is detected at the measurement point P 2 (Act 2 ). The transmission time T 0 of the ultrasonic wave in the measuring plane 4 in integrity with no crack is set as reference transmission time T 0 . A transmission distance of the ultrasonic wave serving as a distance between the measurement points P 1 and P 2 is L 0 which is the setting value.

The CPU stores the reference transmission time T 0 in a memory (Act 3 ).

FIG. 8 is a diagram illustrating a transmission path of the ultrasonic wave in a case in which there is a crack in the measuring plane 4 .

As the ultrasonic wave cannot be transmitted to the crack part, in a case in which there is the crack in the measuring plane 4 , the ultrasonic wave is transmitted circuitously to the top in the depth D direction of the crack and finally reaches the measurement point P 2 of the laser Doppler vibrometer 2 B as indicated by one dotted lines.

In a case in which there is the crack in the measuring plane 4 , as the ultrasonic wave cannot be transmitted to the surface of the measuring plane 4 , the ultrasonic wave is transmitted at a distance longer than the distance L 0 between the measurement points P 1 and P 2 . As the speed of the ultrasonic wave which is transmitted in the measured object is almost constant, in a case in which there is the crack in the measuring plane 4 , transmission time t is greater than the reference transmission time T 0 .

After the reference transmission time T 0 in the measuring plane 4 in integrity is measured in advance, the transmission time t in the measuring plane 4 of the measured object is measured. If the transmission time t is greater than the reference transmission time T 0 , it can be determined that there is the crack in the measuring plane 4 .

FIG. 9 is a diagram illustrating the distances LMI and LMr to the measurement points P 1 and P 2 in a case in which the measuring plane 4 is inclined. That the measuring plane 4 is inclined means that the distances LMI and LMr from the reference surface 31 to the measurement points P 1 and P 2 are different.

In a case in which the measuring plane 4 is inclined, a transmission distance L 00 of the ultrasonic wave between the measurement points P 1 and P 2 is larger than the transmission distance L 0 at the time the reference transmission time T 0 is acquired. Thus, in a case in which the measuring plane 4 is inclined, even if there is no crack in the measuring plane 4 , the transmission time t becomes greater than the reference transmission time T 0 as the transmission distance L 00 is larger than the transmission distance L 0 at the time the reference transmission time T 0 is acquired. Thus, if the measured transmission time t and the reference transmission time T 0 are compared, even if there is no crack between the measurement points P 1 and P 2 , there is a possibility of mistakenly determining that the crack exists.

Thus, the CPU detects an inclination θ of the measuring plane 4 and corrects the reference transmission time T 0 according to the detected inclination θ to suppress the mistaken determination.

Firstly, the CPU measures the distances LMI and LMr from the reference surface 31 to the measurement points P 1 and P 2 . If the distances LMI and LMr are different, the CPU determines that the measuring plane 4 is being inclined and calculates the inclination θ of the measuring plane 4 . The CPU calculates the inclination θ of the measuring plane 4 with the following equation: tan θ==P 2 P 2 ′/P 1 P 2 ′=(LMr−LMI)/L 0 . The P 2 ′ indicates a position of the measurement point P 2 in a case in which the measuring plane 4 is not inclined.

An inclination measurement module for measuring the inclination θ of the measuring plane 4 to the reference surface 31 in a non-contact manner is constituted by the laser Doppler vibrometers 2 A and 2 B and the CPU. A first distance measurement module for measuring the distance LMI from the reference surface 31 to the measurement point P 1 in a non-contact manner is constituted by the laser Doppler vibrometer 2 A and the CPU. A second distance measurement module for measuring the distance LMr from the reference surface 31 to the measurement point P 2 in a non-contact manner is constituted by the laser Doppler vibrometer 2 B and the CPU.

In a triangle P 1 P 2 ′P 2 , the following equation is established: L 00 =L 0 /cos θ due to L 0 /L 00 =cos θ. Thus, the reference transmission time is in proportion to the distance, and thus it is understood that the corrected reference transmission time T 00 becomes T 0 /cos θ.

The CPU calculates the corrected transmission distance L 00 with the equation “L 00 =L 0 /cos θ”. The CPU calculates the corrected reference transmission time T 00 with the equation “T 00 =T 0 /cos θ”. The CPU stores the corrected transmission distance L 00 and the corrected reference transmission time T 00 in the memory (Act 4 ).

The CPU vibrates the measurement point P 1 with the parametric speaker 800 , and measures the transmission time t at the measurement point P 2 (Act 5 ). The CPU stores the transmission time t in the memory (Act 6 ).

The CPU compares the transmission time t with the corrected reference transmission time T 00 (Act 7 ). If the transmission time t is greater than the reference transmission time T 00 , the CPU determines that there is the crack (Act 8 ). If the transmission time t is equal to or smaller than the reference transmission time T 00 , the CPU determines that there is no crack (Act 9 ). Furthermore, in consideration of the noise included in the transmission time t, if the transmission time t is not greater than the reference transmission time T 00 by a predetermined value, the CPU may determine that there is no crack.

According to the above, the CPU determines presence/absence of the crack between the measurement points P 1 and P 2 .

FIG. 10 is a diagram illustrating positions of a crack and the measurement point P 2 .

In FIG. 10 , a crack is represented by a thick black line for convenience; however, a crack can be visually confirmed in some cases but cannot be visually confirmed in other cases. The deformation detecting device 10 can also detect a crack which cannot be visually confirmed. A crack does not always extend linearly but extends while heading a continuously changing direction in some cases as shown in FIG. 10 .

A coordinate (x0, y5) is the measurement point P 1 irradiated by the ultrasonic wave and the laser light. The CPU, for example, firstly irradiates (x5, y5) serving as the measurement point P 2 with the laser light for detecting the transmission of the ultrasonic wave, and then carries out the foregoing determination processing in Act 4 ˜Act 9 of the presence/absence of a crack 900 . The CPU determines whether or not there is the crack 900 between (x0, y5) of the measurement point P 1 and (x5, y5) of the measurement point P 2 .

After that, the CPU determines whether or not a completion condition, for example, whether all the measurement of a plurality of the set measurement points P 2 is completed, is met (Act 10 ). If it is determined that the completion condition is not met (NO in Act 10 ), the CPU drives the galvanometer mirror 420 to change the measurement point (Act 11 ).

The CPU moves the measurement point P 2 to, for example, (x1, y5), and then caries out the determination processing in Act 5 ˜Act 9 of the presence/absence of the crack 900 again. In this way, this time, the CPU determines whether or not there is the crack between (x0, y5) of the measurement point P 1 and (x1, y5) of the measurement point P 2 .

As the angle of the galvanometer mirror 420 changes, the distance between the measurement points P 1 and P 2 changes. In FIG. 9 , if the measurement point moves from P 2 to P 2 ″, the size of the measured distance L 00 varies. As a variation quantity of the measured distance L 00 corresponds to the angle of the galvanometer mirror 420 , the CPU corrects the measured distance L 00 and the reference transmission time T 00 in response to the angle of the galvanometer mirror 420 through a predetermined conversion equation. Then, the CPU compares the reference transmission time T 00 corrected in response to the angle of the galvanometer mirror 420 with the transmission time t at the measurement point P 2 of the movement destination to determine the presence/absence of the crack.

In this way, the CPU can detect the distribution of the crack 900 in the measuring plane 4 by scanning the measurement point P 2 .

The CPU ends the measurement if the completion condition is met as all the measurement of the plurality of the set measurement points P 2 is completed (YES in Act 10 ). Further, the change method of the position of the measurement point P 2 is optional.