JP2005308486A - Vibration sensor, inspection device, and inspection method of buried pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To acquire highly accurate data, while keeping a simple constitution of the whole inspection device, by preventing with a simple constitution, entrance of a noise into a vibration sensor for receiving an elastic wave signal, when inspecting a buried pipe by an impact elastic wave method. <P>SOLUTION: A vibration sensor body 10 is supported by an elastic support tool 15 in a case 11, and a contactor 101 of the vibration sensor body 10 is projected to the outside of the case 11, and a pressure sensor 14 generating a contact pressure control signal by transmission of a contact pressure of the contactor 101 through the support tool 15 is provided in the case 11. Consequently, a noise from the case 11 side can be reduced or blocked by adjustment of a spring constant of the elastic support tool 15 or by addition of a vibration isolation member such as rubber, a foaming material or a gel material to the elastic support tool 15, to thereby acquire accurate received wave data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an inspection apparatus used when inspecting an embedded pipe by a shock elastic wave method, a vibration sensor as a main part of the inspection apparatus, and a method for inspecting an embedded pipe using the inspection apparatus.

Recently, in sewage pipes and agricultural water pipes, accidents such as depression and water leakage are increasing due to corrosive wear and breakage of buried pipes over time. For this reason, appropriate deterioration diagnosis and appropriate repair / updating based on the diagnosis result are required.
In this deterioration diagnosis of sewage pipes and agricultural water pipes, in general, in order to determine the order of repair and reconstruction works and the construction method, ranking of the degree of deterioration between the element areas constituting the survey basin and quantitative It is necessary to grasp the progress of the deterioration level.
Conventionally, visual inspection or visual inspection is performed using a TV camera, and the physical properties of the sample obtained by removing the core are investigated as necessary. It is difficult to accurately and quantitatively grasp the degree of deterioration. Or, in order to collect quantitative data, it is necessary to remove a large number of cores, and the strength of the healthy tubular body is inevitably lowered, and the work cost is inevitably increased.

As a nondestructive test method, an ultrasonic method, a percussion method, and a shock elastic wave method are known.
However, in the ultrasonic method, since the ultrasonic wave as an input wave has a high frequency and low energy, it is difficult for the input wave to propagate through the concrete, and it is not suitable for the inspection of concrete products.
In the sounding method, since the signal is received by a non-contact acoustic device such as a microphone, it is easily affected by ambient noise, and is easily affected by reflection on the back side of the hitting point.・ There are inconveniences such as easy individual differences in diagnosis, and there is a problem in diagnosis accuracy.
The shock elastic wave method is a method in which an elastic wave is input to an object to be inspected by mechanical impact such as hitting, a frequency spectrum of a waveform received by a vibrator in contact with the object to be inspected, and analysis and determination of the frequency spectrum is performed. The present applicant has already proposed a diagnosis system for buried pipes using the shock elastic wave method. (For example, Patent Document 1, Non-Patent Document 1, Non-Patent Document 2, etc.)

JP 2004-028976 A Minaki, Kamada, Nozaki, Funabashi, Basic research on deterioration diagnosis method of concrete sewer pipes by elastic wave, Annual report of concrete engineering, 2002, VOL24, No1, p. 1539-1544

FIG. 7 shows an inspection apparatus used for the buried pipe inspection method using the shock elastic wave method proposed by the present applicant.
In FIG. 7, 20 ′ is a carriage, 21a ′ is a first arm attached to the carriage 20 ′, A ′ is a vibration sensor attached to the tip of the first arm 21a ′, and 21b ′ is a second arm attached to the carriage 20 ′.
Arm B ′ is a hammer attached to the tip of the second arm 21b ′, 4 ′ is a control unit, 5
'Is a computer that performs operation, data recording and analysis. By operating the first arm, the vibration sensor is brought into contact with the inner surface of the tube to be inspected, then the second arm is operated, and the hammer is further operated to operate the inner surface of the tube. , The elastic wave generated by this blow is received by the vibration sensor,
The frequency spectrum of the received waveform is obtained by a fast Fourier transform program, and the deterioration diagnosis of the buried pipe is performed based on the analysis determination of the frequency spectrum.

If the input at the input point is the impulse I shown in FIG. 8 (a), the impulse I arrives at the input point through reflection and transmission at a defect portion such as reflection at the tube end and crack, The incoming wave x involves the bending rigidity EI of the tube, the damping coefficient c, the elapsed time t, the distance L between the input point and the receiving point, and the like.

で表すことができる。 x = x (EI, c, L, t)
If the input elastic wave is f (t) as shown in FIG.
Output X is

It can be expressed as

When the frequency spectrum of the received wave X is obtained, a complicated distribution pattern is formed due to reflection at the above-described tube end or defect portion, the maximum peak occurs at the natural vibration frequency, and cracks are present in the tube. Due to the decrease in rigidity, the natural vibration frequency (maximum peak frequency) shifts to the low frequency side, the ratio of (low frequency component) / (high frequency component) of the same frequency spectrum increases, and the maximum peak value decreases. In particular, when the crack of the pipe body is in the direction of the pipe axis, the divided concrete parts with different masses vibrate separately due to impact, but the interaction in the coupled vibration affects the damping time. The number of peaks having a predetermined intensity or more is reduced, information according to the degree of deterioration and the pattern of cracks can be obtained, and quantitative deterioration diagnosis can be performed.

In the inspection apparatus described above, the arm is tilted by the gear mechanism, and rattling due to gear play is inevitable, and a collision sound is generated at the rattling portion by the vibration wave of the vibration sensor, and the elasticity generated by the collision sound or hammering. There is a problem that the wave is propagated to the vibration sensor through the arm, and this propagation wave becomes noise and causes a measurement error.
For this reason, although the anti-vibration mechanism is incorporated in the arm, the structure of the inspection apparatus is complicated and expensive.

An object of the present invention is to maintain a simple configuration of the entire inspection apparatus by preventing noise from entering a vibration sensor that receives an elastic wave signal with a simple configuration when an embedded tube is inspected by a shock elastic wave method. It is to obtain highly accurate data.

In the vibration sensor according to the present invention, the vibration sensor main body is supported by the elastic support in the case, the contact of the vibration sensor main body is cued out of the case, and the contact pressure of the contact is transmitted through the support jig. A pressure sensor that generates a contact pressure control signal is provided in the case.

The inspection apparatus according to the present invention includes a support means for supporting the vibration sensor according to claim 1 and a support means for supporting the hitting tool mounted on a gantry, and a contactor according to a control signal from a pressure sensor in the vibration sensor. An operating mechanism and a striking tool operating mechanism for setting the contact pressure to a predetermined pressure are provided.

According to the buried pipe inspection method of the present invention, the inspection apparatus according to claim 2 is introduced into the inspection pipe body of the embedded pipe, and the vibration sensor support means is operated to place the contact on the inner surface of the inspection pipe body at a predetermined pressure. After that, the hammer support means is operated to strike the inner surface of the tube to be inspected, and the frequency spectrum of the waveform received by the vibration sensor body is measured. It is characterized by performing deterioration diagnosis.

In the vibration sensor according to the present invention, the pressure sensor for setting the contact pressure of the contact of the vibration sensor main body is provided in the sensor case, and it is not necessary to provide the pressure sensor in the vibration sensor support means. The structure of the means can be simplified. In addition, noise from the vibration sensor support means side can be reduced or blocked by adjusting the spring constant of the elastic support jig or by adding a vibration isolator such as rubber, foam, or gel to the elastic support jig. Therefore, it is not necessary to provide a vibration isolation mechanism in the vibration sensor support means, so that the structure of the sensor support means can be simplified.
In the inspection apparatus according to the present invention, propagation of a part of the elastic wave generated by hammer hit to the vibration sensor contact through the vibration sensor support means and the hammer support means is reduced or reduced by the elastic support jig in the vibration sensor. The elastic support jig in the vibration sensor reduces the propagation of part of the received elastic wave to both support means, which can be prevented, and can be a source of collision noise in the play of the gear mechanism of the vibration sensor support means and hammer support means. In addition, since it is possible to obtain accurate received wave data, it is not necessary to provide a vibration isolation mechanism in the vibration sensor support means and the hammer support means, so that the structure of these support means can be simplified.
In the buried pipe inspection method according to the present invention, an accurate frequency spectrum can be obtained from a noise-free vibration wave, and the deterioration diagnosis of the buried pipe can be accurately performed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 (a) is a side view showing a part of a vibration sensor according to an embodiment of the present invention in cross section, FIG. 1 (b) is a cross-sectional view of FIG. (C) is the same as (a) in FIG.
FIG. 1C is a top view of the embodiment.
In FIG. 1, reference numeral 11 denotes a case, which includes a 111 sensor main body storage chamber and a pressure transmission jig storage chamber 112. Reference numeral 12 denotes a pressure transmission jig accommodated in the pressure transmission jig accommodation chamber 112 of the case 11 so as to be slidable in the vertical direction, and is constituted by a six-sided wall solid rigid against compression. Reference numeral 13 denotes a lower lid fixed to the lower end of the case with a screw or the like, and a pressure sensor 14 such as a load cell.
The contact 141 of the pressure sensor 14 is in contact with the lower surface of the pressure transmission jig 12. Reference numeral 10 denotes a vibration sensor main body. The screw-type contact 101 can be attached and detached, and the protruding length of the contact 101 is set to a predetermined length by exchanging the contacts 101 having different lengths.
Reference numeral 15 denotes an elastic support jig, which has a cylindrical shape and is placed on the upper surface of the pressure transmission jig 12. The vibration sensor main body 10 is inserted into the cylindrical elastic support jig 15, and the upper side of the vibration sensor main body 10. A flange portion 102 (which can be provided by screwing a nut) is supported at the upper end of the support jig 15, and the vibration sensor main body lower end portion 103 is inserted into the hole 121 on the upper surface of the pressure transmission jig. 1
04 is an electric cable of the vibration sensor main body 10, 142 is an electric cable of the pressure sensor 14, and is pulled out from the case 11 through the cable insertion hole 122 of the pressure transmission jig 12.

The cylindrical elastic support jig 15 includes a spring whose spring constant is adjusted as shown in FIG. 2A in order to reduce or block the propagation of vibration between the case 11 and the vibration sensor body 10. A cylindrical jig made of buffer, a cylindrical jig made of a buffer material such as a rubber cylinder or a foamed resin cylinder shown in FIG. 2B, and buffered at the upper or lower end or upper and lower ends of the metal cylinder piece 150 shown in FIG. It is preferable to use a material in which the material cylinder pieces 151 and 152 are fixed.

In FIG. 1, reference numeral 16 denotes an upper lid fixed to the upper end of the case 11 with a screw or the like, and a hole 161 smaller than the outline of the flange 102 of the vibration sensor 10 is provided, from which the contact of the vibration sensor main body 10 is provided. 101 is cued, and the sensor body 10 can move up and down following the vertical displacement of the contact point of the contact 101.

The vibration sensor main body 10 may be any system that picks up vibration acceleration, vibration speed, and vibration displacement, and the sensor element is a resistance strain gauge, a semiconductor gauge using the piezoelectric effect, a piezoelectric such as a piezoelectric ceramic. A type acceleration pickup can be used.
The vibration sensor according to the present invention is a corrosion-resistant metal in a portion that is easy to touch sewage when used in a sewage pipe or an agricultural water pipe, in particular, the upper lid 16, the contact 101 of the vibration sensor, the case 11, and the lower lid 13. For example, it is preferable to use an aluminum alloy or SUS.

FIG. 3A is a side view showing an embodiment of the inspection apparatus according to the present invention.
In FIG. 3 (a), reference numeral 20 denotes a carriage, as shown in FIG. 3 (b) so that it can be easily carried into the pipeline through the orthogonal space between the manhole and the pipeline. It can be folded. 21a is a first arm attached to the carriage as a vibration sensor support means, and 21b is a second arm as a hammer support means. The lower ends of the first arm are connected to the servo motor shaft via a gear mechanism, and tilted by driving the servo motor. It is possible. A is a vibration sensor according to the present invention, and is fixed to the tip of the first arm 21a. B is an impulse hammer as a hitting tool, which includes a spring-type or hydraulic-type impactor 22 and is fixed to the tip of the second arm 21b.
The arm can be moved up and down by a rack mechanism or a cylinder mechanism.
Also, distance between hammer hit point and vibration sensor contact point (distance between input point and output point)
In order to adjust the angle, the arm can also be movable and controlled in the horizontal direction.
In place of the arm, if the vibration sensor can be supported and the contact can be brought into contact with a predetermined position on the inner surface of the tube, and the hammer can be supported and the predetermined position on the inner surface of the tube can be hit, an appropriate support means is used. it can.
As the hitting tool, hammers, steel balls, etc. can be used in addition to the impulse hammer. However, it is desirable to always apply the hits with the same force. For example, hammers, steel balls, etc. are hit using a Schmitt hammer, spring, piston, etc. It is desirable to use a steel ball or the like that drops from a certain height. When using an impulse hammer, it is desirable to measure the numerical data of the input information and reflect it during analysis.

FIG. 4 shows the use state of this inspection apparatus.
In FIG. 4, first, the first arm 21a is tilted to bring the contact 101 of the vibration sensor A into contact with the inner surface of the pipe, and the first pressure signal of the pressure sensor of the vibration sensor A (reference numeral 14 in FIG. One arm 21a is controlled to set the contact pressure of the contact 101 to a predetermined pressure. Next, the second arm 21b is tilted to a predetermined height, and the impactor 22 of the hammer B is operated at the predetermined height to strike the inner surface of the tube to generate an input elastic wave. The contact 1 of the vibration sensor A
01 receives the elastic wave.
In the vibration sensor according to the present invention, as shown in FIG.
Elastic support jig 15 having an excellent vibration absorbing function between 0 and case 11, for example, a spring cylindrical jig whose spring constant is adjusted, a cylindrical jig made of a cushioning material such as a rubber cylinder or a foamed resin cylinder, a metal cylinder Since the composite jig | tool which fixed the cylinder piece made from a buffer material is interposed in the upper end or lower end or upper and lower ends of the piece, FIG.
In this case, it is possible to prevent the hammering vibration of the hammer B from propagating to the vibration sensor main body through the arms 21b and 21a, and it is possible to receive only the elastic wave propagating through the tubular body to the vibration sensor main body and to accurately include no noise. Can receive input. In this case, as shown in FIG. 1A, the electric cable 104 of the vibration sensor main body 10 is drawn out of the case 11 through the hole 122 provided in the pressure transmission jig 12, and is electrically connected to the elastic support jig 15. Since there is no need to provide a cable lead-out hole, the vibration absorbing function of the support jig 15 can be satisfactorily secured, and accurate input vibration can be secured.

In the above, if the distance between the output point and the input point is short, the distance until the elastic wave reflects the tube defect point and reaches the input point becomes long, the attenuation between them becomes large and the defect information becomes weak. Therefore, the distance between the output point and the input point is preferably ¼ or more of the tube length.

In FIG. 4, the carriage can be separated at the middle folding point, and the distance between the vibration sensor and the hammer can be set to a desired value. In this case, propagation of the hammer hitting sound to the vibration sensor body through the path of the hammer → second arm → cart → tube → cart → first arm is blocked by the elastic support jig. Only the propagating elastic wave can be received by the vibration sensor body, and an accurate input including no noise can be received.

In the above, the natural vibration frequency component in the elastic wave received by the vibration sensor exhibits the maximum peak value (hereinafter, the frequency exhibiting the maximum peak value is also referred to as the maximum peak frequency), and the inspection tube has a defect such as a crack. If it exists, the maximum peak frequency is shifted to the low frequency side due to a decrease in the bending rigidity of the tube. For the same reason, the ratio of (low frequency component) / (high frequency component) is also increased. Further, if there is a defect such as a crack in the tube to be inspected, the vibration is difficult to propagate and the intensity value of the maximum peak is reduced. In addition, if there are circumferential cracks in the pipe body, the divided concrete parts with different masses vibrate separately by impact, but the damping time is affected by the interaction in the coupled vibrations. The number is reduced.

In this case, the output waveform of the elastic wave changes depending on the environmental conditions such as the water level in the buried pipe and the earth pressure of the buried pipe. This is because the damping coefficient c and the substantial bending rigidity EI in the basic equation [Equation 1] described above. It is clear if the change of (when the earth pressure increases, the degree of restraint of the pipe increases and the rigidity EI increases substantially) is assumed.
However, according to the results of earnest experiments by the present inventors, the peak frequency, the ratio of (low frequency component) / (high frequency component), and the number of peaks do not change substantially, and the peak value of the received elastic wave decreases. (This is because part of the output elastic wave is released into the water in the pipe in proportion to the rise in the pipe water level, and part of the output elastic wave is released in the cover soil in proportion to the rise in the soil pressure on the pipe. Estimated).
According to the experimental results, the correction coefficient a at the water level x% with respect to the peak value of the output elastic wave of the concrete fume having a nominal diameter of 250 mm based on the type 1 of JISA 5303 B is:

[Formula 2] a = 1 / (− 0.005x + 1)
The correction coefficient b at the covering soil thickness ym is given by

[Formula 3] b = 1 / (− 0.28y + 1.14)
Given in.

In order to perform the deterioration diagnosis of the buried pipe by the buried pipe inspection method according to the present invention, an elastic wave is input to each of the joined pipes, the received elastic wave is recorded with respect to the input, and the received elastic wave is A frequency spectrum is obtained by processing with a Fourier transform program, and this frequency spectrum is analyzed to determine deterioration. However, in order to unify the diagnostic criteria, the positions of the input, the input point, and the output point and the distance are made the same as much as possible.
As is clear from the above equation 1, the output varies depending on the level (crest value) of the input f (t). Therefore, in order to eliminate the influence of the input level difference, (frequency spectrum of output wave) /
It is effective to analyze the transfer function given by (frequency spectrum of input wave).
The time length of the input elastic wave by the impulse hammer is approximately 120 μs. The measurement time of the received elastic wave is usually 800 × 10 μs. The frequency of the frequency spectrum is 0.5-10
kHz (low frequency range of 0.5 kHz or less is cut to eliminate noise).

In order to perform the deterioration diagnosis of the buried pipe by the buried pipe inspection method according to the present invention, for example, the flow shown in FIG. In this case, if a shock elastic wave test of one tube is performed,
The inspection apparatus is transferred to the next tube, but if the depression is severe, it is determined that the deterioration is severe without performing a shock elastic wave test.
In FIG. 4, 3 indicates a TV camera, and the degree of depression is monitored by the TV camera, and the inspection apparatus is shifted while monitoring the inner surface of the pipeline. Reference numeral 4 denotes a control unit, and 5 denotes a personal computer or TV camera monitor for inputting operation signals, data recording, and fast Fourier transform.
In order to diagnose the deterioration of buried pipes, first, each pipe body of the buried pipe line is subjected to a shock elastic wave test using the inspection apparatus according to the present invention, and the input elastic wave received by the vibration sensor is sent to a personal computer. Save and Fourier transform the input elastic wave with fast Fourier transform software to obtain the transfer function of the frequency spectrum. Measure the buried depth y (m), measure the pipe water level x (%), calculate the correction coefficient by the above formulas 2 and 3, and correct the buried depth and the pipe water level. The transfer function of the corrected frequency spectrum is obtained.
The transfer function of this corrected frequency spectrum is analyzed, and the spectrum intensity value of the maximum peak is 4
When the number of peaks of 0% or more is obtained and the number of peaks is 2 or less (see (b) of FIG. 6), it is diagnosed that there is an axial crack, and when the number of peaks is 3 or more (( C) (see (d) of FIG. 6), the intensity value of the maximum peak is analyzed and compared with the frequency spectrum transfer function (see (a) of FIG. 6) of the healthy tube obtained in advance. If the intensity value is significantly reduced (see (c) in FIG. 6), it is diagnosed that there is a circumferential crack, and if the decrease in the intensity value of the maximum peak is small (see (d) in FIG. 6), the tube Diagnosis of thickness reduction.

In addition, the transfer function of the frequency spectrum shown to (i)-(d) of FIG.
3B type 1 type nominal fume pipe with a nominal diameter of 250 mm and pipe length of 2 m, the distance between the input point and the receiving point is 1950 mm, an impulse hammer is used for the hammer, and GH-313A made by Keyence is used for the vibration sensor body Used, rubber is used for the elastic support, GA-245 manufactured by Keyence Co. is used for the receiving amplifier, and NR-200 manufactured by Keyence Co. is used for the data logger.
Each of 0 is used, and the fast Fourier transform program is obtained by using an Abu boutique Co., Ltd.

It is drawing which shows the Example of the vibration sensor which concerns on this invention. It is drawing which shows the example from which the elastic supporter in the vibration sensor which concerns on this invention differs. It is drawing which shows the Example of the inspection apparatus which concerns on this invention. It is drawing used in order to demonstrate the inspection method of the buried pipe which concerns on this invention. It is a flowchart in the Example of the inspection method of the buried pipe which concerns on this invention. It is drawing which shows the various frequency spectrum of the received wave in the Example of the inspection method of the buried pipe which concerns on this invention. It is drawing which shows the conventional buried pipe inspection apparatus. It is drawing used in order to show the input in a shock elastic wave method.

Explanation of symbols

A Vibration sensor B Hammer 10 Vibration sensor main body 101 Contact 11 Case 14 Pressure sensor 15 Elastic support 20 Cart 21a Vibration sensor support means 21b Hammer support means

Claims (3)

The vibration sensor body is supported in the case by an elastic support, the contact of the vibration sensor body is squeezed out of the case, and the contact pressure of the contact is transmitted through the support jig to generate a contact pressure control signal. A vibration sensor characterized in that a pressure sensor is provided in the case. The support means for supporting the vibration sensor according to claim 1 and the support means for supporting the impacting tool are mounted on a frame, and the contact pressure of the contact is set to a predetermined pressure by a control signal from the pressure sensor in the vibration sensor. An inspection apparatus comprising an operation mechanism and a striking tool operation mechanism. 3. The inspection apparatus according to claim 2 is introduced into a tube to be inspected of an embedded tube, and the vibration sensor support means is operated to bring the contact into contact with the inner surface of the tube to be inspected at a predetermined pressure. The inner surface of the pipe to be inspected is hit by operating the vibration sensor body to obtain the frequency spectrum of the waveform received by the vibration sensor main body, and the deterioration diagnosis of the buried pipe is performed by analyzing and judging the frequency spectrum. Inspection method.

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