JP2005221324A - Strain measuring instrument and measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a strain measuring instrument and its measuring method for measuring deformation of a measuring object without therein embedding foreign matter such as a sensor. <P>SOLUTION: This strain measuring instrument is equipped with a sound wave generator 13 for letting a sound wave 12 into the measuring object 11, an electromagnetic wave generator 15 for letting an electromagnetic wave 14 into the measuring object 11, an electromagnetic wave receiver 17 for receiving a reflected electromagnetic wave 16, and a signal processor 19 for processing a received signal 18. The deformation of the measuring object can be measured by letting the sound wave and the electromagnetic wave into the object to measure the reflected electromagnetic wave. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a strain measuring apparatus and a measuring method that can remotely measure strains of wind turbine blades for wind power generation, aircraft structures, concrete structures, and the like.

  For example, the blades of wind turbines for wind power generation are often made of a composite material such as FRP (fiber-reinforced plastics). Since the blades of the windmill are distorted by rotation and are damaged by fatigue, the life of the windmill is predicted in order to prevent damage.

  As shown in FIG. 17, conventionally, a strain gauge 3 is provided at the center of the blade 2 of the windmill 1 in the longitudinal direction, and the strain is measured by the measuring instrument 5 through the optical fiber 4. Thus, the lifetime until the composite material was damaged was estimated (Patent Document 1).

JP 2001-183114 A

However, since an optical fiber as a strain sensor is installed on the surface of the blade, air resistance becomes a problem.
Further, for example, the thickness of the structure such as a concrete structure is thick, and the deformation state may not be grasped only by the surface.
In such a case, it is necessary to embed the sensor inside, but there is a problem that it is necessary to destroy the structure in order to embed a strain gauge or the like.

Further, since the optical fiber itself, which is a strain sensor, has a wire diameter of 50 μm, there is a problem that it becomes a defect of the structural material and cannot be embedded separately.
Furthermore, there is a case where the sensor cannot be installed on the surface of the structure like an aircraft made of a composite material.

  In view of the above problems, an object of the present invention is to provide a strain measuring apparatus and a measuring method thereof capable of measuring the deformation without embedding, for example, a sensor that becomes a foreign object in an object to be measured.

  A first invention of the present invention for solving the above-described problem is a sound wave generator that makes a sound wave incident on a measurement object, an electromagnetic wave generator that makes an electromagnetic wave incident on the object to be measured, and a reflected electromagnetic wave. A strain measuring apparatus comprising a receiver and a signal processing device for processing a received signal.

  According to a second aspect of the present invention, there is provided the strain measuring apparatus according to the first aspect, wherein the frequency of the incident sound wave is changed.

  According to a third invention, in the first or second invention, an electromagnetic wave is incident on an object to be measured via a high-frequency lead wire, and a thin lead wire connected to the high-frequency lead wire is provided in the object to be measured. It is in the strain measuring device characterized by being embedded in.

  A fourth invention is the strain measurement apparatus according to the third invention, wherein the object is covered with a metal foil.

  According to a fifth aspect of the present invention, in the third aspect of the invention, the strain measuring apparatus is characterized in that the two thin conductors are embedded in parallel.

  A sixth aspect of the invention relates to the strain measurement apparatus for a rotating body according to any one of the first to fifth aspects, wherein the object to be measured is a rotating body that is rotatably supported with respect to a fixed side. It is in.

  According to a seventh aspect of the present invention, in the sixth aspect of the invention, the rotating body strain measuring apparatus is characterized in that the rotating body is a blade of a wind turbine for wind power generation.

  An eighth invention is a strain measurement method characterized in that a sound wave and an electromagnetic wave are incident on an object to be measured, a reflected electromagnetic wave is received, and the strain is measured by a received signal.

  A ninth invention is the strain measurement method according to the eighth invention, wherein the reflected electromagnetic wave is received while changing the frequency of the incident sound wave.

  According to the present invention, a sound wave and an electromagnetic wave are incident on an object to be measured, and the deformation can be measured by measuring the reflected electromagnetic wave.

  Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiments and examples. In addition, constituent elements in the following embodiments and examples include those that can be easily assumed by those skilled in the art or those that are substantially the same.

[First Embodiment]
A strain measuring apparatus according to a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a conceptual diagram showing a strain measuring apparatus according to the first embodiment.
As shown in FIG. 1, the strain measurement apparatus 10 according to the present embodiment includes a sound wave generator 13 that makes a sound wave 12 incident on a measurement object 11 and an electromagnetic wave generation apparatus that makes an electromagnetic wave 14 incident on the measurement object 11. 15, an electromagnetic wave receiver 17 that receives the reflected electromagnetic wave 16, and a signal processing device 19 that processes the received signal 18.

  In order to make the sound wave 12 and the electromagnetic wave 14 enter the measurement object 11, as shown in FIG. 6, in the case of the sound wave 12, for example, the vibrator 31 is directly attached to the measurement object 11 via the adhesive 32. do it. In the case of electromagnetic waves, for example, the high-frequency lead wire 33 may be directly attached via the horn antenna 34, for example.

According to the present strain measuring apparatus 10, by setting the wavelengths of the sound wave 12 and the electromagnetic wave 14 incident on the measurement object 11, and satisfying the reflection condition of the sound wave, the electromagnetic wave returns as a reflected wave. The reflected electromagnetic wave 16 is received by the electromagnetic wave receiver 17.
Then, from the presence or absence of reflection of the incident electromagnetic wave 14, the sound velocity of the sound wave is calculated from the following equation.

Vac = λ _R × fac / (2n)
Here, Vac is the speed of sound, λ _R is the wavelength of the electromagnetic wave, fac is the frequency of the sound wave, and n is the refractive index of the electromagnetic wave.

Next, the distortion of the measurement object 11 is estimated from the calculated sound speed using the following equation.
ρ = (K + 4 / 3G) / Vac ²
Here, K is the bulk modulus, G is the shear modulus, and ρ is the density.
ε = (ρ−ρ ₀ ) / ρ ₀

In this way, the sound wave and the electromagnetic wave are incident on the inside of the object to be measured 11 which is a structure, and the change in the sound wave due to the distortion of the object to be measured is measured as the change in the reflection frequency of the electromagnetic wave. Can be measured.
As a result, it is no longer necessary to embed a strain measuring device using an optical fiber or the like in the object to be measured 11, and the strain can be measured by so-called contact.

[Second Embodiment]
A strain measuring apparatus according to a second embodiment of the present invention will be described with reference to the drawings.
FIG. 2 is a conceptual diagram showing a strain measuring apparatus according to the second embodiment. In addition, the same code | symbol is attached | subjected about the same member as the measuring apparatus 10 of 1st Embodiment, and the description is abbreviate | omitted.
As shown in FIG. 2, the measuring device 10 according to the present embodiment measures the return time of the reflected electromagnetic wave 16 so that the sound wave generating device 13 and the electromagnetic wave generating device 15 of the first embodiment are positioned coaxially. A time measuring device 20 is provided.
The sound wave 12 and the electromagnetic wave 14 are incident on the same axis, the return time of the reflected electromagnetic wave 16 that is reflected and returned is measured by the time measuring device 20, and the reflection position is calculated from the following equation to obtain the strain distribution.

L = c × t / 2
Here, L is the position of the reflection point, c is the speed of the electromagnetic wave, and t is the return time.
That is, a part of the electromagnetic wave propagating through the object to be measured 11 is reflected by interference with the sound wave. This reflection causes interference at a certain wavelength and returns as a reflected electromagnetic wave. The reflected electromagnetic wave 16 has information on the state (distortion) at the reflection point as a reflection wavelength.
As a result, the strain distribution can be obtained by obtaining the return time and the reflected wavelength at each time.

[Third Embodiment]
A strain measuring apparatus according to a third embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a conceptual diagram showing a strain measuring apparatus according to the third embodiment. In addition, the same code | symbol is attached | subjected about the same member as the measuring apparatus 10 of 1st and 2nd embodiment, and the description is abbreviate | omitted.
As shown in FIG. 3, in the present embodiment, the sound wave 12 incident from the sound wave generator 13 is formed into a pulse shape. A timing device 21 is provided to synchronize the sound wave generator 13 and the electromagnetic wave generator 15.
The difference in reflection time between sound waves and electromagnetic waves is as follows.
t _ac = L / c _ac
t _r = L / c _r
Δt = t _ac −t _r
Here, t _ac is wave propagation time, L is the distance to the measurement target position, the c _ac is the acoustic velocity, t _r electromagnetic wave propagation time, c _r is the velocity of electromagnetic wave, Delta] t is the reflection time difference.

Since the sound wave 12 has a pulse shape, it is possible to prevent disturbance of the signal due to the sound wave in the measurement object 11.
The electromagnetic wave 14 may be similarly pulsed.

[Fourth Embodiment]
A strain measuring apparatus according to a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a conceptual diagram showing a strain measuring apparatus according to the fourth embodiment. In addition, the same code | symbol is attached | subjected about the same member as the measuring apparatus 10 of 1st thru | or 3rd embodiment, and the description is abbreviate | omitted.
As shown in FIG. 4, in the present embodiment, the sound wave 12 incident from the sound wave generator 13 uses a sound wave having directivity.

  In the present embodiment, by using sound waves having directivity, signal disturbance due to irregular reflection of sound waves in the measurement object 11 can be prevented.

[Fifth Embodiment]
A strain measuring apparatus according to a fifth embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a conceptual diagram showing a strain measuring apparatus according to the fifth embodiment. In addition, the same code | symbol is attached | subjected about the same member as the measuring apparatus 10 of 1st thru | or 4th embodiment, and the description is abbreviate | omitted.
As shown in FIG. 5, in the present embodiment, a filter 22 that takes into account the change in wavelength of the Doppler shift due to the speed of sound is used for the received signal of the reflected electromagnetic wave 16.

Although electromagnetic waves are reflected by sound waves, the reflected sound waves are moving in the same direction as the traveling direction of the electromagnetic waves, and thus have an influence of Doppler shift. Therefore, the reflected electromagnetic wave 16 of the electromagnetic wave is longer than the incident wavelength.
In the present embodiment, since the filter 22 is arranged between the sound wave receiver 17 and the signal processing device 19, the band of the received signal is limited, and the object to be measured of the incident electromagnetic waves is thereby limited. The influence of irregular reflection due to the boundary of 11 or the like is removed.

[Sixth Embodiment]
A strain measuring apparatus according to a sixth embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a conceptual diagram showing a strain measuring apparatus according to the sixth embodiment.
As shown in FIG. 7, in the present embodiment, the surface of the object to be measured 11 is covered with the metal foil 51, and a thin wire 52 is embedded in the object to be measured 11 in advance. .
As a result, the directivity of the electromagnetic wave from the high frequency lead wire 33 is improved.
It is preferable that the fine wire 52 be several tens of μm or less, particularly preferably several μm, because the influence of unevenness due to embedding does not occur.

  Further, as shown in FIG. 8, instead of not covering the metal foil 51, the conductive wires may be two parallel lines 52-1 and 52-2 to stabilize the propagation intensity change.

[Seventh Embodiment]
A seventh embodiment according to the present invention will be described with reference to the drawings.
FIG. 9 is a conceptual diagram in which the strain measuring device of the present invention is used for wind turbine distortion.
As shown in FIG. 9, the strain measuring device 10 is installed on the rib 61 in the internal space of the windmill 60 to measure the deformation of the blade 62 of the windmill 60. A signal from the strain measuring device 10 is sent to the signal processing device 19 through a lead wire 63, and a change in structure is measured here.

  As a result, since no sensor is provided on the surface of the blade 62 as in the prior art, air resistance does not become a problem. Therefore, for example, the distortion of the blades of the windmill is constantly measured, and when there is an influence of a gust of wind, for example, the operation control of the windmill can be performed quickly.

In addition, when measuring an internal defect of an object to be measured, since the sensor is not embedded, the measurement range can be expanded.
In addition, the strain measuring device according to the present invention can be applied not only to measuring the strain of the blades of a windmill but also to measuring the strain of a concrete structure and the deformation of a composite material such as FRP.

  Hereinafter, specific measurement of the measurement apparatus of the present invention will be described in detail together with examples.

First, a material strain measurement procedure will be described.
As shown in FIG. 3, the measuring device used in this example has the sound wave generating device 13 and the electromagnetic wave generating device 15 coaxial with the object to be measured 11, and the pulsed sound wave 12 is incident thereon. Further, GFRP (glass fiber reinforced plastic) was used as the material of the object 11 to be measured, for example. Here, for example, when the sound velocity Vac0 of a material without distortion (GFRP) is 3200 m / s and the strain generation range is 0 to 1%, the relationship between the sound velocity and the strain follows the following formula (1), and the range of Vac Is expected to be 3200 m / s to 3216 m / s.
Vac = Vac0 / √ (1-ε) (1)

  If the frequency of the electromagnetic wave is 32 GHz and the wavelength in the electromagnetic wave material is λr = 6.25 mm, the wavelength λac of the sound wave is 3.125 mm from the reflection condition of the electromagnetic wave, and the frequency is 1024 kHz to 1029 kHz is expected.

Next, as shown in FIG. 10, consider the case of measuring a material in which 1% strain is generated in the region of distances L1 and L2.
In the region of the object 11 to be measured, an electromagnetic wave is continuously input, and a pulsed sound wave of, for example, t = 0.1 msec (pulse length 320 mm) is incident while changing the frequency in consideration of spatial resolution.

When the velocity of the electromagnetic wave in the object to be measured is Vr, the return time of the incident electromagnetic wave can be converted into a distance from the following equation (2).
t = L / Vac + L / Vr (2)
Here, for example, when t = 1.5 × 10 ⁻³ (sec), Vac = 3200 (m / sec), and Vr = 2.0 × 10 ⁸ (m / sec), the reflected wave is L = 4. Returned from the position of less than .8mm (4.7999232mm).

  FIG. 11 shows the relationship when the return time of the reflected electromagnetic wave and the signal intensity are measured while changing the frequency of the sound wave in a three-dimensional graph. In FIG. 11, the horizontal axis (X axis) is the return time, the vertical axis (Y axis) is the signal intensity, and the axis in the depth direction (Z axis) is the sound wave frequency.

As shown in FIG. 11, even when the signal does not return, a low signal (small waveform) like noise is measured. In FIG. 11, this is indicated by a solid thin line. The intensity is expected to change slightly depending on the state of the material, but it can be clearly distinguished whether there is reflection or not.
In FIG. 11, the portion with reflection is indicated by a thick line. A dotted line is for making the correlation of each axis easy to understand. For example, the horizontal dotted line indicates the frequency of f1 and f2, and the depth direction (Z direction) dotted line indicates that the region where the signal changes at the frequencies f1 and f2 corresponds to the times t1 and t2. It shows that.

The measurement will be described below. FIG. 16 shows a processing flow at the time of measurement.
1) First, when measurement is started, the frequency fac of sound waves is repeated at f0 to f3 (S1). This sets the frequency fac and outputs a sound wave (S1-1). Next, an electromagnetic wave pulse is output (S1-2). This is repeated from the emission of electromagnetic waves to the end of the material (S1-3). During this repetition, the reflected electromagnetic wave is received as a function of time (S1-3-1).
2) The reflected wave signal is converted from time to distance (S-2).
3) The center wavelength C (L) of the reflected wave is obtained from the spectrum R (fac) of the reflected wave at each position (S-3).
4) The strain at each position is calculated from the relationship between the center wavelength and strain obtained in advance (S-4).

Specifically, it is performed as follows.
Here, when the material is not deformed, since the frequency of the sound wave is not changed, it can be confirmed that the reflected signal returns as shown by the thick solid line at the frequency f1 in FIG.
On the other hand, in a section where distortion occurs, a reflected signal cannot be confirmed at f1 as shown by a solid thin line.

  Next, when the frequency is gradually increased, it can be confirmed that the reflected signal returns between the times t1 and t2 at the frequency f2.

  As described above, the strain distribution in the measurement region of the target material can be calculated from the relationship between the signal intensity corresponding to the distance and the frequency (the presence or absence of the signal) using the above formula.

FIG. 12 shows a cross section perpendicular to the time axis at the times ta and tb in FIG. The cross-sectional views at the respective times are shown in FIG. 13 for ta and in FIG. 14 for tb.
In FIGS. 13 and 14, the horizontal axis represents frequency, and the vertical axis represents received intensity. As shown in these drawings, the spectrum is shaped on the time axis at the positions of time ta and tb.
This function is R (L, fac) as the frequency characteristic of the intensity distribution of the reflected wave at the distance L (converted from time t).

Here, the center frequency C (L) is determined from the spectrum (here, the maximum value is used. That is, R (L, C (L)) is the maximum value of the spectrum of the distance L).
Next, let this center frequency be C (L) as the center frequency of the reflected wave at the distance L. For example, the position of the time ta is La, and the center frequency is C (La).
Finally, the center frequency at each position is converted into distortion.
For this conversion, as shown in FIG. 15, the relationship between “the frequency of the sound wave and the strain of the material that reflects the radio wave at the frequency”, which has been separately obtained in advance, is used. For example, the strain at the distance La rises vertically at the frequency of C (La) (dotted line), and the horizontal (dotted line) strain value ε (La) corresponds to the intersection of the lines indicating the above relationship (thick line in the figure). .
By repeating the above-described procedure, the strain distribution at each position is obtained from the relationship shown in FIG.

  As described above, the strain measuring apparatus according to the present invention can continuously measure the strain without affecting the surface of the object to be measured, and particularly measures the strain of the internal structure without destroying the structure. Suitable for use.

It is the schematic of the distortion | strain measuring apparatus concerning 1st Embodiment. It is the schematic of the distortion | strain measuring apparatus concerning 2nd Embodiment. It is the schematic of the distortion measuring device concerning 3rd Embodiment. It is the schematic of the distortion | strain measuring apparatus concerning 4th Embodiment. It is the schematic of the distortion | strain measuring apparatus concerning 5th Embodiment. It is a figure which shows the state which connects the vibrator | oscillator and lead wire of a distortion measuring device to a to-be-measured object. It is the schematic of the distortion | strain measuring apparatus concerning 6th Embodiment. It is the schematic of the other distortion | strain measuring apparatus concerning 6th Embodiment. It is the schematic which shows the state which installed the strain measuring device in the windmill. It is explanatory drawing of the to-be-measured object of an Example. It is a related figure of the return time of an Example, receiving intensity, and the frequency of a sound wave. It is a related figure of the return time of an Example, receiving intensity, and the frequency of a sound wave. It is a relationship figure of the frequency (f1) and reception intensity of an Example. It is a relationship figure of the frequency (f2) of an Example, and receiving intensity. It is a related figure of the center frequency and distortion of an Example. It is a processing flow figure of an Example. It is the schematic of the distortion measurement of the conventional windmill.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Strain measuring device 11 Object to be measured 12 Sound wave 13 Sound wave generating device 14 Electromagnetic wave 15 Electromagnetic wave generating device 16 Reflected electromagnetic wave 17 Electromagnetic wave receiver 18 Signal 19 Signal processing device 20 Time measuring device 21 Timing device 22 Filter

Claims (9)

A sound wave generator for injecting sound waves into the measurement object;
An electromagnetic wave generator for injecting an electromagnetic wave into a measurement object;
A receiver for receiving reflected electromagnetic waves;
A strain measurement apparatus comprising: a signal processing apparatus that processes a received signal. In claim 1,
A strain measuring apparatus characterized by changing the frequency of an incident sound wave. In claim 1 or 2,
A strain measuring apparatus, wherein an electromagnetic wave is incident on an object to be measured through a high-frequency lead wire, and a thin lead wire connected to the high-frequency lead wire is embedded in the object to be measured. In claim 3,
A strain measuring apparatus characterized by covering an object with a metal foil. In claim 3,
A strain measuring device, wherein the two thin conductive wires are embedded in parallel. In any one of Claims 1 thru | or 5,
A strain measuring apparatus for a rotating body, wherein the object to be measured is a rotating body supported rotatably with respect to a fixed side. In claim 6,
The rotating body strain measuring device, wherein the rotating body is a blade of a wind turbine for wind power generation. A sound wave and an electromagnetic wave are incident on an object to be measured,
A strain measurement method characterized by receiving a reflected electromagnetic wave and measuring strain by a received signal. In claim 8,
A strain measurement method for receiving reflected electromagnetic waves while changing the frequency of incident sound waves.

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