KR100217871B1 - Fiber-optic interferometers used in a system for detecting the strain of structures and method for measuring the strain of structures using the same - Google Patents

Abstract

The present invention provides a reference for inputting the light beam of the original wavelength from the laser light source 16 to the structure in order to inexpensively and simply measure the amount of deformation of the structure and to detect the direction of deformation such as tensile deformation or compression deformation. Leg 11, a sensing leg 12 that extends from the structure to the first photodetector 17 and outputs a sensing signal, and one side prevents light from being reflected at the end of the optical fiber, and the other side has a second photodetector ( 18) to provide an optical fiber interference measuring device which comprises a comparison leg 13 for outputting a comparison signal for detecting the type of deformation, the optical fiber interference measuring device being a Michelson type 3 × 3 optical fiber interference measuring device. (10) or a double Fabry comprising first and second Fabry-Perot optical fiber interference meters (20a, 20b) after the light from the laser light source (26) is split by the optical fiber linkage (27a). In the method for detecting deformation using a strain detection system including the optical fiber interference measuring device (10, 20), the detection signal acquisition step, the comparison signal acquisition step, A cross discrimination step and a cross-sequence inspection step for determining whether the detection signal S1 and the comparison signal S2 intersect with the appropriately set reference line R, and the order thereof, The amount of deformation is measured using the sine wave coefficient step of increasing or decreasing the number and the number of counted sine waves.

Description

Fiber-optic interference measuring instrument used in system for detecting deformation of structure and method of detecting deformation of structure using such system

The invention relates to interferometric optical fiber sensors, i.e. fiber-optic interferometers and such deformations, which are used in strain detection systems which measure the amount of deformation of a structure as well as detect the direction of deformation. The present invention relates to a deformation detection method using a detection system, and more particularly, to an optical fiber interference measuring device and a deformation detection method using the same, which eliminate errors of measurement values caused by external factors such as temperature, vibration, or pressure, and obtain accurate measurements. It is about.

The optical fiber interferometer is, for example, a Mach-Zehnder type interferometer, a Michelson type interferometer or a Fabry-Perot type interferometer. There are several kinds.

For such optical fiber interference meters, the invention is named Fiber optic strain sensor and read-out system and was issued to Martin Marietta Corporation on December 19, 1995. The specification of U.S. Patent No. 5,477,323, filed by the inventors of the present invention and filed with this application by the applicant of the present application, is a system and method for measuring the amount of deformation of a structure using an interference light beam. It is described in detail in the specification.

Such interfering optical sensors can be used well to measure the amount of deformation of a structure, as described in the specification of the application mentioned above, but are sensitive to environmental factors such as temperature changes, pressure changes or vibrations as well as deformation of the structure. Therefore, it is important to remove noise due to environmental factors from the output signal of the coherent optical sensor and to extract only the value due to the deformation amount of the structure.

However, the specification of the above-mentioned application refers only to measuring the amount of deformation of the structure using interfering optical sensors, and does not mention whether such deformation is shrinkage or stretch deformation.

Joseph A. Joseph A. McClintock and Jeffrey P. Bethesda, Maryland, USA, invented by Jeffrey P. Andrews, filed November 6, 1992, and named Fabry-Perot readout technique using wavelength tuning. In US Patent Application No. 927,397 of Martin Marietta Corporation of Materials, a method of determining the type of deformation as well as the type of deformation, that is, whether it is shrinkage or stretch deformation, using an interfering optical sensor is proposed. It is becoming.

However, in US Patent Application No. 927,397, the amount and type of deformation are obtained from two signals tuned to the output signal of the interference type optical sensor and the original wavelength of the light source. That is, not only can not solve the problem caused by the mixing of error factors due to environmental factors such as temperature change, pressure change or vibration, but also requires an electrically operated tuning device for tuning the original wavelength of the light source. It's very complicated.

The present invention overcomes the problems in the method and system for measuring the amount of deformation of the structure, and determining the type and direction of the structure using the conventional optical fiber interference measuring apparatus as described above, and minimizes the measurement error in an inexpensive and simple way to obtain accurate measurement results. To get it.

1 is a block diagram schematically showing the configuration of an optical fiber interference measuring instrument used in the deformation detection system of a structure according to the first embodiment of the present invention,

2 is a block diagram schematically showing the configuration of an optical fiber interference measuring instrument used in the deformation detection system of a structure according to a second embodiment of the present invention.

3 is an external perspective view showing the form in which the optical fiber interference measuring instrument shown in FIG.

4 is a waveform diagram illustrating a method of detecting a type of deformation of a structure by an output signal of the optical fiber interference measuring instruments shown in FIGS. 1 and 2;

5 and 6 are graphs showing actual signal processing results by the optical fiber interference measuring devices shown in FIG. 1 and FIG.

* Explanation of symbols for main parts of the drawings

10: Michelson type 3 × 3 optical fiber interference measuring instrument 11, 22: reference leg

12, 23a: detection leg 13, 23b: comparison leg

15, 27a, 27b, 27c: fiber optic linker 16, 26: laser light source

17, 29a: first photodetector 18, 29b: second photodetector

20: Dual Fabry-Perot Fiber Optic Interferometry

20a, 20b: Fabry-Perot type fiber optic interference measuring instrument

R: reference line S1: detection signal

S2: comparison signal IML: glycerin

According to this method for solving the above problems, in the optical fiber interference measuring apparatus used in the deformation detection system for measuring the amount of deformation of the structure and the direction of deformation, the light beam of the original wavelength from the laser light source is A reference leg inputted to the detection leg, a detection leg that extends from the structure to the first photodetector, and outputs a detection signal, and one side prevents light from being reflected at the end of the optical fiber, and the other side leads to the second photodetector. There is provided an optical fiber interference measuring device including a comparison leg for outputting a comparison signal for detecting a kind.

According to the present invention, the optical fiber interference measuring device may be a Michelson type 3 × 3 optical fiber interference measuring device.

According to the present invention, the optical fiber interference measuring device may be a dual Fabry-Perot type optical fiber interference measuring device including first and second Fabry-Perot type optical fiber interference measuring devices.

In addition, according to the present invention, in the deformation detection method for measuring the amount of deformation of the structure and also detects the type of deformation, the detection to obtain a detection signal from the first photodetector while injecting a light beam from the laser light source through the reference leg A signal acquisition step, a comparison signal acquisition step of obtaining a comparison signal having the same wavelength as the incident light beam in the second photodetector, setting a reference line on an appropriate wave height in consideration of the amplitude of the detection signal and the comparison signal, A cross discrimination step of determining whether the comparison signals intersect the reference line, a cross order checking step of checking an order in which the detection signal and the comparison signal intersect the reference line, and the detection without altering the order of intersection When the signal crosses the sensing line, the number of sinusoids (m) is increased by 1, and the crossing order is changed to When the ground signal intersects the sensing line, the amount of deformation of the structure is determined by the following Equation 1 using the sine wave coefficient step of decreasing the number of sine waves by 1 and the number of counted sine waves (m). Provided is a method for detecting deformation of a structure, characterized in that the measurement.

은 구조물의 변형률이고, L은 광섬유의 게이지길이이며, C는 게이지 상수임.From here,

Where is the strain of the structure, L is the gauge length of the fiber, and C is the gauge constant.

In addition, according to the present invention, each time the detection signal crosses the reference line may further include a reference line resetting step of resetting the position of the reference line.

EXAMPLE

Now, with reference to the accompanying drawings will be described in detail the preferred embodiments of the optical fiber interference measuring apparatus used in the deformation detection system of the structure according to the present invention and the deformation detection method of the structure using the deformation detection system of such a structure.

[First Embodiment]

1 schematically shows a Michelson-type optical fiber interference measuring instrument used in the deformation detection system of a structure according to the first embodiment of the present invention. The optical fiber interference measuring instrument 10 shown in FIG. 1 is composed of three legs, unlike a conventional microson-type optical fiber interference measuring instrument, and the first leg includes a light beam having an original wavelength from the laser light source 16. The reference leg 11 is input to the inside of the structure 19 via the optical fiber linker 15, and the second leg is connected to the first photodetector 17 through the optical fiber linker 15 from the inside of the structure and detects the detection signal. It is a detection leg 12 for outputting, and the third leg is a line that does not need one side is buried with glycerin so that the light is not reflected back from the end of the optical fiber and the other side leads to the second photodetector 18 and deformed. A comparison leg 13 for outputting a comparison signal for detecting the type of. Here, such an optical fiber interference measuring device 10 will be referred to as a Michelson type 3x3 optical fiber interference measuring device.

3 광섬유간섭측정기(10)를 이용하여 구조물의 변형의 종류 및 방향을 탐지하고 양을 측정하는 방법에 대해 설명하겠따.Now, the Michelson equation 3 according to this embodiment

3 How to detect the type and direction of deformation of the structure using the optical fiber interference measuring instrument (10) and how to measure the amount.

3 광섬유간섭측정기(10)의 기준레그(11)를 통해 레이저광원(16)으로부터 광빔을 입사시키면, 제1광검출기(17)에서는 제4도의 실선으로 도시한 것과 같은 감지신호(S1)를 얻게 되며, 제2광검출기(18)에서는 제4도의 점선으로 도시한 것과 같은 비교신호(S2)를 얻게 된다. 이러한 두 개의 신호(S1, S2)의 진폭을 고려하여 적절한 파고상에 기준선을 설정하고, 그 신호(S1, S2)들이 상기 기준선(R)과 교차하는지의 여부를 판별한다. 상기 감지신호(S1)와 상기 비교신호(S2)가 상기 기준선(R)과 교차하는 순서, 즉, 상기 감지신호(S)와 상기 비교신호(S2) 중에서 어느 것이 기준선(R)과 먼저 교차하는지를 검사한다. 교차순서가 바뀌지 않은 채로 상기 감지신호(S1)가 상기 감지선(R)과 교차하는 경우에는 정현파의 개수 m을 1만큼 증가시키고, 교차순서가 바뀌면서 상기 감지신호(S2)가 상기 감지선(R)과 교차하는 경우에는 정현파의 개수 m을 1만큼 감소시킨다. 상기 감지신호(S1)가 상기 기준선(R)과 교차하지 않으면, 정현파의 개수 m은 변하지 않는다. 위와 같이 구해진 정현파의 개수 m을 이용하여 다음의 수학식 1에 의해 구조물의 변형의 양을 측정한다.Michelson equation 3 according to this embodiment

3 When the light beam is incident from the laser light source 16 through the reference leg 11 of the optical fiber interference measuring device 10, the first light detector 17 obtains a detection signal S1 as shown by the solid line in FIG. In the second photodetector 18, a comparison signal S2 as shown by a dotted line in FIG. 4 is obtained. In consideration of the amplitude of these two signals S1 and S2, a reference line is set on an appropriate wave height, and it is determined whether the signals S1 and S2 cross the reference line R. The order in which the detection signal S1 and the comparison signal S2 intersect the reference line R, that is, which of the detection signals S and the comparison signal S2 intersects the reference line R first. Check it. When the detection signal S1 crosses the detection line R without changing the crossing order, the number m of sine waves is increased by 1, and the detection signal S2 is detected by the detection line R while the crossing order is changed. ), The number of sinusoids m is reduced by one. If the detection signal S1 does not cross the reference line R, the number m of the sine wave does not change. Using the number m of sinusoids obtained as described above, the amount of deformation of the structure is measured by Equation 1 below.

[Equation 1]

은 구조물의 변형률이고, L은 광섬유의 게이지길이이며, C는 게이지상수임.From here,

Is the strain of the structure, L is the gauge length of the fiber, and C is the gauge constant.

In addition, in the above process, the cross order of the detection signal S1 and the comparison signal S2 has been changed in the order of crossing, indicating that the type of deformation of the structure is changed from shrinkage strain to stretch strain or stretch strain to shrinkage strain. it means.

More preferably, whenever the detection signal S1 crosses the reference line R, the position of the reference line R may be reset.

Even after the above process is completed, if the light beam continues to be incident from the laser light source 16 through the reference leg 11 of the Michelson type 3 × 3 optical fiber interference measuring instrument 10 and the acquisition of data continues, the above process Repeat to run.

Second Embodiment

FIG. 2 schematically shows a Fabry-Perot type optical fiber interference measuring instrument used in the deformation detection system of the structure according to the first embodiment of the present invention. The optical fiber interference measuring device 20 shown in FIG. 2 is a dual Fabry-Perot type optical fiber interference measuring device including two conventional Fabry-Perot optical fiber interference measuring devices 20a and 20b. The transducers 2a of the first Fabry-Perot optical fiber interference measuring device 20a and the transducers 21b of the second Fabry-Perot optical fiber interference measuring device 20b are arranged side by side with a predetermined interval, and the first Fabry-Peh The reference leg 22a of the lot type fiber interference meter 20a and the reference leg 22b of the second fabric-ferret type fiber interference meter 20b are connected by an optical fiber linker 27a, and the first fabric-ferret type Light is incident on the reference leg 22a of the optical fiber interference measuring instrument 20a and the reference leg 22b of the second Fabry-Perot type optical fiber interference measuring instrument 20b, and the unused optical fiber of the rear end of the optical fiber linkers 27b and 27c is used. Glycerin is applied at the end to prevent the light beam from reflecting. Since the transducers 21a and 21b of the first and second Fabry-Perot optical fiber interference measuring instruments 20a and 20b have constant air gaps 28a and 28b, the strain which is given from the outside according to the deformation of the structure is the air gap. As the lengths of the 28a and 28b change, the output signals output through the legs acting as the sensing leg 23a and the comparative leg 23b are sinusoidal waveforms as shown in FIG. If the lengths of the air gaps of the transducers 21a and 21b are slightly different, there is a phase difference as shown in FIG. 4 between the output signals detected by the respective photodetectors 29a and 29b. However, as shown in FIG. 3, the glass tube of the transducer 21a of the first Fabry-Perot type optical fiber interference measuring instrument 20a and the glass tube of the transducer 21b of the second Fabry-Perot type optical fiber interference measuring instrument 20b. By side-by-side fixed by sliding movement impossible to keep the phase shift amount of the two output signals to maintain a signal as shown in FIG.

Now, a method of detecting and measuring the type of deformation of a structure by using the dual Fabry-Perot optical fiber interference measuring device 20 according to this embodiment will be described.

When the light beam is incident from the laser light source 26 through the reference leg 22a of the dual Fabry-Perot type fiber interference measuring instrument 20 according to this embodiment, the first photodetector 29a is shown by the solid line of FIG. The detection signal S1 is obtained, and the second photodetector 29b obtains the comparison signal S2 as shown by the dotted line in FIG. 4. In consideration of the amplitude of these two signals S1 and S2, a reference line is set on an appropriate wave height, and it is determined whether the signals S1 and S2 cross the reference line R. The order in which the detection signal S1 and the comparison signal S2 intersect the reference line R, that is, which of the detection signals S and the comparison signal S2 intersects the reference line R first. Check it. When the detection signal S1 crosses the detection line R without changing the crossing order, the number m of sine waves is increased by 1, and the detection signal S2 is detected by the detection line R while the crossing order is changed. ), The number of sinusoids m is reduced by one. If the detection signal S1 does not cross the reference line R, the number m of the sine wave does not change. Using the number m of sinusoids obtained as described above, the amount of deformation of the structure is measured by Equation 1 below.

[Equation 1]

은 구조물의 변형률이고, L은 광섬유의 게이지길이이며, C는 게이지상수임.From here,

Is the strain of the structure, L is the gauge length of the fiber, and C is the gauge constant.

In addition, in the above process, the crossing order of the detection signal S1 and the comparison signal S2 has been changed in order that the type of deformation of the structure is changed from shrinkage strain to stretch strain or stretch strain to shrinkage strain. it means.

More preferably, whenever the detection signal S1 crosses the reference line R, the position of the reference line R may be reset.

Even after the above process is completed, if the light beam continues to be incident from the laser light source 26 through the reference leg 21a of the dual Fabry-Perot optical fiber interference measuring device 20 and the acquisition of data continues, the above process is continued. Do it repeatedly.

5 and 6 show the optical fiber interference measuring devices 10 and 20 in order to show the effectiveness of an algorithm for digitally processing the output signals of the optical fiber interference measuring devices 10 and 20 according to the first and second embodiments. Are graphs showing actual signal processing results. It can be seen that the detection signal S1 and the comparison signal S2 have a constant phase difference. Therefore, the graph PS of the phase difference in FIGS. 5 and 6 can be obtained by processing the data of the sensing signal S1. When the type of deformation is changed in FIGS. 5 and 6, it is understood that the order in which the reference signal S1 and the comparison signal S2 intersect the reference line is reversed. In addition, it can be seen that when the values of the graphs PS of the phase differences of FIGS. 5 and 6 are substituted into Equation 1, the strain becomes as it is.

The embodiments of the present invention described above are intended to illustrate but not limit the invention.

Therefore, the present invention is not limited to the embodiments described above, but will also include all changes, modifications or adjustments that can be made by those skilled in the art without departing from the spirit and technical spirit of the invention, and the appended patents The claims are intended to cover all such.

In the present invention as described above, the deformation detection system of the structure using the optical fiber interference measuring instrument and the deformation detection method of the structure using the deformation detection system of such a structure are cheap and simple to obtain the type, direction, and quantity of the deformation, as well as measurement errors. Minimize the to obtain accurate measurement results.

Claims (5)

In the optical fiber interference measuring apparatus used in the deformation detection system for detecting the direction of deformation as well as measuring the amount of deformation of the structure, a reference leg that receives the light beam of the original wavelength from the laser light source, and the first light from the structure A detection leg that leads to the detector and outputs a detection signal, and one side that prevents light from being reflected at the end of the optical fiber and the other to a second photo detector, which outputs a comparison signal for detecting the type of deformation. Optical fiber interference measuring device comprising a. The optical fiber interference measuring device according to claim 1, wherein the optical fiber interference measuring device is a Michelson-type 3x3 optical fiber interference measuring device (10), and a light beam having an original wavelength from the laser light source (16) is passed through the optical fiber linking device (15). A reference leg 11 input to the detection leg, and a detection leg 12 for outputting a detection signal from the inside of the structure through the optical fiber linker 15 to the first photodetector 17 and one end of the optical fiber. The optical fiber interference characterized in that it comprises a comparison leg (13) for burying the glycerin so that the light is not reflected back and the other side is led to the second photodetector (18) and outputs a comparison signal for detecting the type of deformation. Measuring instrument. The optical fiber interference measuring device according to claim 1, wherein the optical fiber interference measuring device is a double Fabry-Perot optical fiber interference measuring device (20) including first and second Fabry-Perot optical fiber interference measuring devices (20a, 20b), and the first Fabry- The transducers 21a of the ferot-type optical fiber interference measuring device 20a and the transducers 21b of the second Fabry-Perot optical fiber interference measuring device 20b are arranged side by side with a predetermined interval, and the first Fabry-Perot optical fiber interference The comparison leg 22b of the reference leg 22a of the measuring device 20a and the second Fabry-Perot type optical fiber interference measuring device 20b are connected by the optical fiber linkers 27a, 27b, and 27c. The lengths S1 and S2 of the air gaps of the transducers 21a and 21b of the Fabry-Perot type optical fiber interference measuring instruments 20a and 20b of 2 are different, and the transducers of the first Fabry-Perot type optical fiber interference measuring instrument 20a are different. One of the glass tube of the probe 21b of the glass tube of 21a and the second Fabry-Perot type optical fiber interference measuring instrument 20b. The optical fiber interference measuring device, characterized in that the side is fixed to the sliding movement impossible and the other side is free. In the deformation detection method of measuring the amount of deformation of the structure and detecting the type of deformation, the first light detector 17 detects the light beam while injecting the light beam from the laser light sources 16 and 26 through the reference leg 11. A detection signal acquisition step of obtaining a signal S1, a comparison signal acquisition step of obtaining a comparison signal S2 having the same wavelength as the incident light beam in the second photodetector 18, the detection signal S1 and the comparison signal ( A cross discrimination step of setting a reference line on an appropriate wave height in consideration of the amplitude of S2) and determining whether the detection signal S1 and the comparison signal S2 cross the reference line R, and the detection signal. (S1) and the cross-sequence check step of checking the order in which the comparison signal (S2) intersects the reference line (R), and the detection signal (S1) crosses the detection line (R) without changing the crossing order. The number of sinusoids (m) is increased by one, When the detection signal S2 crosses the detection line R while the order is changed, a sine wave coefficient step of reducing the number of sine waves m by 1 and the number of sine waves counted by Deformation detection method of the structure, characterized in that for measuring the amount of deformation of the structure by the equation (1).

From here,

Is the strain of the structure, L is the gauge length of the fiber, and C is the gauge constant. The deformation detection method according to claim 4, further comprising a reference line reset step of resetting the position of the reference line (R) whenever the detection signal (S1) intersects the reference line (R).

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