CN103940359A - Fiber grating differential strain gauge and manufacturing and using method thereof - Google Patents

Abstract

The invention provides a fiber grating differential strain gauge. The fiber grating differential strain gauge comprises a first fiber grating, a second fiber grating, an elastomer and installation arms, wherein the elastomer is a deformable body which is hollow and is in axial symmetry and central symmetry, the two ends of the first fiber grating are bonded to one side of the elastomer, the two ends of the second fiber grating are bonded to the other side of the elastomer, the first fiber grating and the second fiber grating are perpendicular to each other, grating bodies of the fiber gratings penetrate through the center of the elastomer and do not make contact with each other, the installation arms are fixed to the two sides of the elastomer, the installation arms and the first fiber grating are arranged in the same direction, the thickness of each installation arm is larger than that of the elastomer, and open grooves which penetrate through a tail fiber of the first fiber grating are formed in the installation arms. According to the fiber grating differential strain gauge, the two-end bonding mode is adopted for the structure, it is ensured that stress of grating parts is uniform, the chirp phenomenon is eliminated, detection accuracy is ensured, a manufacturing process of the fiber grating differential strain gauge can be simpler through the two-end bonding mode, and operation is easier.

Description

A kind of fiber grating differential strain sheet and making and use method thereof

Technical field

The invention belongs to Fibre Optical Sensor parts, be specifically related to a kind of fiber grating differential strain sheet and making and use method thereof.

Background technology

In order to carry out the force analysis of structure or the member that monitoring is subject to mechanical load, often use resistance strain gage to detect the strain of the structural detail of the power that is loaded.This resistance strain gage is comprised of substrate, sensitive grid, overlayer and extension line, and sensitive grid is the responsive part that resistance-strain amount is converted into resistance change; Substrate and overlayer have the effect of location and protective resistance silk and measured body insulation; Lead-in wire plays a part to connect measure traverse line; In order to detect the strain relevant to load, these resistance strain gages are laid on monitored member, and by transformation for strain, are electric signal by measuring the resistance variations of sensitive grid, and this signal and strain or acting force are proportional.Resistance strain gage have volume little, be easy to the features such as installation, but it is very responsive for the impact of electromagnetic field or high-voltage field, and does not allow to use in inflammable and explosive occasion.

Optical fiber sensing technology is to follow Fibre Optical Communication Technology and an important invention producing, due to this technology employing is the mode of optical signal modulation, therefore possesses in essence good anti-electromagnetic interference capability, while is along with further investigation and the improvement of manufacture craft, make it possess the features such as wide dynamic monitoring scope, high sensitivity, optical signal transmission distance, be convenient to networking and realize distributed measurement, these advantages are engineering monitoring effective solution are provided, and have therefore been subject to domestic and international researchist's extensive concern.But, in the engineering application of fiber-optic grating sensor, also exist following problem: (1), because fiber-optic grating sensor is all responsive to temperature and strain, need solve the problem of temperature and strain cross sensitivity during application.(2) fiber grating itself has certain length, if be directly fixed on monitored member, is difficult to guarantee that the suffered strain field of grating is uniformly, so just easily causes the warbling of fiber grating, the precision that impact is measured.(3) directly fiber grating is solidified on monitored body, be not easy to through engineering approaches construction.

Summary of the invention

The present invention is intended to overcome the above-mentioned problem of fiber grating sensing technology, and a kind of FBG strain gauge of simple in structure, packaging technology easy operating is provided.

The present invention solves the problems of the technologies described above taked technical scheme to be: a kind of fiber grating differential strain sheet, it is characterized in that: it comprises the first fiber grating, the second fiber grating, elastic body and hold-down arm, elastic body be a hollow, not only rotational symmetry but also centrosymmetric deformable body; Wherein the two ends of the first fiber grating stick on elastomeric one side, and the two ends of the second fiber grating stick on elastomeric another side, and the first fiber grating is mutually vertical with the second fiber grating, and the grating of the two is all by elastomeric center and do not contact; Described hold-down arm is fixed on elastomeric both sides, and with the first fiber grating in same direction; The thickness of hold-down arm is greater than elastomeric thickness, and hold-down arm is provided with the fluting for the tail optical fiber through the first fiber grating.

Press such scheme, first, second fiber grating and elastomeric affixed points are respectively equipped with fluting.

Press such scheme, described elastic body is circular deformable body or hollow regular polygon deformable body.

A method for making for above-mentioned fiber grating differential strain sheet, is characterized in that:

On elastomeric two sides, one cross-notching is set respectively, the line of every cross-notching is all by elastomeric center;

Hold-down arm is fixed on elastomeric both sides, and hold-down arm also arranges fluting, the fluting of hold-down arm and elastomeric wherein a pair of being recessed on same straight line;

Through the first fiber grating of prestretched, along the fluting of elastic body one side, place, the fluting gluing that its grating is arranged on elastomeric central shaft and its tail optical fiber is placed on elastic body and hold-down arm is fixed; Through the second fiber grating of prestretched, along the fluting of elastic body another side, place, its grating is arranged on elastomeric central shaft and its tail optical fiber is placed on elastomeric fluting gluing and fixes.

Utilize the using method of the fiber grating differential strain sheet of above-mentioned method for making making to be:

Fiber grating differential strain sheet is fixed on monitored body by hold-down arm, monitored body strain changes the deformation that causes Shape-changeable ring, and then make the first fiber grating and the second fiber bragg grating center wavelength is poor changes, by detecting two variable quantities that fiber bragg grating center wavelength is poor, draw the dependent variable that monitored body produces.

Beneficial effect of the present invention is:

1, utilize FBG strain gauge and the method for making of structure of the present invention, the difference that makes two grating wavelength variable quantities only with the stressed big or small linear dependence of foil gauge, and temperature independent, eliminated the cross sensitivity of strain and temperature; The mode that structure of the present invention adopts two ends to paste, can guarantee that grating position is stressed evenly, warbling of elimination phenomenon, thereby guaranteed the precision detecting, the mode that paste at two ends also can make the manufacture craft of foil gauge simpler, be easier to operation, this provides strong support by the promotion and application for fiber grating sensing technology; Hold-down arm is slightly thicker than elastic body, to guarantee that foil gauge only passes through the stressed of the monitored body of hold-down arm perception, thereby drives elastic body to produce deformation, and in the time of can eliminating the monitored body of the direct contact of foil gauge, unbalance stress affects accuracy and the consistance of foil gauge.

2, first, second fiber grating must be pasted on elastic body after prestretched, can make like this elastic body align negative strain and all can realize perception.

Accompanying drawing explanation

Fig. 1 is the structural representation of one embodiment of the invention.

Fig. 2 is the vertical view of Fig. 1.

Fig. 3 is the structural representation of another embodiment of the present invention.

Fig. 4 is the vertical view of Fig. 3.

In figure: 1-the first fiber grating, 2-the second fiber grating, 3-ring-type deformable body, 4-the first hold-down arm, 5-the second hold-down arm

Embodiment

Below in conjunction with instantiation and accompanying drawing, the present invention will be further described.

A fiber grating differential strain sheet, is characterized in that: it comprises the first fiber grating, the second fiber grating, elastic body and hold-down arm, elastic body be a hollow, not only rotational symmetry but also centrosymmetric deformable body; Wherein the two ends of the first fiber grating stick on elastomeric one side, and the two ends of the second fiber grating stick on elastomeric another side, and the first fiber grating is mutually vertical with the second fiber grating, and the grating of the two is all by elastomeric center and do not contact; Described hold-down arm is fixed on elastomeric both sides, and with the first fiber grating in same direction; The thickness of hold-down arm is greater than elastomeric thickness, and hold-down arm is provided with the fluting for the tail optical fiber through the first fiber grating.

Embodiment mono-:

Fig. 1 is the structural representation of the embodiment of the present invention one, Fig. 2 is the vertical view of Fig. 1, it comprises the first fiber grating 1, the second fiber grating 2, elastic body and hold-down arm, and elastic body is that what in a circular deformable body 3(the present embodiment, use is the circular deformable body of steel); Wherein the two ends of the first fiber grating 1 stick on the one side of circular deformable body 3, the two ends of the second fiber grating 2 stick on the another side of circular deformable body 3, the first fiber grating 1 is mutually vertical with the second fiber grating 2, and the grating of the two is all by the circle core shaft of circular deformable body 3 and do not contact; Described hold-down arm is fixed on the both sides of circular deformable body 3, is divided into the first hold-down arm 4 and the second hold-down arm 5, and with the first fiber grating 1 in same direction; The thickness of hold-down arm is slightly larger than the thickness of (diameter that thickness difference is greater than optical fiber) circular deformable body 3, and hold-down arm is provided with the fluting for the tail optical fiber through the first fiber grating 1.On circular deformable body 3, also there is fluting drawing for the second fiber grating 2 tail optical fibers.

When the curing end positions loading force F of the first fiber grating on circular deformable body, the dependent variable that the first fiber grating and the second fiber grating produce respectively:

$\left\{\begin{array}{c}{\mathrm{\ϵ}}_1=\frac{{\mathrm{\Δl}}_1}{2R}=\frac{{\mathrm{\π}}^2-8}{8\mathrm{\π}}\frac{{\mathrm{FR}}^2}{\mathrm{EI}}\\ {\mathrm{\ϵ}}_2=\frac{{\mathrm{\Δl}}_2}{2R}=-\frac{{\mathrm{\π}}^2-8}{8\mathrm{\π}}\frac{{\mathrm{FR}}^2}{\mathrm{EI}}\end{array}\right.---\left(1\right),$

In formula 1, ε ₁and ε ₂be the dependent variable that the first fiber grating and the second fiber grating produce, Δ l ₁with Δ l ₂be respectively the dependent variable that the first fiber grating and the second fiber grating produce, the elastic modulus that E is Shape-changeable ring, the internal-and external diameter average that R is circular Shape-changeable ring, I is the moment of inertia of Shape-changeable ring cross section face.

According to optical fiber Bragg raster axial strain sensing principle, the centre wavelength amount of movement of the first fiber grating and the second fiber grating is respectively:

$\left\{\begin{array}{c}\frac{{\mathrm{\Δ\λ}}_1}{{\mathrm{\λ}}_1}=(1-P_e){\mathrm{\ϵ}}_1+{\mathrm{\ΔT}}_1(\mathrm{\α}+\mathrm{\ξ})\\ \frac{{\mathrm{\Δ\λ}}_2}{{\mathrm{\λ}}_2}=(1-P_e){\mathrm{\ϵ}}_2+{\mathrm{\ΔT}}_2(\mathrm{\α}+\mathrm{\ξ})\end{array}\right.---\left(2\right),$

λ in formula ₁and λ ₂be respectively the centre wavelength of the first fiber grating and the second fiber grating, Δ λ ₁with Δ λ ₂be respectively the drift value of the first fiber grating and the second fiber bragg grating center wavelength, P _efor elasto-optical coefficient, Δ T ₁with Δ T ₂be respectively the temperature variation of the first fiber grating and the second fiber grating, consider that two gratings are under equivalent environment, can think Δ T ₁=Δ T ₂, introduce parameter the first fiber grating and the poor d=λ of the second fiber bragg grating center wavelength ₁-λ ₂, two equatioies subtract each other in above formula 2:

$\frac{{\mathrm{\Δd\λ}}_1-{\mathrm{\Δ\λ}}_{2}d}{{\mathrm{\λ}}_1{\mathrm{\λ}}_2}=(1-P_e)({\mathrm{\ϵ}}_1-{\mathrm{\ϵ}}_2)---\left(3\right),$

By the known Δ λ of grating parameter feature ₂d<< λ ₁λ ₂, omit event, and will in formula 1 substitution formula 3, obtain:

$\mathrm{\&Delta;d}=\frac{{\mathrm{\&pi;}}^2-8}{4\mathrm{\&pi;}}\frac{(1-P_e){\mathrm{\&lambda;}}_1{\mathrm{FR}}^2}{\mathrm{EI}}---\left(4\right),$

In formula, Δ d is the first fiber grating and the poor variable quantity of the second fiber bragg grating center wavelength, Δ λ ₂it is the variable quantity of the second fiber bragg grating center wavelength, obviously in formula 4 containing temperature term, the FBG strain gauge that utilizes this structure to make, the difference that makes two grating wavelength variable quantities only with the stressed big or small linear dependence of foil gauge, and temperature independent, eliminated the cross sensitivity of strain and temperature.

The method for making of above-mentioned fiber grating differential strain sheet is as follows: the two sides at circular deformable body arranges respectively a cross-notching, and the line of every cross-notching is all by the center of circular deformable body; Hold-down arm is fixed on the both sides of circular deformable body, and hold-down arm also arranges fluting, wherein a pair of being recessed on same straight line of the fluting of hold-down arm and circular deformable body; Through the first fiber grating of prestretched, along the fluting of circular deformable body one side, place, the fluting gluing that its grating is arranged on the circle core shaft of circular deformable body and its tail optical fiber is placed on circular deformable body and hold-down arm is fixed; Through the second fiber grating of prestretched, along the fluting of circular deformable body another side, place, the fluting gluing that its grating is arranged on the circle core shaft of circular deformable body and its tail optical fiber is placed on circular deformable body is fixed.

The using method of above-mentioned fiber grating differential strain sheet is: fiber grating differential strain sheet is fixed on monitored body by hold-down arm, utilizes following formula to obtain the stressed of fiber grating differential strain sheet:

$\mathrm{\&Delta;d}=\frac{{\mathrm{\&pi;}}^2-8}{4\mathrm{\&pi;}}\frac{(1-P_e){\mathrm{\&lambda;}}_1{\mathrm{FR}}^2}{\mathrm{EI}}.$

Adopt the direct bonding method in grating position, be difficult to guarantee the homogeneity of alite paste thickness in manufacturing process, very easily cause warbling of fiber grating, this will directly have influence on accuracy of detection.The mode that the present invention adopts two ends to paste, can guarantee that grating position is stressed evenly, eliminates warbling phenomenon, thereby has guaranteed the precision detecting, and the mode that paste at two ends also can make the manufacture craft of foil gauge simpler, is easier to operation.In the present invention, the first fiber grating and the second fiber grating must just can be pasted on circular deformable body in prestretched, can make like this foil gauge align negative strain and all can realize perception.

The present invention can change the sensitivity of foil gauge by changing the size (such as internal diameter, external diameter and thickness etc.) of circular deformable body, for being made into the foil gauge of different sensitivity, facilitate.In addition, it is stressed that the present invention utilizes hold-down arm to conduct, and in the time of can eliminating the monitored body of the direct contact of foil gauge, unbalance stress affects accuracy and the consistance of foil gauge.

Embodiment bis-:

The present embodiment structure and principle are all basic identical with embodiment mono-, and its difference is: described elastic body is hollow regular polygon deformable body.

The square of take is that square deformable body is example, and as shown in Figure 3 and Figure 4, it comprises the first fiber grating 1, the second fiber grating 2, elastic body, the first hold-down arm 4 and the second hold-down arm 5, and elastic body is a square deformable body 3; The installation method of the present embodiment is identical with the installation method of embodiment mono-.The present embodiment is fixed on monitored body by hold-down arm, utilizes following formula to obtain the differential variable quantity of raster center wavelength of fiber grating differential strain sheet:

$\mathrm{\&Delta;d}=\frac{(1-P_e){\mathrm{\&lambda;}}_1{\mathrm{Fa}}^2}{12\sqrt{2}\mathrm{EI}};$

In formula: Δ d is the first fiber grating and the poor variable quantity of the second fiber bragg grating center wavelength, and F is the stressed of fiber grating differential strain sheet, P _efor elasto-optical coefficient, λ ₁be the centre wavelength of the first fiber grating, a is the foursquare length of side, the elastic modulus that E is square deformable body, and I is the moment of inertia in square deformable body cross section.

Above embodiment is only for illustrating, if elastic body is hollow, not only rotational symmetry but also centrosymmetric deformable body all can reach object of the present invention.The scheme that FBG strain gauge of the present invention adopts, solved the problem of fiber grating pair strain and temperature cross sensitivity, when guaranteeing accuracy of detection, can also be easy to realize processing and fabricating, this provides strong support by the promotion and application for fiber grating sensing technology.

Claims (5)

1. a fiber grating differential strain sheet, is characterized in that: it comprises the first fiber grating, the second fiber grating, elastic body and hold-down arm, elastic body be a hollow, not only rotational symmetry but also centrosymmetric deformable body; Wherein the two ends of the first fiber grating stick on elastomeric one side, and the two ends of the second fiber grating stick on elastomeric another side, and the first fiber grating is mutually vertical with the second fiber grating, and the grating of the two is all by elastomeric center and do not contact; Described hold-down arm is fixed on elastomeric both sides, and with the first fiber grating in same direction; The thickness of hold-down arm is greater than elastomeric thickness, and hold-down arm is provided with the fluting for the tail optical fiber through the first fiber grating.

2. fiber grating differential strain sheet according to claim 1, is characterized in that: first, second fiber grating and elastomeric affixed points are respectively equipped with fluting.

3. fiber grating differential strain sheet according to claim 1, is characterized in that: described elastic body is circular deformable body or hollow regular polygon deformable body.

4. a method for making for the fiber grating differential strain sheet described in claim 1 or 2 or 3, is characterized in that:

On elastomeric two sides, one cross-notching is set respectively, the line of every cross-notching is all by elastomeric center;

Hold-down arm is fixed on elastomeric both sides, and hold-down arm also arranges fluting, the fluting of hold-down arm and elastomeric wherein a pair of being recessed on same straight line;

Through the first fiber grating of prestretched, along the fluting of elastic body one side, place, the fluting gluing that its grating is arranged on elastomeric central shaft and its tail optical fiber is placed on elastic body and hold-down arm is fixed; Through the second fiber grating of prestretched, along the fluting of elastic body another side, place, the fluting gluing that its grating is arranged on elastomeric central shaft and its tail optical fiber is placed on elastic strain sheet is fixed.

5. utilize the using method of the fiber grating differential strain sheet that the method for making of the fiber grating differential strain sheet described in claim 4 makes to be:

Fiber grating differential strain sheet is fixed on monitored body by hold-down arm, monitored body strain changes the deformation that causes Shape-changeable ring, and then make the first fiber grating and the second fiber bragg grating center wavelength is poor changes, by detecting two variable quantities that fiber bragg grating center wavelength is poor, draw the dependent variable that monitored body produces.