CN103673895A - Fiber Bragg grating micro-displacement sensor and measuring method thereof - Google Patents

Abstract

The invention discloses a fiber Bragg grating micro-displacement sensor and a measuring method thereof. The fiber Bragg grating micro-displacement sensor is composed of a cylindrical inner shell and an outer shell, four stainless steel flexible diaphragms are disposed in four symmetrical directions between the inner shell and the outer shell, places, in contact with the outer shell, of the flexible diaphragms are fixed by welding, the outer shell is fixed on the inner shell by the aid of pressure of the four flexible diaphragms, and fiber Bragg gratings are adhered on all of the four flexible diaphragms. The fiber Bragg gratings are placed horizontally, the inner shell is fixed, relative positions of the outer shell and the inner shell change in case that the outer shell is under the action of external micro-displacement changes, the diaphragms deform to drive the Bragg gratings thereon to deform, and wavelength of the fiber Bragg gratings shifts. Since the four diaphragms are different in deformation, size and direction of displacement changes can be judged by analysis of wavelength shift of the four Bragg gratings.

Description

Fiber Bragg Grating FBG micro-displacement sensor and measuring method thereof

Technical field

The invention belongs to technical field of optical fiber sensing, especially relate to a kind of column type Fiber Bragg Grating FBG micro-displacement sensor, belong to fiber optic sensing device.

Background technology

Fiber Bragg Grating FBG micro-displacement sensor is the strain sensitive characteristic according to Bragg grating, when Bragg grating is subject to axial strain effect, the space periodic of grating (being grating pitch) changes, bragg reflection wavelength will change, can centering heart wavelength shift by spectroanalysis instrument measure, can detect the size of change in displacement thus.Because fiber Bragg grating sensor has not only been inherited the various advantages of Fibre Optical Sensor, as simple in structure, volume is little, lightweight, anti-interference, anticorrosive etc., also there is the advantages such as Wavelength-encoding, wavelength-division multiplex.

Existing fiber grating displacement sensor can only detect the size of displacement, yet displacement is vector, and existing size also has direction, and this just not only needs to detect the size of displacement, also will reflect the sensor of the direction that displacement occurs simultaneously.

Summary of the invention

Technical matters to be solved by this invention is: a kind of Fiber Bragg Grating FBG micro-displacement sensor and measuring method thereof are provided, the present invention takes the mode that inside and outside shell is nested against one another and differential measurement combines, not only improve sensing sensitivity, and can judge the direction that displacement occurs simultaneously.

The technical solution adopted in the present invention is: a kind of Fiber Bragg Grating FBG micro-displacement sensor, comprise shell, inner casing, and inner casing is arranged on enclosure, is also provided with Fiber Bragg Grating FBG between inner casing and shell.

Further, shell and inner casing all adopt cylindrical.

Further, Fiber Bragg Grating FBG is arranged on flexible sheet.

Further, flexible sheet adopts stainless steel, and places on four symmetry directions between inner casing and shell.

Further, Fiber Bragg Grating FBG is around inner casing, and parallel with inner casing bottom surface.

Further, flexible sheet contacts with inner casing, and is welded on shell.

The measuring method of Fiber Bragg Grating FBG micro-displacement sensor, comprising:

Shell is subject to from the horizontal by θ angle, and size is after the displacement effect of h, by the bragg wavelength vertical direction drift value Δ λ of detection fiber Bragg grating _mN, horizontal direction drift value Δ λ _pQ, calculate respectively flexible sheet vertical direction variable quantity MN, horizontal direction variable quantity PQ, then according to following formula, calculate the size of h and θ:

$\left\{\begin{array}{c}h=\sqrt{{\mathrm{<figure-callout\; id="2"\; label="MN"\; filenames="HDA0000426552190000011.png,HDA0000426552190000012.png"\; state="\{\{state\}\}">MN</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="PQ"\; filenames="HDA0000426552190000011.png,HDA0000426552190000012.png"\; state="\{\{state\}\}">PQ</figure-callout>}}^2}\\ \mathrm{\&theta;}=\arctan \frac{\mathrm{MN}}{\mathrm{PQ}}\end{array}\right.$

Further, the Δ λ obtaining by detection _mN, Δ λ _pQ, the method for calculating MN, PQ is according to following two formulas:

MN=1/3.5*Δλ _MN

PQ=1/3.5*Δλ _PQ

Wherein, Δ λ _mN, Δ λ _pQunit be mm, the unit of MN, PQ is nm.

Advantage of the present invention: in order to realize the measurement of all directions micrometric displacement in plane, designed a kind of novel column type Fiber Bragg Grating FBG micro-displacement sensor, it adopts the column type inner core mode nested with shell, simple in structure, inner casing is fixed, shell produces change in displacement and acts on inner casing, due to the symmetry of cylinder, can effectively experience the displacement of all directions in plane.Introduced differential measurement method, two fiber gratings are as fiber grating pair simultaneously, and the difference changing according to two fiber grating reflection wavelengths not only can detect the size of displacement, can also judge the direction of displacement.

Accompanying drawing explanation

Fig. 1 is one-piece construction schematic diagram of the present invention.

Fig. 2 is cross sectional representation of the present invention.

Fig. 3 is stainless steel flexible sheet structural representation of the present invention.

Fig. 4 is the schematic diagram of embodiment of the present invention measuring method.

Description of reference numerals:

1-cylindrical shell 2-right cylinder inner casing 3-stainless steel flexible sheet 4-Bragg grating (FBG)

Embodiment

This fiber Bragg grating sensor is by column type inner casing, shell forms, on four symmetry directions between inner casing and shell, place four stainless steel flexible sheets, the place of flexible sheet and housing contacts is welded and fixed, utilize the pressure of four flexible sheets that shell is fixed on inner casing, on four flexible sheets, be all stained with Fiber Bragg Grating FBG, fiber grating horizontal positioned, inner casing is fixed, shell is subject to the effect that outside micrometric displacement changes, shell and inner casing relative position change, the generation deformation of diaphragm, drive Bragg grating generation deformation above, Fiber Bragg Grating FBG wavelength drifts about.Because the deformation of four diaphragms is different, can be by analyzing the size and Orientation of the wave length shift situation judgement change in displacement of four Bragg gratings.

Below in conjunction with concrete enforcement, the present invention is described in further detail.

The invention provides a kind of higher sensitivity that has, and can judge the column type Fiber Bragg Grating FBG micro-displacement sensor of displacement generation direction.Technical scheme of the present invention comprises: cylindrical inner casing, with the cylinder blanket that inner casing matches, on four symmetry directions between inner casing and shell, place four stainless steel flexible sheets.

In such scheme, inner casing is together with being pressed on by four stainless steel flexible sheets between shell.

In such scheme, optical fiber is close to and is surrounded on cylindrical inner casing, is parallel to inner casing bottom surface, is placed between shell and inner casing.

In such scheme, four stainless steel flexible sheets and column type housing contacts are partly welded and fixed.

Below in conjunction with drawings and Examples, be described in further detail the present invention.What Fig. 1 provided is column type Fiber Bragg Grating FBG micro-displacement sensor structural representation.

Embodiment:

Column type Fiber Bragg Grating FBG micro-displacement sensor, it comprises cylindrical shell 1, right cylinder inner casing 2, stainless steel flexible sheet 3 and Fiber Bragg Grating FBG 4, on four symmetry directions between inner casing 2 and shell 1, place 4 stainless steel flexible sheets 3, stainless steel flexible sheet 3 is welded and fixed with shell 1 contact portion, and right cylinder inner casing 2 is pressed in shell 1 by 4 stainless steel flexible sheets, is all stained with the Fiber Bragg Grating FBG 4 that sensing is used on stainless steel flexible sheet 3.

In the present embodiment, Fiber Bragg Grating FBG 4 sticks on the center of stainless steel flexible sheet 3, inner casing and shell are coupled mutually by flexible sheet, on 4 mutual symmetrical vertical inwalls that are welded on shell of stainless steel flexible sheet, stainless steel flexible sheet produces deformation under the change in displacement of shell, act on Fiber Bragg Grating FBG, two pairs of fiber gratings form differential measurement, a fiber grating is subject to strain aggravation, another fiber grating is subject to strain to be weakened, adopt differential structure, the difference changing by two fiber grating reflection wavelengths not only can detect the size of displacement, can also judge the direction of change in displacement, sensitivity is the twice of single-sensor.

Concrete measuring method is as follows:

What detect due to Bragg grating on two flexible sheets of symmetry is unidirectional change in displacement, for the convenience of analyzing, can only analyze the variation relation of two perpendicular diaphragms.As shown in the figure, while being subjected to displacement, the center of circle of inside and outside shell is not O point, if shell is subject to from the horizontal by θ angle, size is the displacement effect of h, the center of circle of shell moves to O ' point, the intersection point A point of vertical direction diameter and shell upper end moves to A ' point, and the intersection points B point of horizontal direction diameter and shell left end moves to B ' point.While being subjected to displacement, inner casing and upper horizontal diaphragm are not tangential on M point.Shell is subject to after displacement effect, if without inner casing squeezing action, M point moves to M ' point.Because inner casing is fixed, diaphragm edge and shell are fixed, diaphragm flexes and be still tangential on M point with inner casing.What measure is micrometric displacement, M point is still near the center of diaphragm, Bragg grating sticks near diaphragm center, can be similar to and think that effect that now Bragg grating is subject to is that variation MN in vertical direction causes, wherein N is crooked upper horizontal diaphragm two edges line and the intersection point of vertical direction diameter.

While in like manner, being subjected to displacement, inner casing and left vertical diaphragm are not tangential on P point.Shell is subject to after displacement effect, if without inner casing squeezing action, P point moves to P' point.Variation PQ in horizontal direction can be detected by the Bragg grating on the diaphragm of the left side, and wherein Q is crooked left vertical diaphragm two edges line and the intersection point of horizontal direction diameter.

Finally utilize fiber Bragg grating (FBG) demodulator, according to the drift value Δ λ of the bragg wavelength recording _mN(vertical direction) and Δ λ _pQ(horizontal direction) calculates respectively MN, PQ.Wherein, fiber Bragg grating (FBG) demodulator can not directly record the variation of displacement, can only reflect the variation of all directions wavelength value, records change in displacement and the Δ λ of MN, PQ direction in experiment _mNwith Δ λ _pQhave linear relationship, i.e. MN(mm)=(1/3.5) Δ λ _mN(nm), PQ(mm)=(1/3.5) Δ λ _pQ(nm).The variable quantity that Bragg grating in vertical direction and horizontal direction detects be respectively displacement in the vertical direction with horizontal direction on component, the size that can detect h and θ by the MN that detects and PQ like this.Can obtain:

$\left\{\begin{array}{c}h=\sqrt{{\mathrm{<figure-callout\; id="2"\; label="MN"\; filenames="HDA0000426552190000011.png,HDA0000426552190000012.png"\; state="\{\{state\}\}">MN</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="PQ"\; filenames="HDA0000426552190000011.png,HDA0000426552190000012.png"\; state="\{\{state\}\}">PQ</figure-callout>}}^2}\\ \mathrm{\&theta;}=\arctan \frac{\mathrm{MN}}{\mathrm{PQ}}\end{array}\right.$

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any modifications of doing within the spirit and principles in the present invention, be equal to and replace and improvement etc., within all should being included in protection scope of the present invention.

Claims (8)

1. Fiber Bragg Grating FBG micro-displacement sensor, is characterized in that: comprise shell (1), inner casing (2), inner casing (2) is arranged on shell (1) inside, between inner casing (2) and shell (1), is also provided with Fiber Bragg Grating FBG (4).

2. sensor according to claim 1, is characterized in that: shell (1) and inner casing (2) all adopt cylindrical.

3. sensor according to claim 1, is characterized in that: Fiber Bragg Grating FBG (4) is arranged on flexible sheet (3).

4. sensor according to claim 3, is characterized in that: flexible sheet (3) adopts stainless steel, and places on four symmetry directions between inner casing (2) and shell (1).

5. sensor according to claim 1, is characterized in that: Fiber Bragg Grating FBG (4) is around inner casing (2), and parallel with inner casing (2) bottom surface.

6. according to the sensor described in claim 3 or 4, it is characterized in that: flexible sheet (3) contacts with inner casing (2), and is welded on shell (1).

7. the measuring method of Fiber Bragg Grating FBG micro-displacement sensor, is characterized in that comprising:

Shell (1) is subject to from the horizontal by θ angle, and size is after the displacement effect of h, by the bragg wavelength vertical direction drift value Δ λ of detection fiber Bragg grating (4) _mN, horizontal direction drift value Δ λ _pQ, calculate respectively flexible sheet (3) vertical direction variable quantity MN, horizontal direction variable quantity PQ, then according to following formula, calculate the size of h and θ:

$\left\{\begin{array}{c}h=\sqrt{{\mathrm{MN}}^2+{\mathrm{PQ}}^2}\\ \mathrm{\&theta;}=\arctan \frac{\mathrm{MN}}{\mathrm{PQ}}\end{array}\right..$

8. method according to claim 7, is characterized in that: the Δ λ obtaining by detection _mN, Δ λ _pQ, the method for calculating MN, PQ is according to following two formulas:

MN=1/3.5*Δλ _MN

PQ=1/3.5*Δλ _PQ

Wherein, Δ λ _mN, Δ λ _pQunit be mm, the unit of MN, PQ is nm.

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