CN1945217A - Optical fibre grating three dimensional forcel displacement sensor - Google Patents

Abstract

The optical fiber grating 3D force/displacement sensor includes 3 or more optical fiber gratings adhered to the surface of a cylinder axially in parallel in the same angle for use as basic sensor devices, monomode fibers to connect the optical fiber gratings to one optical branching device, one light source and one wavelength demodulator connected via monomode fibers to the optical branching device. When some force or displacement is applied to some point in the cylinder, these Bragg fiber gratings with different reflecting peaks with produce different drifts, so that the force or displacement may be calculated. Based on relevant material mechanics principles, the magnitude and direction of the force and displacement of the cylinder in 3D space may be calculated, and the 3D force and displacement may be sensed and measured.

Description

Optical fibre grating three-dimensional power/displacement transducer

[technical field]: the invention belongs to the sensing technology application, particularly a kind of optical fibre grating three-dimensional power or displacement transducer are mainly used in the sensing of space three-dimensional power and displacement.

[background technology]: fiber grating is a kind of novel photonic device, and it is the index distribution of a kind of space periodicity of setting up in optical fiber, can change and control the dissemination of light in optical fiber.Write the system Bragg grating on single-mode fiber, because uniform index distribution, its reflectance spectrum has a reflection peak that satisfies bragg condition, and the wavelength of reflection peak is directly proportional with the grid distance and the index modulation degree of depth.When fiber grating is subjected to axial force or displacement, its grid cycle will change, and then cause the drift of fiber grating reflection peak.Therefore can calculate suffered axial force of grating and displacement by the drift value of detection fiber optical grating reflection wavelength.

But, in the existing technology, only can do one dimension power sensing by using optical fibre grating, the scheme of using optical fibre grating implementation space three-dimensional force sensing is not arranged as yet.

[summary of the invention]: the objective of the invention is to solve the problem that the existing fiber grating sensor only can carry out one-dimensional measurement, a kind of optical fibre grating three-dimensional power/displacement transducer is provided.

Optical fibre grating three-dimensional power/displacement transducer provided by the invention, it is characterized in that being pasted on periphery with right cylinder axially parallel and equal angles as N fiber grating edge of pedestal sensor spare, wherein N is the natural number more than or equal to 3, N fiber grating is equal to the distance of right cylinder one end, one end of N fiber grating connects optical branching device by single-mode fiber, and the other end of optical branching device connects light source and Wavelength demodulation equipment respectively by single-mode fiber.

Fiber grating is the optical device that can be caused spectrum change by strain, is Bragg fiber grating, long period fiber grating, optical fiber FP chamber or fiber optic interferometric device.

Right cylinder is to constitute crooked girder construction, is semi-girder, free beam or elongation beam.

The fiber grating that is used for sensing adopts the connected mode of serial or parallel connection or string and series-parallel connection.

Light source is wideband light source or tunable optical source.

When somewhere on right cylinder applies power or displacement, three Bragg fiber gratings be because different its reflection peaks will produce different drift values, and then can calculate the power situation of three fiber grating positions.According to the relative theory of the mechanics of materials, can calculate stressed size and the direction that is in three-dimensional power and displacement of right cylinder.Can carry out the sensing measurement of three-dimensional force and displacement thus.

Test philosophy is:

If when right cylinder adopted semi-girder: length was L, and radius is R, and elastic modulus is that rigid cylindrical body one end of E is fixed, and an other end is unsettled, constituting xsect is circular semi-girder.Fiber grating with the spacing of hexagonal angle along cylinder axis to stickup.The distance of three fiber grating fixed distance ends is x.If when centre-point load F puts on free end, be set as follows coordinate system: the center of circle with the free end cross section is an initial point, with cylindrical be the z axle axially, with component F perpendicular to the power F on the z direction of principal axis _XyDirection be the y axle.Then three fiber grating positions in the xy plane in this coordinate system are on the circle of radius with R all being initial point with the center of circle.The angle of itself and F is respectively :-θ, 120 °-θ and 240 °-θ.

Then by the knowledge of the mechanics of materials as can be known, when semi-girder, only consider that bending has:

The moment of flexure at fiber grating place is:

M＝F _xy(L-x) (1)

Strain by distance center face y place on the cross section, fiber grating place is:

${\mathrm{\ϵ}}_{\mathrm{xy}}=\frac{\mathrm{\σ}}{E}=\frac{\mathrm{My}}{\mathrm{EI}}=\frac{(L-x)y{F}_{\mathrm{xy}}}{E\frac{\mathrm{\π}}{16}{R}^2}---\left(2\right)$

The axial strain of cylinder beam is:

${\mathrm{\ϵ}}_z=\frac{F_z}{E{\mathrm{\πR}}^2}---\left(3\right)$

Then the strain on each fiber grating is:

ε ₁＝αF _xycosθ+ε _z

ε ₂＝αF _xycos(120°-θ)+ε _z

ε ₃＝αF _xycos(240°-θ)+ε _z (4)

$\mathrm{\α}=\frac{L-x}{E\frac{\mathrm{\π}}{16}{R}^2}$

More than be principle analysis.When practical application, ε ₁, ε ₂, ε ₃Parameter (for known) for calculating by the wave length shift to fiber grating then by formula (4), can calculate size and the direction of F in three dimensions.

Simultaneously, according to the curved axis equation of semi-girder, can calculate free-ended lateral shift amount (direction and F _XyIdentical) be:

$w_{\mathrm{xy}}=\frac{F_{\mathrm{xy}}{L}^3}{3E\frac{\mathrm{\π}}{16}{R}^2}---\left(5\right)$

And axial displacement is:

$w_z={\mathrm{\ϵ}}_{z}L=\frac{F_z}{\mathrm{E\π}{R}^2}L---\left(6\right)$

Then can learn the size of free end at three-dimensional displacement.

If when right cylinder adopted free beam: length was L, and radius is R, and elastic modulus is that rigid cylindrical body one end (A) of E is fixed with hinge, an other end (B) is by stent support, and constituting xsect is circular free beam.Fiber grating with the spacing of hexagonal angle along cylinder axis to stickup.The distance of three fiber grating distance A ends is x.If centre-point load F puts on the position that the distance A end is a, and make a＞x.Be set as follows coordinate system: the center of circle with the A end section is an initial point, with cylindrical be the z axle axially, with component F perpendicular to the power F on the z direction of principal axis _XyDirection be the y axle.Then three fiber grating positions in the xy plane in this coordinate system are on the circle of radius with R all being initial point with the center of circle.The angle of itself and F is respectively :-θ, 120 °-θ and 240 °-θ.

Then by the knowledge of the mechanics of materials as can be known, when free beam, only consider that bending has:

The moment of flexure at fiber grating place is:

$M=F_{\mathrm{xy}}\frac{(L-a)}{L}x---\left(7\right)$

Strain by distance center face y place on the cross section, fiber grating place is:

${\mathrm{\ϵ}}_{\mathrm{xy}}=\frac{\mathrm{\σ}}{E}=\frac{\mathrm{My}}{\mathrm{EI}}=\frac{\frac{(L-a)}{L}\mathrm{xy}{F}_{\mathrm{xy}}}{E\frac{\mathrm{\π}}{16}{R}^2}---\left(8\right)$

The axial strain of cylinder beam is:

${\mathrm{\ϵ}}_z=\frac{F_z}{\mathrm{E\π}{R}^2}---\left(9\right)$

Then the strain on each fiber grating is:

ε ₁＝αF _xycosθ+ε _z

ε ₂＝αF _xycos(120°-θ)+ε _z

ε ₃＝αF _xycos(240°-θ)+ε _z (10)

$\mathrm{\α}=\frac{\frac{(L-a)}{L}x}{E\frac{\mathrm{\π}}{16}{R}^2}$

More than be principle analysis.When practical application, ε ₁, ε ₂, ε ₃Parameter (for known) for calculating by the wave length shift to fiber grating then by formula (4), can calculate size and the direction of F in three dimensions.

Simultaneously, according to the curved axis equation of free beam, can calculate lateral shift amount (direction and the F at stressed place _XyIdentical) be:

$w_{\mathrm{xy}}=\frac{F_{\mathrm{xy}}\mathrm{ba}}{6E\frac{\mathrm{\π}}{16}{R}^{2}L}(2a^2-2\mathrm{aL})---\left(11\right)$

And axial displacement is:

$w_z={\mathrm{\ϵ}}_{z}L=\frac{F_z}{\mathrm{E\π}{R}^2}L---\left(12\right)$

Then can learn the stressed size that is in three-dimensional displacement.

Advantage of the present invention and effect: the present invention is to provide a kind of novel optical fiber and optical grating three-dimensional force/displacement transducer, utilize bragg grating as senser element, adopt three or above fiber grating to form the space sensor array, by to the correlation analysis implementation space three-dimensional force of three fiber grating reflection wavelength peak shift amounts and the measurement of displacement.

[description of drawings]:

Fig. 1 is optical fibre grating three-dimensional power of the present invention/displacement sensor structure synoptic diagram.

[embodiment]:

Embodiment 1:

As shown in Figure 1, optical fibre grating three-dimensional power/displacement transducer provided by the invention comprises: light source 1, Wavelength demodulation equipment 2, optical branching device 3, optical fibre optical grating sensing array 4, right cylinder 5, single-mode fiber 6.Three fiber gratings, 4 edges as pedestal sensor spare are pasted on periphery with right cylinder 5 axially parallels and equal angles (120 degree), wherein N gets three (also desirable more than three), three fiber gratings equate (as getting 1/2 cylinder length) to the distance of right cylinder one end, one end of three fiber gratings connects optical branching device 3 by single-mode fiber 6, and the other end of optical branching device connects light source 1 and Wavelength demodulation equipment 2 respectively by single-mode fiber.

By to the drift value calculating place right cylinder of each optic fiber grating wavelength the size and Orientation of stressed and displacement.

Wherein, light source 1 can be wideband light source or narrow-band tunable light source.

Wavelength demodulation equipment 2 can be spectrometer or multi-wavelength meter isophotal wavelength demodulated equipment.

Optical branching device 3 can be optical device such as photo-coupler, photoswitch.

Optical fiber force transducer 4 can be the fiber grating force sensor array.

Right cylinder 5 can be the right cylinder of the even metal of quality, nonmetal or other materials.

Embodiment 2:

The service band of light source 1 is the wideband light source of 1530-1560nm.It is the coupling mechanism of 1550nm wave band that optical branching device 3 adopts service band.Optical wavelength detuner 2 adopts spectroanalysis instrument.The centre wavelength of optical fiber optical grating array 4 is respectively 1540.000nm, 1545.000nm, 1550.000nm.Single-mode fiber 6 adopts the single-mode fiber of 1550nm wave band.Cylindrical length is 10cm, and radius is 1cm, and material therefor is an organic glass, elastic modulus E=2700.

When practical application, light source 1 is linked to each other with optical branching device 3, optical branching device 3 and optical fibre optical grating sensing array 4, optical branching device 3 and wavelengt demodulator 2 with single-mode fiber 6.Adopt three fiber gratings to constitute optical fiber optical grating array 4 and be pasted on cylindrical middle part respectively, distance circle cylinder two ends distance equates.Simultaneously, three fiber gratings are mutually 120 degree angles.Right cylinder one end is fixed, and the other end is a free end, constitutes semi-girder.Power F acts on the free end of beam.Then can be by aforementioned principles, by the drift value to the Optical Fiber Sensing Array wavelength calculate right cylinder stressed size and Orientation.

As: when the free end of the power F that applies a three-dimensional at semi-girder.If the wave length shift that obtains three fiber gratings by the spectral measurement device measuring be respectively 0.1nm ,-0.05nm ,-0.05nm, then the strain value of corresponding each fiber grating is 100 μ ε ,-50 μ ε ,-50 μ ε.Then will these cylindrical structural parameters and the formula (4) of the aforementioned cantilever beam structure of each fiber grating strain value substitution, can calculate α=1.886, F _Xy=53N, F _z=0, θ=0.The direction that then can obtain power F is θ=0, and its size is 53N.

Claims (6)

1. optical fibre grating three-dimensional power/displacement transducer, it is characterized in that being pasted on periphery with right cylinder axially parallel and equal angles as N fiber grating edge of pedestal sensor spare, wherein N is the natural number more than or equal to 3, N fiber grating is equal to the distance of right cylinder one end, one end of N fiber grating connects optical branching device by single-mode fiber, and the other end of optical branching device connects light source and Wavelength demodulation equipment respectively by single-mode fiber.

2. optical fibre grating three-dimensional power/displacement transducer according to claim 1, it is characterized in that: fiber grating is the optical device that can be caused spectrum change by strain, is Bragg fiber grating, long period fiber grating, optical fiber FP chamber or fiber optic interferometric device.

3. optical fibre grating three-dimensional power/displacement transducer according to claim 1 and 2 is characterized in that: right cylinder is semi-girder, free beam or elongation beam for constituting crooked girder construction.

4. optical fibre grating three-dimensional power/displacement transducer according to claim 1 and 2 is characterized in that: the fiber grating that is used for sensing adopts the connected mode of serial or parallel connection or string and series-parallel connection.

5. optical fibre grating three-dimensional power/displacement transducer according to claim 1 and 2 is characterized in that: light source is wideband light source or tunable optical source.

6. optical fibre grating three-dimensional power/displacement transducer according to claim 1 and 2 is characterized in that: utilize this principle, the measurement of carry out three dimensional strain, shearing physical quantity.