CN102230834A - Fiber grating cable tension transducer with temperature self-compensation function - Google Patents

Abstract

The invention provides a fiber grating cable tension transducer with a temperature self-compensation function, belonging to the field of transducer technologies. The transducer provided by the invention is characterized by comprising a metal baseplate, a clamping piece, a micro fiber grating strain transducer and a cable component of fiber transmission. The measuring sensitivity of the transducer can be adjusted by changing sizes of elements of the transducer in accordance with actual requirements, thus being suitable for monitoring cable tension of the different cables in real time. The fiber grating cable tension transducer can measure the cable tension of the cables indirectly by measuring an anchor head structure and utilize the properties of the fiber grating to improve the cable tension sensitivity coefficients of the transducer, and is not influenced by structural materials and external environments. The fiber grating cable tension transducer can eliminate influences of eccentric forces on measuring values, realize the temperature self-compensation and overcome the defects that a traditional electric transducer is subjected to electromagnetic interference easily and is poor in long-term stability, and has the advantages of high accuracy, light weight, low influences on the properties of the structure and the like.

Description

A kind of Fiber Bragg Grating Cable Tension Sensor with temperature self-compensation

Technical field

The invention belongs to tension measurement technical field of tools, relate to a kind of cable force sensor, be specially adapted to cable load-carrying members such as gymnasium, stadium, cable-stayed bridge, suspension bridge based on Fiber Bragg Grating technology based on sensing technology.

Background technology

Flexible systems such as suspended-cable structure, membrane structure and rope one membrane structure are all resisted external load with tension force effect can be generically and collectively referred to as tension structure.Cable is as the crucial primary structure member of tension structure, and is closely related between the dynamic response of its stress and dynamic response and main structure body, and the stress of rope and kinematic behavior are to weigh the important parameter whether structure is in normal condition.Yet owing to reasons such as structural design, extraneous corrosion and fatigue accumulation, damage and deterioration in various degree can appear in cable in-service unavoidably.Therefore, adopting the real-time monitoring implementation structure security performance assessment of cable is the developing direction of following tension structure safety assessment.

Fiber grating is nearly decades of a kind of novel full fiber optic passive devices with the fastest developing speed, is the strain transducer of sensing element development with the fiber grating, has highly sensitive, advantages such as volume is little, corrosion-resistant, anti-electromagnetic-radiation interference; Overcome the short shortcoming of traditional electrical sensor long-time stability difference and signal transmission distance, can realize the real-time monitoring of tension structure cable state.And a plurality of fiber gratings can also be formed quasi-distributed sensor-based system, adopt an optical cable just can realize quasi-distributed measurement.

The gluing method of attachment of tradition is owing to existing the problem of aging of glue, so can not guarantee stability, the reliability requirement of long term monitoring.Because the safe handling requirement of steel wire in the cable, any destructive, operation that might influence its intensity can not be carried out in the surface, consider cable manufacture craft, progress and sensor cost problem in addition, therefore can not take fiber Bragg grating strain sensor directly is placed on the mode that links into an integrated entity such as direct and steel wire in the cable body.

Summary of the invention

The technical problem to be solved in the present invention just provided a kind of can be under the prerequisite of not destroying steel wire, take all factors into consideration and do not disturb the cable manufacture craft, do not delay cable making progress and make every effort to problems such as the sensor cost is lower, fiber Bragg grating strain sensor is welded on the stressed less position of anchor head, the cable body pulling force can accurately be delivered on the fiber Bragg grating strain sensor on the anchor head.The character of fiber grating self of utilizing this sensor has improved the pulling force sensitivity coefficient of sensor, is not subjected to the influence of material; The measurement sensitivity of sensor simultaneously can be adjusted by changing size of devices according to the actual requirements, can be applicable to that the Suo Li of variety classes cable in the building structure monitors in real time.

Technical scheme of the present invention is as follows:

At first according to the principle of work of fiber grating as can be known, the wavelength variations Δ λ of fiber grating and the relational expression of strain stress are formula (1):

Δλ＝K _ε·ε (1)

K in (1) formula of being somebody's turn to do _εBe the fiber Bragg grating strain sensor sensitivity coefficient.For fibre core is the optical fiber situation of pure quartz, and centre wavelength is near the fiber grating K the 1550nm _εEqual 1.2pm/ μ ε.

According to the mechanics of materials, when on the anchor head during the eccentric pulling force of effect shown in Fig. 2 (a), the eccentric tensile force f that acts on arbitrfary point a can be converted into the equivalent load shown in Fig. 2 (b), promptly act on the tensile force f at anchor head center ' with couple Fx, Fy.Under the coordinate system that Fig. 2 (b) is set up, couple Fx, Fy are respectively Mx, My, Mx=Fy, My=Fx to the effect of anchor head.

If the elastic modulus of anchor head is E, the external diameter that fiber Bragg grating strain sensor position anchor head is installed is R, and cross-sectional area is A, and elastic modulus is E, and the material cross-section moment of inertia is I, and then the strain of 4 strain transducer correspondence positions is respectively:

$\left.\begin{array}{c}{\mathrm{\ϵ}}_1=(\frac{F^{\′}}{\mathrm{EA}}-\frac{\mathrm{MyR}}{\mathrm{EI}})\cos \mathrm{\α},{\mathrm{\ϵ}}_2=(\frac{F^{\′}}{\mathrm{EA}}-\frac{\mathrm{MxR}}{\mathrm{EI}})\cos \mathrm{\α}\\ {\mathrm{\ϵ}}_3=(\frac{F^{\′}}{\mathrm{EA}}+\frac{\mathrm{MyR}}{\mathrm{EI}})\cos \mathrm{\α},{\mathrm{\ϵ}}_4=(\frac{F^{\′}}{\mathrm{EA}}+\frac{\mathrm{MxR}}{\mathrm{EI}})\cos \mathrm{\α}\end{array}\right\}---\left(2\right)$

α is the angle of anchor head outside surface and its axis in the formula (2), order

$\mathrm{\&epsiv;}=\frac{1}{4}({\mathrm{\&epsiv;}}_1+{\mathrm{\&epsiv;}}_2+{\mathrm{\&epsiv;}}_3+{\mathrm{\&epsiv;}}_4)=\frac{\mathrm{<figure-callout\; id="4"\; label="F"\; filenames="HSA00000516592900012.png"\; state="\{\{state\}\}">F</figure-callout>}}{4\mathrm{EA}}\cos \mathrm{\&alpha;}---\left(3\right)$

In the following formula, ε is the mean value of four sensor correspondence positions strain, then has

$F=\frac{4\mathrm{\&pi;<figure-callout\; id="2"\; label="E\; R"\; filenames="HSA00000516592900012.png"\; state="\{\{state\}\}">E</figure-callout>}{R}^{}{}^2\mathrm{\&epsiv;}}{\cos \mathrm{\&alpha;}}---\left(4\right)$

Can be obtained by (4) formula, as long as guarantee 4 sensors in same xsect, then strain stress is a certain value.Order

Then (4) formula can be write as following formula (5) F=K ε; By (5) formula as can be seen, the strain of Suo Li and anchor head arbitrary surfaces is linear, so the method that can adopt fiber Bragg grating strain sensor to measure strain is measured Suo Li.

Aspect strain measurement, adopt the packaged type that fiber grating is carried out the two ends clamping, the length L of optical fiber between distance L that this packaged type can be by adjusting the two ends fixed pivot and the two ends package parts _fBetween ratio relation change the sensitivity coefficient of sensor.In sensor construction, the strain of hold assembly can be ignored, so the deflection between fixed pivot almost all is carried on the optical fiber.Be in the fiber grating of the left back wave band of 1550nm for centre wavelength, the center wavelength variation of sensor and the relation of extraneous strain are as shown in the formula (6):

With (6) formula band people (4) formula, can get formula (7):

Wherein

Work as K _fOne regularly, and the wavelength variations Δ λ of Suo Li F and fiber Bragg grating strain sensor is linear, and can be by changing L _fAnd the ratio between L is realized the adjustment of cable tension sensor measurement sensitivity.According to above principle, utilize Fiber Bragg Grating Cable Tension Sensor of the present invention, just can monitor the Suo Li of various tension structure cables easily in real time.

Consider temperature effect, can get that hoop strain ε ' and axial strain ε satisfy Poisson ratio formula (8) according to the mechanics of materials

Order $\stackrel{\&OverBar;}{\mathrm{\&Delta;\&lambda;}}=\frac{1}{4}\underset{i=1}{\overset{4}{\mathrm{\&Sigma;}}}{\mathrm{\&Delta;\&lambda;}}_i$

Bringing formula (8) into formula (6) gets

Be located under the acting in conjunction of strain and temperature, then the wavelength variations of 5 fiber Bragg grating strain sensor correspondences is

$\left.\begin{array}{c}\stackrel{\&OverBar;}{\mathrm{\&Delta;\&lambda;}}=\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{\&lambda;}}_F}+{\mathrm{\&Delta;\&lambda;}}_T\\ {\mathrm{\&Delta;\&lambda;}}_5=-\frac{\mathrm{\&mu;}\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{\&lambda;}}_F}}{\cos \mathrm{\&alpha;}}+{\mathrm{\&Delta;\&lambda;}}_T\end{array}\right\}---\left(9\right)$

Δ λ in the formula _FBe the wavelength variations value of fiber grating under the pulling force effect, Δ λ _TWavelength variations value for fiber grating under the temperature effect.

Then have $\stackrel{\&OverBar;}{{\mathrm{\&Delta;\&lambda;}}_F}=\frac{\stackrel{\&OverBar;}{\mathrm{\&Delta;\&lambda;}}-{\mathrm{\&Delta;\&lambda;}}_5}{1+\frac{\mathrm{\&mu;}}{\cos \mathrm{\&alpha;}}}---\left(10\right)$

Bring (10) formula into (7) Shi Kede:

$F=K(\stackrel{\&OverBar;}{\mathrm{\&Delta;\&lambda;}}-{\mathrm{\&Delta;\&lambda;}}_5)---\left(11\right)$

Formula (11) is the principle of work of the Fiber Bragg Grating Cable Tension Sensor of rejecting temperature effect, and the suffered Suo Li F of cable is directly proportional scale-up factor with strain transducer wave length shift algebraic sum

K also can be determined by the Suo Li calibration experiment of Fiber Bragg Grating Cable Tension Sensor.

This cable tension sensor is by to the measurement of cable anchor head position strain and then obtain cable force, it is improved one's methods and is 4 clipping fiber Bragg grating strain sensors are arranged symmetrically in the anchor head corresponding site, to eliminate the influence of eccentric moment, and, realized on-line real time monitoring quickly and easily to cable force not delaying cable making progress with not damaging under the prerequisite of cable body steel wire; Arrange a strain transducer along the anchor head hoop simultaneously, realize temperature compensation cable tension sensor.

Effect of the present invention and benefit have provided the contact type optical fiber grating cable tension sensor that a kind of surface strain variations based on the cable anchor head is monitored cable force in real time, it has, and cost is lower, principle is simple, easy for installation, to advantages such as cable cable body steel wire are harmless.In addition, the present invention can well eliminate the influence of eccentric pulling force to measured value, and can realize temperature self-compensation; Overcome traditional electrical sensor simultaneously and be subject to shortcomings such as electromagnetic interference (EMI), long-time stability difference, have precision height, little, the light weight of volume, to advantage such as the property effect of structure self is little.Thereby can realize that to cable online in real time cable force monitoring for improving the structural entity security, reduce potential safety hazard and operation risk, increasing economic efficiency has positive meaning.

Description of drawings

Accompanying drawing 1 is a drag-line anchor head side view.

Accompanying drawing 2 (a) is the drag-line anchor head sectional view that is subjected to eccentric pulling force, and accompanying drawing 2 (b) is the drag-line anchor head sectional view that eccentric pulling force is converted into equivalent load.

Accompanying drawing 3 is Fiber Bragg Grating Cable Tension Sensor encapsulating structure figure.

Among the figure: 1 fiber grating, 2 package parts, 3 hold assemblies, 4 fixed parts, 5 optical fiber, 6 steel pipes, 7 steel pipes, 8 steel pipes, 9 steel pipes.

Embodiment

Be described in detail the specific embodiment of the present invention below in conjunction with technical scheme and accompanying drawing.

Embodiment 1

The synoptic diagram of Fiber Bragg Grating Cable Tension Sensor encapsulating structure of the present invention respectively as shown in figures 1 and 3.The encapsulating structure of Fiber Bragg Grating Cable Tension Sensor comprises metal base plate, holding piece, mini optical fibre grating strain transducer and transmission cable.Sensor is installed in the stressed less position of cable anchor head by metal base plate, and holding piece is fixed on the mini optical fibre grating strain transducer on the metal base plate by bolt, and metal base plate can be changed different shapes according to the difference of anchor head structure.

This Fiber Bragg Grating Cable Tension Sensor is made up of fiber grating 1, package parts 2, hold assembly 3 and fixed part 4; Adopt the method for glueing joint to be fixed in the package parts 2 at fiber grating 1 two ends, then package parts 2 are placed respectively in the hold-down support 4, and use bolt that hold assembly 3 tightly is connected with hold-down support 4, use the mode of welding that hold-down support 4 is connected with anchor head at last;

It is as follows that described fiber Bragg grating strain sensor is made method for packing: at first peel off the wherein overlay on optical fiber 5 surfaces of an end of fiber grating 1, use the fiber coating machine that bare optical fibers and bare optical gratings 1 position is applied, after waiting to solidify fiber grating placed steel pipe 6 and steel pipe 7, use accurate fiber adjusting mount to adjust its position, make it be in central part, then pour into the epoxide-resin glue that configures by a certain percentage, treat that evenly the capillary tubing 6 and the steel pipe 7 of coating place respectively in steel pipe 8 and the steel pipe 9 with outer wall after the adhesive curing, treat adhesive curing, then two hold assemblies 3 are inserted in respectively in the package parts 2 at fiber grating two ends, pour into bonding hold assembly 3 of epoxide-resin glue and package parts 2, treat promptly to finish encapsulation after the epoxy resin adhesive curing.

Claims (2)

1. Fiber Bragg Grating Cable Tension Sensor with temperature self-compensation, form by fiber grating (1), package parts (2), hold assembly (3) and fixed part (4), it is characterized in that: adopt the method for glueing joint to be fixed in the package parts (2) at fiber grating (1) two ends, then package parts (2) are placed respectively in the hold-down support (4), and use bolt that hold assembly (3) is linked to each other with hold-down support (4), use the mode of welding that hold-down support (4) is connected with anchor head at last; It is as follows that described fiber Bragg grating strain sensor is made method for packing: at first peel off the wherein overlay on the optical fiber of an end (5) surface of fiber grating (1), use the fiber coating machine that bare optical fibers and bare optical gratings (1) position is applied, after waiting to solidify fiber grating placed steel pipe (6) and steel pipe (7), use accurate fiber adjusting mount to adjust its position, make it be in central part, then pour into the epoxide-resin glue that configures by a certain percentage, treat that evenly the capillary tubing (6) and the steel pipe (7) of coating place respectively in steel pipe (8) and the steel pipe (9) with outer wall after the adhesive curing, treat adhesive curing, then two hold assemblies (3) are inserted in the package parts (2) at fiber grating two ends respectively, pour into bonding hold assembly of epoxide-resin glue (3) and package parts (2), treat promptly to finish encapsulation after the epoxy resin adhesive curing.

2. a kind of Fiber Bragg Grating Cable Tension Sensor according to claim 1 with temperature self-compensation, its feature also is: adopt four fiber Bragg grating strain sensors to eliminate the influence of eccentric moment simultaneously, the central angle of two adjacent fiber Bragg grating strain sensors is 90 °; Arrange a clipping fiber Bragg grating strain sensor along cable anchor head hoop direction, realize temperature compensation cable tension sensor.

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