Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a fiber grating vibration sensor with temperature self-compensation and a method for manufacturing the same, in which the central wavelength variation of the fiber grating caused by temperature variation and the central wavelength variation of the fiber grating caused by stress generated by thermal expansion between the fixing points of the fiber grating due to distance variation are offset, so that the central wavelength of the fiber grating is not affected by temperature variation, and the temperature self-compensation of the fiber grating vibration sensor is realized.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
The fiber bragg grating vibration sensor with the temperature self-compensation comprises a mass block with a high thermal expansion coefficient, a base and an X-shaped flexible hinge with a low thermal expansion coefficient, wherein a shell is arranged on the base, the mass block and the X-shaped flexible hinge are wrapped by the shell, the mass block and the base are oppositely arranged at an upper-lower interval, the X-shaped flexible hinge is arranged between the mass block and the base, two ends of the X-shaped flexible hinge are respectively connected with the mass block and the base, fiber bragg gratings are axially arranged on the peripheries of the same side of the mass block and the base, and the fiber bragg gratings are located between the mass block and the base and are applied with prestress for detecting vibration in the vertical direction.
Further, the X-shaped flexible hinge at least comprises a pair of X-shaped flexible hinges, the X-shaped flexible hinges are arranged at intervals in parallel, bosses are respectively arranged at the upper end and the lower end of the X-shaped flexible hinge, grooves are formed in the lower end of the mass block and the upper end of the base, and the bosses are in plug-in fit with the corresponding grooves.
Further, an upper optical fiber groove is axially formed in the central axis of one side end face of the mass block, a lower optical fiber groove is axially formed in the central axis of one side end face of the base, the upper optical fiber groove is coaxial with the lower optical fiber groove, and tail fibers at two ends of the optical fiber grating are respectively fixed in the upper optical fiber groove and the lower optical fiber groove.
Further, the boss is a pin, the groove is a column hole, and the pin is in interference fit with the corresponding column hole.
Further, a fiber penetrating hole penetrating through the lower fiber groove is formed in the base, and a tail fiber at one end of the fiber bragg grating penetrates through the fiber penetrating hole and extends out of the base.
Further, the susceptor includes an upper substrate and a lower substrate, the upper substrate being laminated on the lower substrate, and an outer periphery of the lower substrate extending beyond an outer periphery of the upper substrate.
Further, the lower optical fiber groove is arranged on the upper substrate, and the fiber penetrating hole is arranged on the lower substrate and is communicated with the lower optical fiber groove.
Furthermore, the mass block and the base are both made of aluminum alloy, and the X-shaped flexible hinge is made of invar steel.
Further, the tail fibers at two ends of the fiber bragg grating are respectively fixed in the upper fiber groove and the lower fiber groove through epoxy resin, and at least the tail fibers in the epoxy resin are bare fibers.
The invention also provides a preparation method of the fiber grating vibration sensor with temperature self-compensation, which comprises the following steps,
S1, performing interference fit hot fitting on an X-shaped flexible hinge, a mass block and a base;
s2, after a certain prestress is applied to the fiber grating, tail fibers at two ends of the fiber grating are respectively fixed at the periphery of the mass block and the periphery of the base, the fiber grating is positioned between the mass block and the base, and tail fibers at least one end of the fiber grating extend out of the base;
and S3, assembling a shell on the base.
By adopting the technical scheme, the invention has the following advantages and effects:
The invention provides a fiber grating vibration sensor with temperature self-compensation and a preparation method thereof, which aim to solve the problem of strain and temperature cross sensitivity of the fiber grating vibration sensor during vibration measurement, through the selection of the sizes of the mass block, the base and the X-shaped flexible hinge and the thermal expansion coefficients of materials, the central wavelength variation of the fiber grating caused by temperature variation is offset with the central wavelength variation of the fiber grating caused by stress generated by distance variation caused by thermal expansion between the fiber grating fixed points, and finally the central wavelength of the fiber grating is not influenced by temperature variation, so that the temperature self-compensation of the fiber grating vibration sensor is realized.
Detailed Description
The following detailed description of the embodiments of the present invention will be provided with reference to the accompanying drawings in order to more clearly understand the objects, features and advantages of the present invention. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of the invention, but rather are merely illustrative of the true spirit of the invention.
As shown in fig. 1-4. The invention provides a fiber grating vibration sensor with temperature self-compensation, which comprises a mass block 2, a base 5 and an X-shaped flexible hinge 3, wherein a shell 1 is arranged on the base 5, the mass block 2 and the X-shaped flexible hinge 3 are wrapped by the shell 1, the mass block 2 and the base 5 are opposite in vertical interval, the X-shaped flexible hinge 3 is arranged between the mass block 2 and the base 5, and two ends of the X-shaped flexible hinge 3 are respectively connected with the mass block 2 and the base 5. An optical fiber grating 4 is axially arranged on the periphery of the same side of the mass block 2 and the base 5, the optical fiber grating 4 is positioned between the mass block 2 and the base 5 and is applied with prestress, and the optical fiber grating 4 is used for detecting vibration in the vertical direction. The fiber bragg grating 4 is used for respectively bonding and fixing the tail fibers at two ends of the fiber bragg grating on the mass block 2 and the base 5 through applying certain prestress, and one end of each tail fiber penetrates out of the base 5 and then is connected to the demodulator.
Specifically, the mass block 2 and the base 5 are made of materials with high thermal expansion coefficients, such as aluminum alloy or beryllium bronze, the mass block 2 has a cuboid structure, and the base 5 has a plate-shaped structure. The X-shaped flexible hinge 3 is made of a material with a low thermal expansion coefficient, such as quartz or invar.
The X-shaped flexible hinge 3 is an X-shaped structural member, and the X-shaped flexible hinge 3 is arranged between the mass block 2 and the base 5 to connect the mass block 2 and the base 5 into a whole. The bottom of the shell 1 is opened, screw holes are respectively formed in the periphery of the bottom of the shell 1, counter bores 504 are respectively formed in the periphery edges of the upper end of the base 5, and the shell 1 and the base 5 are fixed by penetrating the counter bores 504 through bolts 6 and being in threaded connection with the corresponding screw holes.
Further, the X-shaped flexible hinges 3 at least comprise a pair of X-shaped flexible hinges 3, the X-shaped flexible hinges 3 are arranged at intervals in parallel, bosses are respectively arranged at the upper end and the lower end of the X-shaped flexible hinges 3, grooves are formed in the lower end of the mass block 2 and the upper end of the base 5, and the bosses are fixedly connected with the mass block 2 and the base 5 after being in plug-in connection with the corresponding grooves. The boss and the groove are connected in a hot-fitting interference fit mode to realize reliable and stable connection of the X-shaped flexible hinge 3, the mass block 2 and the base 5.
Specifically, in order to ensure stability of the mass 2 and the base 5 while reducing torsional rigidity and lateral interference of the X-shaped flexible hinges 3, the X-shaped flexible hinges 3 may be provided in plurality, and the plurality of X-shaped flexible hinges 3 may be spaced apart from each other in parallel.
Preferably, the X-shaped flexible hinge 3 in the present invention comprises a pair of X-shaped flexible hinges 3 arranged in parallel and spaced side by side between the mass 2 and the base 5. Four grooves are formed in the lower end face of the mass block 2 and the upper end face of the base 5, bosses are arranged on the upper end face and the lower end face of the X-shaped flexible hinge 3, the four bosses on the upper end face of the pair of X-shaped flexible hinges 3 are in plug-in fit with the four grooves on the lower end face of the mass block 2, and the four bosses on the lower end face of the pair of X-shaped flexible hinges 3 are in plug-in fit with the four grooves on the upper end face of the base 5.
Further, in order to facilitate the fixation of the fiber grating 4, an upper fiber groove 202 is axially arranged at the central axis of one side end face of the mass block 2, a lower fiber groove 506 is axially arranged at the central axis of one side end face of the base 5, the upper fiber groove 202 and the lower fiber groove 506 are coaxial, and the pigtails at two ends of the fiber grating 4 are respectively adhered and fixed in the upper fiber groove 202 and the lower fiber groove 506.
Specifically, the upper optical fiber groove 202 and the lower optical fiber groove 506 are respectively positioned on the same side of the mass block 2 and the base 5 and are coaxially penetrated up and down, and the cross sections of the upper optical fiber groove 202 and the lower optical fiber groove 506 are preferably in a U-shaped structure.
Further, the boss is a pin 301, the groove is a pin hole, and the pin 301 is in interference fit with the corresponding pin hole.
Specifically, the pins 301 are preferably cylindrical pins, and the cylindrical holes are preferably cylindrical holes, and the pins 301 are provided on the upper and lower end portions of the X-shaped flexible hinge 3, respectively, integrally therewith. The column holes on the lower surface of the mass block 2 are upper column holes 201, and the upper column holes 201 are respectively matched with 4 pins 301 on the upper end surfaces of the pair of X-shaped flexible hinges 3 in a hole shaft connection mode. The column holes on the upper surface of the base 5 are lower column holes 505, and the lower column holes 505 are respectively in plug-in fit with 4 pins 301 on the lower end surfaces of the pair of X-shaped flexible hinges 3.
Further, a fiber penetrating hole 503 penetrating the lower fiber groove 506 is formed in the base 5, and the tail fiber of the fiber grating 4 penetrates through the fiber penetrating hole 503 and extends out of the lower end face of the base 5, and the extended tail fiber is connected with a fiber jumper and then connected to a demodulator.
Further, the susceptor 5 includes an upper substrate 502 and a lower substrate 501, the upper substrate 502 being laminated on the lower substrate 501, the outer periphery of the lower substrate 501 extending beyond the outer periphery of the upper substrate 502.
Specifically, the outer peripheral dimension of the upper substrate 502 is smaller than the outer peripheral dimension of the lower substrate 501, the upper substrate 502 is integrally provided with the lower substrate 501, the outer peripheral surface of the upper substrate 502 is coaxial with the outer peripheral surface of the lower substrate 501 when the upper substrate 502 is provided on the lower substrate 501, and the housing 1 is provided on the lower substrate 501 to surround the upper substrate 502.
Further, a lower optical fiber groove 506 is axially provided on the center axis of one end surface of the upper substrate 502, and a fiber penetration hole 503 is provided in the lower substrate 501 so as to penetrate the lower optical fiber groove 506. One end tail fiber of the fiber bragg grating 4 passes through the fiber penetrating hole 503 from the lower fiber groove 506 and then extends out of the lower substrate 501.
Further, the tail fibers at two ends of the fiber bragg grating 4 are respectively bonded and fixed in the upper fiber groove 202 and the lower fiber groove 506 through epoxy resin, and at least the tail fibers in the epoxy resin are bare fibers.
Specifically, in order to prevent the prestress on the fiber grating 4 from disappearing, the tail fiber adhered and fixed in the epoxy resin is a bare fiber section, and the bare fiber section is adhered and fixed to prevent the delamination phenomenon of the coating layer of the tail fiber, so that the prestress on the fiber grating 4 is released.
Further, in order to prevent the epoxy from overflowing, the glue dispensing grooves are formed at the bottoms of the positions where the upper optical fiber groove 202 and the lower optical fiber groove 506 are bonded and fixed with the pigtail, and the epoxy is filled in the glue dispensing grooves at the bottoms of the upper optical fiber groove 202 and the lower optical fiber groove 506, so that the epoxy can be prevented from overflowing along the upper optical fiber groove 202 or the lower optical fiber groove 506 when the pigtail is bonded and fixed with the epoxy.
As shown in fig. 5 and 6. The temperature compensation principle of the fiber grating vibration sensor is that an X-shaped flexible hinge 3 of the fiber grating vibration sensor is simplified into a bevel edge component, and a mass block 2 and a base 5 are simplified into a base component.
The length of the hypotenuse member is L1, the thermal deformation amount of the hypotenuse member after heating is dL1, the length of the hypotenuse member after heating is L1+dL1, the length of the base member is L2, the thermal deformation amount of the base member after heating is dL2, the length of the base member after heating is L2+dL2, the thermal expansion coefficients of the mass block 2 and the base 5 are alpha1, the thermal expansion coefficient of the X-type flexible hinge 3 is alpha2, the distance between the top of the base 5 and the bottom of the mass block 2 in the base member is h, the angle of the base member and the hypotenuse member when not rotating is theta, the relative rotation angle of the base member and the hypotenuse member is dtheta due to the thermal expansion of the hypotenuse member, and the angle of the base member and the hypotenuse member after heating is theta+dtheta.
When the ambient temperature increases, the base member expands in the horizontal direction by heat, so that the distance h between the top of the base 5 and the bottom of the mass 2 decreases. The thermal expansion of the hypotenuse member causes the relative rotation of the base member and the hypotenuse member to increase the distance h between the top of the pedestal 5 and the bottom of the mass 2, and the temperature sensing change of the distance between the top of the pedestal 5 and the bottom of the mass 2 is dh, so that the axial strain of the fiber grating 4The method comprises the following steps:;(1)
The thermal deformation of the hypotenuse member can be reduced when the hypotenuse member and the base member are rotated relatively to each other due to the change of the ambient temperatureDecomposing on XY two axes of rectangular coordinate system, thermal deformation amount of hypotenuse memberThe vector expression of (2) is:;(2)
Wherein, in the formula (2),Is a unit vector on the X-axis,Is a unit vector on the Y-axis,Is the angle between the hypotenuse member and the base member;
the amount of change in ambient temperature of the hypotenuse memberThermal deformation amount underExpressed as:;(3)
Wherein, in the formula (3),Is thatThe coefficient of thermal expansion in the direction (transverse direction),Is thatCoefficient of thermal expansion in the direction (longitudinal direction).
At this time, the coefficient of thermal expansion of the hypotenuse member in the rectangular coordinate system is definedThe method comprises the following steps:;(4)
Combining formulas (2) - (4), one can obtain:;(5)
the longitudinal thermal expansion coefficient of the obtained hypotenuse member (i.e. X-shaped flexible hinge 3) is arrangedThe method comprises the following steps:;(6)
since the fiber grating 4 can directly measure the sensed strain and temperature, the center wavelength of the fiber grating 4And the center wavelength shift of the fiber gratingExpressed as:;(7)
wherein, in the formula (7),The strain sensitivity obtained by actual measurement of the fiber bragg grating 4 is shown,For the temperature sensitivity obtained by the actual measurement of the fiber bragg grating 4,Is the effective elasto-optical coefficient of the optical fiber,Is the thermo-optic coefficient of the optical fiber,Is the coefficient of thermal expansion of the optical fiber.
In order to achieve the temperature compensation effect, the fiber grating vibration sensor should only receive the change of the ambient temperatureUnder the influence of (a) the center wavelength shift amount of the fiber bragg grating 40, I.e. satisfies:;(8)
The strain part in the center wavelength drift amount of the fiber bragg grating 4 is the center wavelength change generated by negative displacement between two fixed points of the fiber bragg grating 4 under the influence of temperature to compress the fiber bragg grating 4.
As shown in fig. 7. When the ambient temperature change isLength variation of the X-type flexible hinge 3 in the Y-axis directionThe method comprises the following steps:;(9)
wherein, in the formula (9),Is the torsional radius of the X-shaped flexible hinge 3,Is the half included angle of two straight beams of the X-shaped flexible hinge 3,And (3) withThe complementary angles are mutually complemented.
At this time, the equivalent strain amount generated by the axial compression of the fiber grating 4The method comprises the following steps:;(10)
At this time, the integral thermal expansion coefficient of the compensation part between the two fixed points of the fiber bragg grating, namely the longitudinal thermal expansion coefficient of the X-shaped flexible hinge 3, can be obtained by the formula (10)The method comprises the following steps:;(11)
wherein, in the formula (11),Is the distance between two fixed points of the fiber bragg grating. Based on formula (11), through selecting proper size and thermal expansion coefficient of the mass block 2, the base 5 and the X-shaped flexible hinge 3, the center wavelength of the fiber bragg grating 4 is not affected by temperature change, and temperature self-compensation of the fiber bragg grating vibration sensor is realized.
When the feasibility of the temperature compensation of the fiber bragg grating vibration sensor is verified, steady-state thermal simulation is carried out on a fiber bragg grating vibration sensor model through simulation software Ansys Workbench. During simulation, the initial environment temperature in steady-state thermal simulation is set to be 22 ℃, the working temperature of 42 ℃ is applied to the fiber bragg grating vibration sensor model, the temperature environment of the fiber bragg grating vibration sensor model is brought into a static mechanical analysis module, and thermal deformation of the fiber bragg grating vibration sensor model under the temperature rise condition of 20 ℃ can be obtained. Meanwhile, the solved boundary condition is that friction is not generated at the bottom of the fiber bragg grating vibration sensor model, and after the weak spring condition is applied, the relative displacement of the fiber bragg grating vibration sensor model at the sticking parts of the two ends of the fiber bragg grating is solved, so that the temperature compensation result of the fiber bragg grating vibration sensor model can be obtained.
Through comparison and simulation, the temperature drift amount of the fiber bragg grating vibration sensor can reach 0.64 pm/DEG C, and is effectively reduced compared with the temperature drift amount of the traditional single-mode fiber bragg grating by 10 pm/DEG C.
When the fiber grating vibration sensor is measured, the fiber grating vibration sensor is fixed on the surface of an object to be measured, the bottom surface of the fiber grating vibration sensor is kept at a vertical position, when the fiber grating vibration sensor is excited by external vibration, the mass block 2 of the fiber grating vibration sensor slightly rotates around the center of the X-shaped flexible hinge 3 under the action of inertia, the vertical displacement generated by the mass block 2 enables the fiber grating 4 to stretch or compress to cause the center wavelength drift of the fiber grating 4, the drift amount of the center wavelength of the fiber grating 4 is measured through a demodulator, and accordingly the corresponding relation between the external excitation acceleration and the drift amount of the center wavelength of the fiber grating is established, and vibration information of vibration acceleration is obtained.
The invention also provides a preparation method of the fiber grating vibration sensor with temperature self-compensation, which comprises the following steps,
And S1, performing interference fit hot fitting on the X-shaped flexible hinge 3, the mass block 2 and the base 5.
Specifically, during hot assembly, oil stains and dust on the matching surfaces of the base 5, the mass block 2 and the X-shaped flexible hinge 3 are cleaned, then the base 5 and the mass block 2 are heated for 15-20min, the temperature of the base 5 and the mass block 2 is raised to about 1000 ℃, the temperature is kept for 10min, and the hot assembly is immediately carried out after interference between the base 5 and the mass block and the upper end and the lower end of the X-shaped flexible hinge 3 is eliminated.
Step S2, after a certain prestress is applied to the fiber grating 4, tail fibers at two ends of the fiber grating 4 are respectively fixed in an upper fiber groove 202 at the periphery of the mass block 2 and a lower fiber groove 506 at the periphery of the base 5 by using epoxy resin, the fiber grating 4 is positioned between the mass block 2 and the base 5, and tail fibers at least one end of the fiber grating 4 extend out of the base 5.
Step S3, the shell 1 is assembled on the base 5, and the shell 1 is fixed on the base 5 through the bolts 6 during assembly.
It should be noted that the above-mentioned embodiments are merely for illustrating the technical solution of the present invention, and not for limiting the same, and although the present invention has been described in detail with reference to the above-mentioned embodiments, it should be understood by those skilled in the art that the technical solution described in the above-mentioned embodiments may be modified or some technical features may be equivalently replaced, and these modifications or substitutions do not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solution of the embodiments of the present invention.