CN114705885B - Fiber bragg grating acceleration sensor of stepped cantilever beam and measuring method thereof - Google Patents
Fiber bragg grating acceleration sensor of stepped cantilever beam and measuring method thereof Download PDFInfo
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- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
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- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
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Abstract
The fiber grating acceleration sensor comprises a fiber grating, two fiber gratings, an equal-thickness beam, a second-thickness beam, a base and a mass block; the top end and the bottom end of the base are respectively provided with a fiber guide groove and two fiber guide grooves; the top end and the bottom end of the mass block are respectively provided with three fiber guide grooves and four fiber guide grooves; the bottoms of the first fiber guide groove and the third fiber guide groove are positioned on the same horizontal plane, and the bottoms of the second fiber guide groove and the fourth fiber guide groove are positioned on the same horizontal plane; the middle part of the side surface of the base is connected with a second-class thickness beam, the middle part of the side surface of the mass block is connected with a first-class thickness beam, and the second-class thickness beam is connected with the first-class thickness beam; the first-class thickness beam and the second-class thickness beam form a stepped cantilever beam. The invention applies prestress when the fiber grating is installed, avoids the fiber grating from being damaged when being stretched or compressed, and prolongs the service life of the sensor; the influence of temperature on the measurement result is solved, and the accuracy of the measurement result is ensured to be higher.
Description
Technical Field
The invention relates to a mechanical vibration measurement technology, belongs to the field of mechanical measurement, and particularly relates to a fiber bragg grating acceleration sensor of a stepped cantilever beam and a measurement method thereof.
Background
Vibration measurement of mechanical equipment has been an important issue in the engineering field. Mechanical equipment is easy to generate mechanical faults in the long-term operation process, and once the mechanical equipment fails, the working state of the mechanical equipment is affected, and serious safety accidents are caused to cause serious losses of personnel and property. Moreover, many mechanical equipment failures are highly correlated to their low frequency vibrations. The mechanical equipment fault can be timely and accurately diagnosed and predicted through the analysis of the mechanical equipment vibration information, and the method has very important significance for improving the operation stability, safety and economy of the mechanical equipment.
Conventional vibration monitoring sensors are mostly eddy current sensing and photoelectric sensors. In low frequency vibration signal measurement, eddy current sensors have significant limitations: first, the excessively high resistance of the induction coil material of the eddy current sensor will result in a low linear measurement range and quality factor of the sensor, severely affecting the measurement result of the low frequency vibration signal. And secondly, the temperature stability of the eddy current sensor is poor, the electromagnetic interference resistance is low, and the eddy current sensor is not suitable for the working environment of a high-temperature strong magnetic field. Furthermore, the traditional eddy current sensor is affected by the structural parameters of the coil, so that the sensitivity and linearity of the eddy current sensor are poor, the precision of the eddy current sensor is poor under a sudden change temperature field, and the detected low-frequency signal is distorted. The photoelectric sensor measures the position or displacement of the object by comparing the intensity of emitted light with that of received light based on the optical principle. The light receiving device has high requirements, and a strong reflector needs to be arranged on the surface of the measured object to strengthen the intensity of reflected light. However, in practical applications, vibration of the mechanical device will cause the reflection lens to fall off or be damaged, which seriously affects the service life of the sensor. And the photoelectric sensor is influenced by dust, so that the error is overlarge when measuring low-frequency vibration, and the accuracy of a measurement result is seriously influenced. In summary, the eddy current sensor and the photoelectric sensor have the capability of low-frequency vibration detection, but are affected by the external environment and the structure thereof, so that the precision and the sensitivity cannot meet the requirement of low-frequency vibration detection.
The fiber bragg grating acceleration sensor is widely used for on-line health monitoring of large-scale equipment and engineering in severe environments such as aerospace, subway tunnels, bridge structures, coal mines and the like by virtue of the advantages of no electromagnetic interference, long-distance transmission, long service life, distributed networking and the like. Based on the vibration characteristics of the cantilever beam, the fiber grating acceleration sensor of the cantilever beam becomes one of the research directions with the most development prospect in the detection of low-frequency vibration signals. The core sensitive component of the fiber bragg grating acceleration sensor is a fiber bragg grating, and an acceleration and frequency measuring unit is formed by sensing strain by the fiber bragg grating and combining a mechanical structure. The fiber grating acceleration sensor of the stepped cantilever beam obtains good sensitivity and low-frequency response by changing the rigidity and effective mass distribution of the cantilever beam structure, and is suitable for mechanical assembly.
In summary, aiming at the problems that in the prior art, the influence of temperature on the wavelength of the fiber grating and the cross sensitivity of the fiber grating and the temperature are caused by the change of the ambient temperature, and the accuracy of a low-frequency vibration signal is seriously influenced, no good sensor can overcome the influence of the temperature and realize high-precision vibration signal measurement when detecting the low-frequency vibration signal.
The disclosure of this background section is only intended to increase the understanding of the general background of the present patent application and should not be taken as an admission or any form of suggestion that this information forms the prior art already known to a person of ordinary skill in the art.
Disclosure of Invention
The invention aims to solve the problem that the temperature in the prior art affects the measurement result, and provides a fiber bragg grating acceleration sensor with a stepped cantilever beam and a measurement method thereof.
In order to achieve the above object, the technical solution of the present invention is: the fiber grating acceleration sensor comprises a fiber grating, two fiber gratings, an equal-thickness beam, a second-thickness beam, a base, a mass block and a stepped cantilever beam;
the top end and the bottom end of the base are respectively provided with a fiber guide groove and two fiber guide grooves;
The top end and the bottom end of the mass block are respectively provided with three fiber guide grooves and four fiber guide grooves;
the bottoms of the first fiber guide groove and the third fiber guide groove are positioned on the same horizontal plane, and the bottoms of the second fiber guide groove and the fourth fiber guide groove are positioned on the same horizontal plane;
The middle part of the side surface of the base is connected with a second-class thickness beam, the middle part of the side surface of the mass block is connected with a first-class thickness beam, and the second-class thickness beam is connected with the first-class thickness beam;
The equal-thickness beam and the equal-thickness beam form a stepped cantilever beam;
The two ends of the fiber bragg grating are respectively arranged in the fiber guiding groove and the two fiber guiding grooves, and the fiber bragg grating is positioned above the equal-thickness beam;
Two ends of the two fiber gratings are respectively arranged in the three fiber guide grooves and the four fiber guide grooves, and the two fiber gratings are positioned below the equal-thickness beam.
The widths of the first fiber guide groove, the second fiber guide groove, the third fiber guide groove and the fourth fiber guide groove are the same.
The three fiber guide grooves, the four fiber guide grooves and the stepped cantilever beam are arranged in parallel in space.
The thickness of the equal-thickness beam is the same as that of the equal-thickness beam, and the width of the equal-thickness beam is larger than that of the equal-thickness beam.
The first fiber grating and the second fiber grating are symmetrically arranged by taking the cross section of the ladder-type cantilever beam as the center.
The equal-thickness beam is a part of the connection of the stepped cantilever beam and the mass block, the equal-thickness beam is a part of the connection of the stepped cantilever beam and the base, and the base and the mass block are both quadrangular.
A measuring method of a fiber bragg grating acceleration sensor of a stepped cantilever beam comprises the following steps:
Step one, fixing a base of a sensor on the surface of a measured object;
step two, when the measured object vibrates, the vibration is transmitted to a fiber bragg grating and a fiber bragg grating on the sensor, and the form of the fiber bragg grating changes due to the vibration, so that the period of the grating and the effective refractive index of the grating change;
step three, firstly collecting the change data of the fiber grating, and then establishing a relation model between the acceleration of the measured object and the wavelength drift amount of the fiber grating according to the collected data;
and step four, obtaining a measurement result according to the relation model.
The relation model for establishing the acceleration of the measured object and the wavelength drift of the fiber bragg grating is specifically as follows:
When the sensor moves under the action of acceleration, the deflection of the movable end of the stepped cantilever beam is as follows:
Equation one:
Wherein: e is the elastic modulus of the stepped cantilever beam; i1 is the moment of inertia of a beam with the same thickness connected with the base; i2 is the moment of inertia of the equal thickness beam connected to the mass; the length of the equal-thickness beam connected with the base is a1, the width of the equal-thickness beam connected with the mass block is b1, the length of the equal-thickness beam connected with the mass block is a2, the width of the equal-thickness beam is b2, the thickness of the stepped cantilever beam is h, the distance from the fiber grating to the stepped cantilever beam is d, the mass of the mass block is m, and F is the force applied to the movable end of the cantilever beam;
the equivalent stiffness of the stepped cantilever beam is:
Formula II:
The deformation delta L of the free end of the cantilever beam is as follows:
And (3) a formula III:
The deformation Δl of the fiber grating is:
Equation four:
the axial strain epsilon of the fiber grating is as follows:
Formula five:
When the fiber grating is axially compressed or stretched, the relation between the wavelength drift amount delta lambda B of the fiber grating and the axial strain epsilon of the fiber grating is as follows:
Formula six: Δλ B＝(1-Pe)λB Δε
Wherein lambda B is the original wavelength of the fiber grating;
the sensitivity S of the sensor is:
formula seven:
The movable end of the stepped cantilever beam is the end of the stepped cantilever beam connected with the mass block.
Assuming that the external temperature is delta T, the wavelength drift amounts of the first fiber grating and the second fiber grating are as follows:
Formula eight:
formula nine:
Because the material of the first fiber grating and the material of the second fiber grating are the same, the parameters are similar and symmetrically stuck, when the mass block drives the cantilever beam to generate strain, the first fiber grating and the second fiber grating generate strain with the same size and opposite directions, so delta epsilon 1≈-Δε2＝Δε,ΔλB1≈ΔλB2＝ΔλB, and the formula eight and the formula nine are combined, so that the influence of temperature on the wavelength drift amount of the fiber gratings can be eliminated, and the following is obtained:
Formula ten:
the sensitivity of the sensor at this time is:
Formula eleven:
compared with the prior art, the invention has the beneficial effects that:
1. According to the fiber grating acceleration sensor of the ladder cantilever beam and the measuring method thereof, two ends of a fiber grating are respectively arranged in a fiber guiding groove and two fiber guiding grooves, the fiber grating is positioned above an equal-thickness beam, two ends of the two fiber gratings are respectively arranged in a three fiber guiding groove and a four fiber guiding groove, the two fiber gratings are positioned below the equal-thickness beam, and the double fiber gratings are arranged, so that the influence of temperature change on the central wavelength of the fiber is eliminated in a differential mode, and the sensitivity of the sensor is increased; the fiber grating is suspended, so that the fiber grating is prevented from contacting the cantilever beam, the chirp effect is prevented from being generated, and the measurement result is influenced; the prestress is applied when the fiber grating is installed, so that the fiber grating is prevented from being damaged when being stretched or compressed, and the service life of the sensor is prolonged. Therefore, the invention solves the problem that the temperature affects the measurement result, improves the service life of the sensor and ensures that the accuracy of the measurement result is higher.
2. According to the fiber bragg grating acceleration sensor of the stepped cantilever and the measuring method thereof, the middle part of the side face of the base is connected with the equal-thickness beam, the middle part of the side face of the mass block is connected with the equal-thickness beam, the equal-thickness beam and the equal-thickness beam form the stepped cantilever, the rigidity and the mass distribution state of the cantilever can be effectively changed by the stepped cantilever, higher sensitivity and natural frequency are obtained, the stepped cantilever is different from a conventional cantilever in structure, the rigidity and the mass distribution state of the stepped cantilever are different from those of the conventional cantilever, and under the same basic geometric dimension condition, the performance of the stepped cantilever sensor is more excellent than that of the conventional cantilever by redesigning parameters such as length, thickness and the like, and higher sensitivity and natural frequency are obtained. Therefore, the invention changes the rigidity and the mass distribution state of the cantilever beam, and improves the sensitivity and the natural frequency of the sensor.
Drawings
Fig. 1 is a schematic structural view of the present invention.
Fig. 2 is a front view of the structure of the present invention.
Fig. 3 is a top view of the structure of the present invention.
Fig. 4 is a left side view of the structure of the present invention.
Fig. 5 is a vibration state diagram of the present invention.
Fig. 6 is a flow chart of the present invention.
In the figure: the optical fiber grating comprises a first optical fiber guiding groove 1, a second optical fiber guiding groove 2, a third optical fiber guiding groove 3, a fourth optical fiber guiding groove 4, an optical fiber grating 5, a second optical fiber grating 6, an equal-thickness beam 7, an equal-thickness beam 8, a base 9, a mass block 10 and a stepped cantilever beam 11.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings and detailed description.
Referring to fig. 1 to 6, an optical fiber grating acceleration sensor of an echelon cantilever beam comprises an optical fiber grating 5, two optical fiber gratings 6, an equal-thickness beam 7, an equal-thickness beam 8, a base 9, a mass block 10 and an echelon cantilever beam 11;
the top end and the bottom end of the base 9 are respectively provided with a fiber guiding groove 1 and two fiber guiding grooves 2;
the top end and the bottom end of the mass block 10 are respectively provided with a three fiber guide groove 3 and a four fiber guide groove 4;
The bottoms of the first fiber guide groove 1 and the third fiber guide groove 3 are positioned on the same horizontal plane, and the bottoms of the second fiber guide groove 2 and the fourth fiber guide groove 4 are positioned on the same horizontal plane;
the middle part of the side surface of the base 9 is connected with a beam 8 with equal thickness, the middle part of the side surface of the mass block 10 is connected with a beam 7 with equal thickness, and the beam 8 with equal thickness is connected with the beam 7 with equal thickness;
the equal-thickness beam 7 and the equal-thickness beam 8 form a stepped cantilever beam 11;
Two ends of the fiber bragg grating 5 are respectively arranged in the fiber guiding groove 1 and the two fiber guiding grooves 2, and the fiber bragg grating 5 is positioned above the equal-thickness beam 7;
two ends of the two fiber gratings 6 are respectively arranged in the three fiber guiding grooves 3 and the four fiber guiding grooves 4, and the two fiber gratings 6 are positioned below the equal-thickness beam 7.
The widths of the first fiber guiding groove 1, the second fiber guiding groove 2, the third fiber guiding groove 3 and the fourth fiber guiding groove 4 are the same.
The three fiber guide grooves 1, the two fiber guide grooves 2 and the stepped cantilever beam 11 are arranged in parallel in space, and the three fiber guide grooves 3, the four fiber guide grooves 4 and the stepped cantilever beam 11 are arranged in parallel in space.
The thickness of the equal-thickness beam 7 is the same as that of the equal-thickness beam 8, and the width of the equal-thickness beam 7 is larger than that of the equal-thickness beam 8.
The first fiber bragg grating 5 and the second fiber bragg grating 6 are symmetrically arranged by taking the cross section of the stepped cantilever beam 11 as the center.
The equal-thickness beam 7 is a part of the stepped cantilever beam 11 connected with the mass block 10, the equal-thickness beam 8 is a part of the stepped cantilever beam 11 connected with the base 9, and the base 9 and the mass block 10 are both quadrangular.
A measuring method of a fiber bragg grating acceleration sensor of a stepped cantilever beam comprises the following steps:
step one, fixing a base 9 of a sensor on the surface of a measured object;
Step two, when the measured object vibrates, the vibration is transmitted to a fiber bragg grating 5 and a fiber bragg grating 6 on the sensor, and the form of the fiber bragg grating changes due to the vibration, so that the period of the grating and the effective refractive index of the grating change;
step three, firstly collecting the change data of the fiber grating, and then establishing a relation model between the acceleration of the measured object and the wavelength drift amount of the fiber grating according to the collected data;
and step four, obtaining a measurement result according to the relation model.
The relation model for establishing the acceleration of the measured object and the wavelength drift of the fiber bragg grating is specifically as follows:
when the sensor moves under the action of acceleration, the deflection of the movable end of the stepped cantilever beam 11 is as follows:
Equation one:
wherein: e is the elastic modulus of the step cantilever beam 11; i1 is the moment of inertia of the second-class thickness beam 8 connected to the base 9; i2 is the moment of inertia of the constant thickness beam 7 connected to the mass 10; the length of the equal-thickness beam 8 connected with the base 9 is a1, the width of the equal-thickness beam 8 is b1, the length of the equal-thickness beam 7 connected with the mass block 10 is a2, the width of the equal-thickness beam is b2, the thickness of the stepped cantilever beam 11 is h, the distance from the fiber grating to the stepped cantilever beam 11 is d, the mass of the mass block 10 is m, and F is the force applied to the movable end of the cantilever beam;
the equivalent stiffness of the stepped cantilever 11 is:
Formula II:
The deformation delta L of the free end of the cantilever beam is as follows:
And (3) a formula III:
The deformation Δl of the fiber grating is:
Equation four:
the axial strain epsilon of the fiber grating is as follows:
Formula five:
When the fiber grating is axially compressed or stretched, the relation between the wavelength drift amount delta lambda B of the fiber grating and the axial strain epsilon of the fiber grating is as follows:
Formula six: Δλ B＝(1-Pe)λB Δε
Grating period, namely the length from one refractive index change point to an adjacent refractive index change point, wherein the period and the effective refractive index of the grating affect the wavelength drift amount of the fiber grating;
Wherein lambda B is the original wavelength of the fiber grating;
the sensitivity S of the sensor is:
formula seven:
The movable end of the step-shaped cantilever beam 11 is the end of the step-shaped cantilever beam 11 connected with the mass block 10.
Assuming that the external temperature is Δt, the wavelength shift amounts of the first fiber grating 5 and the second fiber grating 6 are:
Formula eight:
formula nine:
Because the material of the first fiber bragg grating 5 and the second fiber bragg grating 6 are the same, the parameters are similar and symmetrically stuck, when the mass block 10 drives the cantilever beam to generate strain, the first fiber bragg grating 5 and the second fiber bragg grating 6 generate strain with the same size and opposite directions, so A epsilon 1≈-Δε2＝Δε,ΔλB1≈ΔλB2＝ΔλB is realized, and the influence of temperature on the wavelength drift amount of the fiber bragg gratings can be eliminated by combining the formula eight and the formula nine, so that the following is obtained:
Formula ten:
the sensitivity of the sensor at this time is:
Formula eleven:
example 1:
The fiber grating acceleration sensor of the ladder type cantilever beam comprises a fiber grating 5, two fiber gratings 6, an equal-thickness beam 7, an equal-thickness beam 8, a base 9, a mass block 10 and a ladder type cantilever beam 11; the top end and the bottom end of the base 9 are respectively provided with a fiber guiding groove 1 and two fiber guiding grooves 2; the top end and the bottom end of the mass block 10 are respectively provided with a three fiber guide groove 3 and a four fiber guide groove 4; the bottoms of the first fiber guide groove 1 and the third fiber guide groove 3 are positioned on the same horizontal plane, and the bottoms of the second fiber guide groove 2 and the fourth fiber guide groove 4 are positioned on the same horizontal plane; the middle part of the side surface of the base 9 is connected with a beam 8 with equal thickness, the middle part of the side surface of the mass block 10 is connected with a beam 7 with equal thickness, and the beam 8 with equal thickness is connected with the beam 7 with equal thickness; the equal-thickness beam 7 and the equal-thickness beam 8 form a stepped cantilever beam 11; two ends of the fiber bragg grating 5 are respectively arranged in the fiber guiding groove 1 and the two fiber guiding grooves 2, and the fiber bragg grating 5 is positioned above the equal-thickness beam 7; two ends of the two fiber gratings 6 are respectively arranged in the three fiber guiding grooves 3 and the four fiber guiding grooves 4, and the two fiber gratings 6 are positioned below the equal-thickness beam 7.
The measuring method of the fiber bragg grating acceleration sensor of the stepped cantilever comprises the following steps:
step one, fixing a base 9 of a sensor on the surface of a measured object;
Step two, when the measured object vibrates, the vibration is transmitted to a fiber bragg grating 5 and a fiber bragg grating 6 on the sensor, and the form of the fiber bragg grating changes due to the vibration, so that the period of the grating and the effective refractive index of the grating change;
step three, firstly collecting the change data of the fiber grating, and then establishing a relation model between the acceleration of the measured object and the wavelength drift amount of the fiber grating according to the collected data;
and step four, obtaining a measurement result according to the relation model.
Example 2:
example 2 is substantially the same as example 1 except that:
the relation model for establishing the acceleration of the measured object and the wavelength drift of the fiber bragg grating is specifically as follows:
when the sensor moves under the action of acceleration, the deflection of the movable end of the stepped cantilever beam 11 is as follows:
Equation one:
wherein: e is the elastic modulus of the step cantilever beam 11; i1 is the moment of inertia of the second-class thickness beam 8 connected to the base 9; i2 is the moment of inertia of the constant thickness beam 7 connected to the mass 10; the length of the equal-thickness beam 8 connected with the base 9 is a1, the width of the equal-thickness beam 8 is b1, the length of the equal-thickness beam 7 connected with the mass block 10 is a2, the width of the equal-thickness beam is b2, the thickness of the stepped cantilever beam 11 is h, the distance from the fiber grating to the stepped cantilever beam 11 is d, the mass of the mass block 10 is m, and F is the force applied to the movable end of the cantilever beam;
the equivalent stiffness of the stepped cantilever 11 is:
Formula II:
The deformation delta L of the free end of the cantilever beam is as follows:
And (3) a formula III:
The deformation Δl of the fiber grating is:
Equation four:
the axial strain epsilon of the fiber grating is as follows:
Formula five:
When the fiber grating is axially compressed or stretched, the relation between the wavelength drift amount delta lambda B of the fiber grating and the axial strain epsilon of the fiber grating is as follows:
Formula six: Δλ B＝(1-Pe)λB Δε
Wherein lambda B is the original wavelength of the fiber grating;
grating period: the length from one refractive index change point to the adjacent refractive index change point, the period and the effective refractive index of the grating all affect the wavelength drift amount of the fiber grating;
the sensitivity S of the sensor is:
formula seven:
The movable end of the step-shaped cantilever beam 11 is the end of the step-shaped cantilever beam 11 connected with the mass block 10.
Example 3:
Example 3 is substantially the same as example 2 except that:
In the measuring method of the fiber grating acceleration sensor of the ladder cantilever beam, if the external temperature is delta T, the wavelength drift amount of the first fiber grating 5 and the second fiber grating 6 is as follows:
Formula eight:
formula nine:
because the material of the first fiber bragg grating 5 and the second fiber bragg grating 6 are the same, the parameters are similar and symmetrically stuck, when the mass block drives the cantilever beam to generate strain, the first fiber bragg grating 5 and the second fiber bragg grating 6 generate strain with equal size and opposite directions, so delta epsilon 1≈-Δε2＝Δε,ΔλB1≈ΔλB2＝ΔλB, a formula eight and a formula nine are combined, the influence of temperature on the wavelength drift amount of the fiber bragg gratings can be eliminated, and the following formula is obtained:
Formula ten:
the sensitivity of the sensor at this time is:
Formula eleven:
Comparing formula seven with formula eleven, after temperature self-compensation is carried out through the double fiber grating, the influence of temperature on the wavelength is eliminated, wherein the front half part on the right side of the equal sign in formula eight and formula nine is the influence caused by strain, the rear half part is provided with the influence caused by temperature, the formula eight is subtracted by formula nine, the obtained formula ten does not contain T, the parameter representing temperature represents that the influence caused by temperature is eliminated, simultaneously, the sensitivity is doubled, the vibration signal detection of mechanical equipment can be realized, the double fiber grating can eliminate the influence of temperature change on the center wavelength of the fiber grating, the sensitivity of a sensor is increased, and the stiffness and the mass distribution state of the cantilever beam can be effectively changed by the stepped cantilever beam 11, so that higher sensitivity and natural frequency are obtained.
Example 4:
example 4 is substantially the same as example 1 except that:
The utility model provides a fiber grating acceleration sensor of ladder type cantilever beam, the width of a fiber guiding groove 1, two fiber guiding grooves 2, three fiber guiding grooves 3 and four fiber guiding grooves 4 is the same, be in space parallel arrangement each other between a fiber guiding groove 1, two fiber guiding grooves 2 and the ladder type cantilever beam 11 three, be in space parallel arrangement each other between three fiber guiding grooves 3, four fiber guiding grooves 4 and the ladder type cantilever beam 11 three for the atress is even when optic fibre is stretched or compressed, and the position when guaranteeing fiber grating installation is about the cantilever beam up-and-down symmetry, the calculation on the numerical value of being convenient for guarantees that fiber grating atress is even, reduces the error, the thickness of a thickness beam 7 is the same with the thickness of second class thickness beam 8, and the width of a thickness beam 7 is greater than the width of second class thickness beam 8, a fiber grating 5 and two fiber grating 6 use the cross section of ladder type cantilever beam 11 as central symmetry setting, when the calculation of eliminating the temperature influence is convenient for reduce other interference term factors, like fiber grating distance difference leads to the atress difference when being stretched or compressed for the optic fibre grating, produces the measuring result and is the equal to the cantilever beam, the quality is that a section 9 is the cantilever beam is connected with a base part 9, a section is the cantilever beam 9 and a base part is connected to a quality 9.
Example 5:
example 5 is substantially the same as example 4 except that:
The fiber grating acceleration sensor with the ladder cantilever beam is of an integrated structure, the manufacturing material is 304 stainless steel, the material mainly comprises iron, chromium and nickel, has good corrosion resistance and heat resistance, is suitable for most industrial environments, has density larger than that of a common steel structure, has larger mass under the condition of the same volume, has larger acting force under the same vibration amplitude, and has higher sensitivity.
Example 6:
Example 6 is substantially the same as example 4 except that:
An optical fiber grating acceleration sensor of an echelon cantilever applies a certain amount of prestress when fixing an optical fiber grating 5 and two optical fiber gratings 6; the application of a certain amount of prestressing force is specifically: placing the optical fiber on an adjustable workbench, wherein one end of the optical fiber is positioned on a fixed mounting plate through an optical fiber clamping mechanism, and the other end of the optical fiber is positioned on the fixed mounting plate through an optical fiber clamping mechanism, and fine-adjusting a translation stage after clamping the optical fiber, so that the optical fiber is subjected to certain tensile stress, and the application of prestress can be realized; when one fiber grating 5 is in a stretching state, two fiber gratings 6 are in a compressing state, when one fiber grating 5 is in a compressing state, two fiber gratings 6 are in a stretching state, when a measured object vibrates, the left fiber is compressed under the assumption that the mass block 10 of the sensor swings leftwards, the right fiber is stretched, and when the mass block 10 of the sensor swings rightwards, the right fiber is compressed, and the left fiber is stretched.
The above description is merely of preferred embodiments of the present invention, and the scope of the present invention is not limited to the above embodiments, but all equivalent modifications or variations according to the present disclosure will be within the scope of the claims.
Claims (10)
1. The fiber grating acceleration sensor of the ladder type cantilever beam is characterized by comprising a fiber grating (5), two fiber gratings (6), a beam with equal thickness (7), a beam with equal thickness (8), a base (9), a mass block (10) and the ladder type cantilever beam (11);
the top end and the bottom end of the base (9) are respectively provided with a fiber guide groove (1) and two fiber guide grooves (2);
The top end and the bottom end of the mass block (10) are respectively provided with three fiber guide grooves (3) and four fiber guide grooves (4);
The bottoms of the first fiber guide groove (1) and the third fiber guide groove (3) are positioned on the same horizontal plane, and the bottoms of the second fiber guide groove (2) and the fourth fiber guide groove (4) are positioned on the same horizontal plane;
The middle part of the side surface of the base (9) is connected with a beam (8) with equal thickness, the middle part of the side surface of the mass block (10) is connected with a beam (7) with equal thickness, and the beam (8) with equal thickness is connected with the beam (7) with equal thickness;
The equal-thickness beam (7) and the equal-thickness beam (8) form a stepped cantilever beam (11);
two ends of the fiber bragg grating (5) are respectively arranged in the fiber guiding groove (1) and the three fiber guiding grooves (3), and the fiber bragg grating (5) is positioned above the equal-thickness beam (7);
Two ends of the two fiber gratings (6) are respectively arranged in the two fiber guide grooves (2) and the four fiber guide grooves (4), and the two fiber gratings (6) are positioned below the equal-thickness beam (7);
The fiber bragg grating acceleration sensor of the stepped cantilever beam is measured according to the following method, and the measuring method comprises the following steps of:
Step one, fixing a base (9) of a sensor on the surface of a measured object;
step two, when the measured object vibrates, the vibration is transmitted to a fiber bragg grating (5) and two fiber bragg gratings (6) on the sensor, and the form of the fiber bragg gratings changes due to the vibration, so that the period of the gratings and the effective refractive index of the gratings change;
step three, firstly collecting the change data of the fiber grating, and then establishing a relation model between the acceleration of the measured object and the wavelength drift amount of the fiber grating according to the collected data;
Step four, obtaining a measurement result according to the relation model;
the relation model for establishing the acceleration of the measured object and the wavelength drift of the fiber bragg grating is specifically as follows:
When the sensor moves under the action of acceleration, the deflection of the movable end of the stepped cantilever beam (11) is as follows:
Equation one:
Wherein: e is the elastic modulus of the step-type cantilever beam (11); i1 is the moment of inertia of a second-class thickness beam (8) connected with the base (9); i2 is the moment of inertia of the constant-thickness beam (7) connected with the mass block (10); the length of the equal-thickness beam (8) connected with the base (9) is a1, the width of the equal-thickness beam is b1, the length of the equal-thickness beam (7) connected with the mass block (10) is a2, the width of the equal-thickness beam is b2, the thickness of the stepped cantilever beam (11) is h, the distance from the fiber grating to the stepped cantilever beam (11) is d, the mass of the mass block (10) is m, and F is the force applied to the movable end of the cantilever beam;
The equivalent stiffness of the stepped cantilever beam (11) is as follows:
Formula II:
The deformation delta L of the free end of the cantilever beam is as follows:
And (3) a formula III:
The deformation Δl of the fiber grating is:
Equation four:
the axial strain epsilon of the fiber grating is as follows:
Formula five:
When the fiber grating is axially compressed or stretched, the relation between the wavelength drift amount delta lambda B of the fiber grating and the axial strain epsilon of the fiber grating is as follows:
Formula six: Δλ B＝(1-Pe)λB Δε
Wherein lambda B is the original wavelength of the fiber grating;
the sensitivity S of the sensor is:
formula seven:
2. The fiber bragg grating acceleration sensor of the stepped cantilever according to claim 1, wherein: the widths of the first fiber guide groove (1), the second fiber guide groove (2), the third fiber guide groove (3) and the fourth fiber guide groove (4) are the same.
3. The fiber bragg grating acceleration sensor of the stepped cantilever according to claim 2, wherein: the two fiber guide grooves (2), the four fiber guide grooves (4) and the stepped cantilever beams (11) are arranged in parallel in space.
4. A fiber grating acceleration sensor of a stepped cantilever according to claim 1, 2 or 3, characterized in that: the thickness of the equal-thickness beam (7) is the same as that of the equal-thickness beam (8), and the width of the equal-thickness beam (7) is larger than that of the equal-thickness beam (8).
5. A fiber grating acceleration sensor of a stepped cantilever according to claim 1,2 or 3, characterized in that: the first fiber bragg grating (5) and the second fiber bragg grating (6) are symmetrically arranged by taking the cross section of the stepped cantilever beam (11) as the center.
6. A fiber grating acceleration sensor of a stepped cantilever according to claim 1,2 or 3, characterized in that: the equal-thickness beam (7) is a part of the stepped cantilever beam (11) connected with the mass block (10), the equal-thickness beam (8) is a part of the stepped cantilever beam (11) connected with the base (9), and the base (9) and the mass block (10) are both quadrangular.
7. A method for measuring an acceleration sensor of an optical fiber grating of a stepped cantilever according to claim 1, comprising the steps of:
Step one, fixing a base (9) of a sensor on the surface of a measured object;
step two, when the measured object vibrates, the vibration is transmitted to a fiber bragg grating (5) and two fiber bragg gratings (6) on the sensor, and the form of the fiber bragg gratings changes due to the vibration, so that the period of the gratings and the effective refractive index of the gratings change;
step three, firstly collecting the change data of the fiber grating, and then establishing a relation model between the acceleration of the measured object and the wavelength drift amount of the fiber grating according to the collected data;
and step four, obtaining a measurement result according to the relation model.
8. The fiber bragg grating acceleration sensor of the stepped cantilever according to claim 7, wherein: the relation model for establishing the acceleration of the measured object and the wavelength drift of the fiber bragg grating is specifically as follows:
When the sensor moves under the action of acceleration, the deflection of the movable end of the stepped cantilever beam (11) is as follows:
Equation one:
Wherein: e is the elastic modulus of the step-type cantilever beam (11); i1 is the moment of inertia of a second-class thickness beam (8) connected with the base (9); i2 is the moment of inertia of the constant-thickness beam (7) connected with the mass block (10); the length of the equal-thickness beam (8) connected with the base (9) is a1, the width of the equal-thickness beam is b1, the length of the equal-thickness beam (7) connected with the mass block (10) is a2, the width of the equal-thickness beam is b2, the thickness of the stepped cantilever beam (11) is h, the distance from the fiber grating to the stepped cantilever beam (11) is d, the mass of the mass block (10) is m, and F is the force applied to the movable end of the cantilever beam;
The equivalent stiffness of the stepped cantilever beam (11) is as follows:
Formula II:
The deformation delta L of the free end of the cantilever beam is as follows:
And (3) a formula III:
The deformation Δl of the fiber grating is:
Equation four:
the axial strain epsilon of the fiber grating is as follows:
Formula five:
When the fiber grating is axially compressed or stretched, the relation between the wavelength drift amount delta lambda B of the fiber grating and the axial strain epsilon of the fiber grating is as follows:
Formula six: Δλ B＝(1-Pe)λB Δε
Wherein lambda B is the original wavelength of the fiber grating;
the sensitivity S of the sensor is:
formula seven:
9. The fiber bragg grating acceleration sensor of the stepped cantilever according to claim 8, wherein: the movable end of the step-shaped cantilever beam (11) is the end of the step-shaped cantilever beam (11) connected with the mass block (10).
10. The fiber bragg grating acceleration sensor of the stepped cantilever according to claim 8, wherein: assuming that the external temperature is Δt, the wavelength drift amounts of the first fiber grating (5) and the second fiber grating (6) are:
Formula eight:
formula nine:
because the material of the optical fiber grating (5) and the material of the two optical fiber gratings (6) are the same, the parameters are similar and symmetrically stuck, when the mass block (10) drives the cantilever beam to generate strain, the optical fiber grating (5) and the two optical fiber gratings (6) generate strain with the same size and opposite directions, so delta epsilon 1≈-Δε2＝Δε,ΔλB1≈ΔλB2＝ΔλB is generated, and the influence of temperature on the wavelength drift amount of the optical fiber gratings can be eliminated by combining the formula eight and the formula nine, so that the following is obtained:
Formula ten:
the sensitivity of the sensor at this time is:
Formula eleven:
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