Fiber bragg grating vibration sensor adopting variable cross-section radial plate and wave spring

Abstract

A fiber bragg grating vibration sensor adopting a variable cross-section radial plate and wave springs comprises an upper pressing plate, an upper side wave spring, an upper fixing sleeve, an upper movable mass block, the variable cross-section radial plate, a lower movable mass block, a lower fixing sleeve, a lower side wave spring, a double-fiber bragg grating string and a lower pressing plate. The wave springs on the upper side and the lower side are compressed and positioned through the upper pressing plate, the lower pressing plate, the upper movable mass block and the lower movable mass block at the same time. The double-fiber grating string engraved with the double gratings connected in series is fixed in through holes of the upper pressing plate, the lower pressing plate, the upper movable mass block and the variable-cross-section radial plate in a straightened state. When the sensor is excited by the outside to generate a vibration signal, the mass block in the middle amplifies the vibration displacement through the variable cross-section radial plate, and simultaneously compresses and stretches the wave springs on the upper side and the lower side to drive the fiber bragg grating string packaged in the wave springs to feed back a bidirectional wavelength signal. Meanwhile, the influence of temperature drift can be eliminated through signals of the fully-differential double-sensing grating, the vibration pickup sensitivity is improved, and low-frequency excitation signals are effectively picked up.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the vibration monitoring technical field, concretely relates to a kind of fiber grating vibration sensor using variable cross-section radial plate and wave spring. BACKGROUND

[0002] In the field of vibration monitoring, vibration sensor converts mechanical vibration into measurable electrical signal, realizes the real-time monitoring and analysis of vibration frequency, amplitude, acceleration and other parameters, and is the core component of industrial equipment health management, structure safety evaluation and environmental monitoring.

[0003] Common vibration sensors include magneto-electric vibration sensor and fiber grating vibration sensor. Among them, magneto-electric vibration sensor has the following shortcomings: based on electromagnetic induction principle, output electrical signal is easy to be disturbed by external electromagnetic field; Performance changes significantly with temperature, and stability is not high; Sensitivity is limited by mechanical structure, measurement accuracy error is usually more than 1%, and nonlinear error increases with range edge; Effective frequency range is narrow, and it is difficult to capture low-frequency or high-frequency vibration signal; Complex structure, easy to wear after long-term use. Although existing fiber grating vibration sensor has the advantages of simple structure, high stability, high precision, wide dynamic range, anti-electromagnetic interference and simplifying field wiring compared with magneto-electric vibration sensor, it is difficult to ensure the pickup of ultra-low frequency vibration signal, and it is also necessary to further eliminate the influence of temperature drift and better improve the sensitivity.

[0004] Therefore, it is urgent to improve the existing fiber grating vibration sensor. UTILITY MODEL CONTENTS

[0005] To solve the above technical problems in the prior art, the utility model provides a kind of fiber grating vibration sensor using variable cross-section radial plate and wave spring, to better realize the pickup of ultra-low frequency vibration signal, improve sensitivity and realize temperature self-compensation function.

[0006] To solve the above technical problems, the utility model specifically uses the following technical solutions:

[0007] A kind of fiber grating vibration sensor using variable cross-section radial plate and wave spring, including: upper pressing plate, upper side wave spring, upper fixed sleeve, upper movable mass, variable cross-section radial plate, lower movable mass, lower fixed sleeve, lower side wave spring, double fiber grating string and lower pressing plate;

[0008] Upper fixed sleeve and lower fixed sleeve are coaxially stacked and fixedly arranged;

[0009] Upper pressing plate and lower pressing plate are respectively fixed at the upper end of upper fixed sleeve and the lower end of lower fixed sleeve;

[0010] The two ends of the upper wave spring are connected with the upper pressing plate and the upper movable mass respectively and are compressed and positioned;

[0011] The two ends of the lower wave spring are connected with the lower pressing plate and the lower movable mass respectively and are compressed and positioned;

[0012] The inner circle of the variable cross-section spoke is compressed by the upper movable mass and the lower movable mass which are fastened and connected;

[0013] The outer circle of the variable cross-section spoke is compressed by the upper fixed sleeve and the lower fixed sleeve which are fastened and connected;

[0014] The double fiber grating string comprises two series-connected packaged gratings, and is in a straightened state and is fixedly glued in the through hole penetrating through the upper pressing plate, the upper movable mass, the variable cross-section spoke, the lower movable mass and the lower pressing plate, and the two series-connected packaged gratings are located at the intermediate positions of the compressed upper and lower wave springs respectively; the two ends of the double fiber grating string are led out and connected to an external fiber grating demodulation device.

[0015] Preferably, the inner circle of the variable cross-section spoke has a first thickness, the outer circle of the variable cross-section spoke has a second thickness greater than the first thickness, and the thickness of the transition part of the variable cross-section spoke between the inner circle and the outer circle gradually increases along the direction from the inner circle to the outer circle.

[0016] Preferably, the lower surface of the upper pressing plate, the upper surface of the lower pressing plate, the upper surface of the upper movable mass and the lower surface of the lower movable mass are respectively provided with recessed groove seat rings; the recessed groove seat rings of the upper pressing plate and the upper movable mass are respectively embedded with the two sides of the upper wave spring, and the recessed groove seat rings of the lower pressing plate and the lower movable mass are respectively embedded with the two sides of the lower wave spring.

[0017] Preferably, the upper wave spring and the lower wave spring are composed of a plurality of thin sheet ring-shaped elastic metal elements with a rhombic longitudinal section; each thin sheet ring-shaped elastic metal element is composed of a plurality of wave crests and troughs connected end to end; the two sides of the upper wave spring and the lower wave spring are respectively embedded with the corresponding recessed groove seat rings in a surface contact manner.

[0018] Preferably, the upper pressing plate and the lower pressing plate are respectively fixed in the threaded holes of the upper fixed sleeve and the lower fixed sleeve by fixed screws.

[0019] Preferably, the upper movable mass and the lower movable mass are fastened and connected by an inner hexagonal stud, a gasket and a nut, and the upper wave spring and the lower wave spring are also fastened and connected by an inner hexagonal stud, a gasket and a nut.

[0020] Preferably, the upper cover plate, the outer shell and the lower cover plate are further included; wherein the upper pressing plate, the upper side wave spring, the upper fixed sleeve, the upper movable mass, the variable cross-section web, the lower movable mass, the lower fixed sleeve, the lower side wave spring, the double fiber grating string and the lower pressing plate are all accommodated inside the cylindrical outer shell; the lower fixed sleeve is horizontally fixed inside the outer shell; the upper cover plate and the lower cover plate cover the upper and lower openings of the outer shell respectively by screwing screws into the upper and lower threaded holes of the outer shell, and realize fastening connection with the outer shell.

[0021] Preferably, the lower cover plate is processed with a mounting threaded hole, which is used for fixing the fiber grating vibration sensor adopting the variable cross-section web and the wave spring to a vibration measurement installation surface through an adapter screw.

[0022] Preferably, two sealing ends arranged on the side wall of the outer shell and two armored optical cables connected with the two sealing ends respectively are further included; wherein the bare fibers at the two ends of the double fiber grating string respectively pass through two different threaded holes on the side wall of the outer shell into the corresponding sealing ends and armored optical cables.

[0023] Preferably, the upper movable mass and the lower movable mass are made of hard alloy material, and the density is preferably 14-16 g / cm 3 .

[0024] The fiber grating vibration sensor adopting the variable cross-section web and the wave spring structure of the utility model can achieve the following technical effects:

[0025] 1. The fiber grating vibration sensor adopting the variable cross-section web and the wave spring structure of the utility model selects appropriate structure size and elastic coefficient mode through parameterized design of the wave spring to improve the vibration pickup sensitivity, and amplifies the vibration displacement through the variable cross-section web, realizes pickup of the ultra-low frequency vibration signal, and the vibration pickup sensitivity can reach about 800pm / g, and the lowest vibration pickup frequency reaches 0.5Hz.

[0026] 2. The utility model discloses a wave spring, a variable cross-section web and a movable mass that are symmetrically compressed on both sides to form a vibration response system, and there is no other associated component between the elastic sensitive components, so that the redundant error is reduced, and the output stability of the sensor is improved. Through the structure design, the wave spring elastic component is in a reasonable compression amount, so that the movable mass and the optical fiber have an elastic buffer area, so that the movable mass can have a larger vibration displacement in the axial direction when being subjected to external excitation, and at the same time, the sensor is guaranteed not to break the optical fiber when being subjected to a larger vibration impact, and the reliability of the sensor is improved.

[0027] 3.The utility model discloses a temperature compensation self-compensation is realized through double grating structure, and because the double grating of the same optical fiber is written symmetrically and is packaged, the vibration strain of the outside world is just opposite and equal amplitude, and the temperature environment of two packaging gratings is same, therefore can eliminate the influence of temperature drift through the signal matching of double sensing grating (the difference of demodulation symmetric grating wavelength signal) and improve the sensitivity multiplication, can effectively improve the low frequency vibration pickup ability of sensor. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a structure schematic diagram of the optical fiber grating vibration sensor of the utility model adopting variable cross section web and wave spring;

[0029] Fig. 2 (a) is the side view of the basic unit of the wave spring adopted by the utility model;

[0030] Fig. 2 (b) is the top view of the basic unit of the wave spring adopted by the utility model;

[0031] Fig. 2 (c) is the half-wave force diagram of the basic unit of the wave spring adopted by the utility model;

[0032] Figure 3 It is the structure schematic diagram of the variable cross section web adopted by the utility model.

[0033] Mark explanation:

[0034] 01 - upper cover plate, 02 - shell, 03 - upper pressing plate, 04 - fixed screw, 05 - upper side wave spring, 06 - upper fixed sleeve, 07 - upper movable mass, 08 - nut, 09 - gasket, 10 - variable cross section web, 101 - inner ring, 102 - outer ring, 11 - inner hexagonal stud, 12 - lower movable mass, 13 - lower fixed sleeve, 14 - lower side wave spring, 15 - double fiber grating string, 16 - lower pressing plate, 17 - lower cover plate, 18 - end seal, 19 - armored cable DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantage of the utility model more clear, the technical scheme of the utility model will be clearly and completely described below in combination with the drawings in the embodiment of the utility model. The embodiment described in the application is only a part of the embodiment of the utility model, not all embodiments. Based on the spirit of the utility model, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the utility model.

[0036] As Figure 1As shown in one embodiment, the utility model provides a kind of fiber grating vibration sensor using variable cross-section spoke and wave spring, including: upper pressing plate 03, upper wave spring 05, upper fixed sleeve 06, upper movable mass 07, variable cross-section spoke 10, lower movable mass 12, lower fixed sleeve 13, lower wave spring 14, double fiber grating string 15 and lower pressing plate 16.

[0037] As Figure 1 As shown, wherein, upper fixed sleeve 06 and lower fixed sleeve 13 are coaxially stacked and fixedly arranged.Upper pressing plate 03 and lower pressing plate 16 are fixed at the upper end of upper fixed sleeve 06 and the lower end of lower fixed sleeve 13 respectively.The two ends of upper wave spring 05 are connected with upper pressing plate 03 and upper movable mass 07 respectively and are compressed and positioned, and the two ends of lower wave spring 14 are connected with lower pressing plate 16 and lower movable mass 12 respectively and are compressed and positioned.The inner ring of variable cross-section spoke 10 is compressed by upper movable mass 07 and lower movable mass 12 connected tightly, and the outer ring of variable cross-section spoke 10 is compressed by upper fixed sleeve 06 and lower fixed sleeve 13 connected tightly.Double fiber grating string 15 includes two series encapsulated gratings, and passes through and is fixedly glued in the through hole passing through upper pressing plate 03, upper movable mass 07, variable cross-section spoke 10, lower movable mass 12 and lower pressing plate 16 in straightened state.The two series encapsulated gratings are located at the middle position of compressed upper wave spring 05 and lower wave spring 14 respectively.The two ends of double fiber grating string 15 are led out and connected to external fiber grating demodulation equipment.

[0038] In the embodiment, the wave spring compressed and distributed symmetrically on the upper and lower sides, the variable cross-section spoke and the upper and lower movable masses form a vibration response system to pick up external excitation, and double gratings are used as vibration sensing sensitive elements.When the vibration response system is subjected to external excitation acceleration along the vertical direction of the axial direction, the variable cross-section spoke drives the upper and lower movable masses to be subjected to inertia effect and respectively applies tensile and compressive force to the wave spring in the compressed state, so that the upper and lower wave springs are elongated and compressed in the axial direction, and at this time, the upper and lower encapsulated grating strings are also stretched and compressed, so that the strain amount is opposite, and the grating wavelength drift amount is opposite, the vibration sensitivity is doubled, so that the external excitation signal is converted into the wavelength modulation signal of the fiber grating, and finally connected to the fiber grating demodulation equipment to collect and demodulate the vibration wavelength signal.Meanwhile, the variable cross-section spoke 10 can amplify the vibration displacement, realize the pickup of ultralow frequency vibration signal, and greatly improve the vibration pickup sensitivity.In addition, the double gratings encapsulated symmetrically by the same fiber have opposite and equal amplitude vibration strain, and the two encapsulated gratings are subjected to the same temperature environment, so that the influence of temperature drift can be eliminated (the difference between the wavelength signals of the symmetric gratings is demodulated) and the sensitivity is doubled through the signal matching of the double sensing gratings, which can effectively improve the low frequency vibration pickup capability of the sensor.

[0039] In a further preferred embodiment, as shown in Figure 3 The inner circle 101 of the variable cross-section spoke 10 has a first thickness, the outer circle 102 of the variable cross-section spoke 10 has a second thickness greater than the first thickness, and the thickness of the transition portion between the inner circle 101 and the outer circle 102 of the variable cross-section spoke 10 gradually increases in the direction from the inner circle to the outer circle. In this way, the vibration of the upper movable mass 07 and the lower movable mass 12 in the axial direction can be better ensured, and the lateral vibration deviation can be reduced.

[0040] In a further preferred embodiment, the lower surface of the upper pressing plate 03, the upper surface of the lower pressing plate 16, the upper surface of the upper movable mass 07, and the lower surface of the lower movable mass 12 are respectively provided with concave groove seats. The concave groove seats of the upper pressing plate 03 and the upper movable mass 07 are respectively embedded with the two sides of the upper wave spring 05, and the concave groove seats of the lower pressing plate 16 and the lower movable mass 12 are respectively embedded with the two sides of the lower wave spring 14. In this way, the upper wave spring 05 and the lower wave spring 14 can be detachably connected with the upper and lower pressing plates and the upper and lower movable masses, and the installation and disassembly process is convenient. At the same time, it can also effectively avoid the lateral displacement of the upper and lower wave springs and the upper and lower pressing plates and the upper and lower movable masses.

[0041] In a further preferred embodiment, the upper pressing plate 03 and the lower pressing plate 16 are fixed in the threaded holes of the upper fixed sleeve 06 and the lower fixed sleeve 13 respectively by the fixing screws 04 to realize fastening and detachable connection.

[0042] In a further preferred embodiment, the upper movable mass 07 and the lower movable mass 12 are fastened and connected by the inner hexagonal stud 11, the gasket 09 and the nut 08, and the upper wave spring 05 and the lower wave spring 14 are also fastened and connected by the inner hexagonal stud 11, the gasket 09 and the nut 08, so as to realize the pressing of the inner circle of the variable cross-section spoke 10 between the upper movable mass 07 and the lower movable mass 12, and the pressing of the outer circle of the variable cross-section spoke 10 between the upper fixed sleeve 06 and the lower fixed sleeve 13.

[0043] In a further preferred embodiment, the fiber grating vibration sensor of the utility model further comprises an upper cover plate 01, a shell 02 and a lower cover plate 17. Among them, the upper pressing plate 03, the upper side wave spring 05, the upper fixed sleeve 06, the upper movable mass 07, the variable cross-section spoke 10, the lower movable mass 12, the lower fixed sleeve 13, the lower side wave spring 14, the double fiber grating string 15 and the lower pressing plate 16 are all accommodated in the inside of the cylindrical shell 02. The lower fixed sleeve 13 is horizontally fixed in the shell 02. The upper cover plate 01 and the lower cover plate 17 cover the upper and lower openings of the shell 02 respectively by screwing the screws into the upper and lower threaded holes of the shell 02 and realize the fastening connection with the shell 02. By setting the upper cover plate 01, the shell 02 and the lower cover plate 17, the internal vibration response system can be better protected from the outside, other than the measured vibration, to reduce the wear of the internal vibration response system and provide a stable test environment for it.

[0044] In a further preferred embodiment, the lower cover plate 17 is processed with a mounting threaded hole, which is used to fix the fiber grating vibration sensor on the vibration measuring installation surface by adapter screws.

[0045] In a further preferred embodiment, the fiber grating vibration sensor of the utility model further comprises two sealing ends 18 arranged on the side wall of the shell 02 and two armored optical cables 19 connected with the two sealing ends 18 respectively. Among them, the bare fibers at both ends of the double fiber grating string 15 respectively pass through two different threaded holes on the side wall of the shell 02 into the corresponding sealing ends 18 and armored optical cables 19. By setting the sealing ends 18 and armored optical cables 19, the electromagnetic interference suffered by the vibration signals transmitted in the double fiber grating string 15 can be better shielded, thereby improving the signal sensitivity.

[0046] As shown in FIG. 2 (a)~2 (b), the upper side wave spring 05 and the lower side wave spring 14 adopted by the utility model are rhombic sheet ring elastic metal elements composed of a plurality of wave peaks and troughs, and the upper side wave spring 05 and the lower side wave spring 14 can respectively adopt the face contact mode with the concave groove seat ring of the upper pressing plate 03, the upper movable mass 07 and the lower movable mass 12, the lower pressing plate 16, so that the wave spring contact is more uniform, the axial pressure can be borne, and a relatively accurate elastic ratio can be provided. The stiffness coefficient K of the wave spring has a direct impact on the sensitivity S and the natural resonance frequency f0 of the vibration sensor, and the elastic coefficient K of the wave spring is mainly determined by the material elastic modulus E, the cross-sectional moment of inertia I, the matching shaft diameter (inner diameter) Dn, the matching hole diameter (outer diameter) Dw, the wire diameter d, the wave number N, the free height H and the working height h. The wave spring structure is in the form of alternating wave peaks and troughs along the circumferential direction, and when the deformation relationship caused by the load change of the wave spring is researched, a wavelength basic unit can be intercepted for calculation by referring to the bending beam model. f 0 have direct influence, its elastic coefficient K is mainly decided by its material elastic modulus E, cross-sectional moment of inertia I, matching shaft diameter (inner diameter) Dn, matching hole diameter (outer diameter) Dw, wire diameter d, wave number N, free height H and working height h. The wave spring structure is in the form of alternating wave peaks and troughs along the circumferential direction, and when the deformation relationship caused by the load change of the wave spring is researched, a wavelength basic unit can be intercepted for calculation by referring to the bending beam model.

[0047] Because of the structural characteristics of the wave spring, if the wave spring is subjected to a P load, the wave peak position is the main load bearing part and the stress is uniform, then the load on each wave peak is F = P / N (ignoring the diameter and thickness of the wave spring), and N is the number of wave peaks in the diamond sheet ring-shaped elastic metal element.

[0048] Figure 2(c) is a half-wave force diagram corresponding to the wave peak position in the basic unit of the wave spring. In combination with Figure 2(c), the static equilibrium equation is

[0049] (1)

[0050] (2)

[0051] The support reaction force is obtained as:

[0052] (3)

[0053] wherein, M A is the bending moment about the pivot point A, M B is the bending moment about the pivot point B; F RA is the reaction force at the pivot point A, F RB is the reaction force at the pivot point B, a is the distance from the pivot point A to the midpoint C, and b is the distance from the pivot point B to the midpoint C, L is the diameter of the wave spring.

[0054] In the half-wave force diagram, the bending moments of the AC segment and the CB segment are M 1 and M 2 respectively:

[0055] (4)

[0056] (5)

[0057] wherein x1 is the distance from the AC segment of the wave spring to the pivot point A, and x2 is the distance from the CB segment of the wave spring to the pivot point A.

[0058] The wave spring satisfies the deflection continuity condition, and at any point of the wave spring, there is a unique deflection and rotation angle, so the rotation angles and deflections of the intersection sections of the two end surfaces of the AC segment and the CB segment are equal. Substituting equations (4) and (5) into the rotation angle and deflection quadrature formula, the rotation angles and deflections of the AC segment and the CB segment are obtained as:

[0059] For the AC segment, the rotation angle equation and the deflection equation are respectively:

[0060] (6)

[0061] (7)

[0062] For CB segment, the rotation angle equation and deflection equation are respectively:

[0063] (8)

[0064] (9)

[0065] Wherein, and are the rotation angles of AC segment and CB segment respectively, and are the deflections of AC segment and CB segment respectively.

[0066] When the wave spring is loaded, the stress is mainly concentrated in the wave crest and wave trough positions, that is, the midpoint of the half wave in the simply supported beam model, that is, a=b=L / 2, at this time, x1=x2=L / 2, substitute into the above deflection equation, that is, equations (6)-(9), the expression of the half wave load deformation ω of the wave spring can be obtained:

[0067] (10)

[0068] The deformation of a complete wave under the action of load P is twice the deformation of the half wave, that is, the deflection of a complete wave Expression:

[0069] (11)

[0070] For a circular cross-section wave spring, the total wave length is πDS, so the half wave length of the circular cross-section wave spring is L=πDS / 2N. Substitute the elastic modulus of the wave spring and the moment of inertia I=πd4 / 64 into equation (11) to obtain:

[0071] (12)

[0072] Then the stiffness of the wave spring K is:

[0073] (13)

[0074] According to the definition of the sensitivity of the acceleration sensor, the sensitivity S of the sensor is the ratio of the change amount of the center wavelength of the fiber grating to the acceleration a, that is: S=Δλ / a, wherein Δλ is the change amount of the center wavelength of the sensing grating under strain, λ B is the initial wavelength of the sensing grating, which can be expressed as:

[0075] (14)

[0076] wherein P e is the effective photoelastic coefficient related to the photoelastic effect of the fiber; δ αx is the strain of the fiber grating along the axial direction. Substituting formula (13), δ αx =F / K and F=ma into S=Δλ / a, the expression of the sensitivity of the sensor single-side strain grating is obtained S 1:

[0077] (15)

[0078] According to the structural natural frequency formula, the resonance frequency of the sensor is obtained f 0:

[0079] (16)

[0080] Therefore, in a further preferred embodiment, the upper movable mass 07 and the lower movable mass 12 are selected from hard alloy materials, and the density is preferably 14-16 g / cm 3 , preferably 14.7 g / cm 3 , which is heavier than the material of other parts. As can be seen from formula (15), the heavier the vibrating mass, the higher the sensitivity of the sensor.

[0081] In addition, in a further preferred embodiment, the double fiber grating string 15 of the fiber grating vibration sensor of the utility model adopts a light-sensitive element, and needs to be clamped on a displacement clamp to apply a certain tension during packaging, so as to ensure that the double fiber grating string 15 passes through and is glued in the through hole of the upper pressing plate 03, the lower pressing plate 16, the upper movable mass 07, the variable cross-section radial plate 10 and the lower movable mass 12 in a straight state, and the two packaged gratings in series are respectively located at the middle position of the two sides of the compressed wave spring. Among them, the two packaged gratings in series are preferably Bragg gratings, which can be respectively denoted as FBG1 and FBG2. When the sensor receives external excitation to produce vibration, the center wavelength changes of FBG1 and FBG2 are respectively:

[0082] (17)

[0083] (18)

[0084] In formula (17), (18), , , , respectively, the center wavelength change and the center wavelength of FBGl and FBG2; P eis the photoelastic coefficient; and α1 and α2 are thermal expansion coefficients of FBGl and FBG2 respectively; ξ 1 and ξ 2 are thermal-optical coefficients of FBGl and FBG2 respectively; T is a temperature change value; ε 1 and ε 2 are strain values of FBGl and FBG2 respectively.

[0085] Since the two Bragg gratings have the same temperature sensitivity coefficient, when the elastic body vibrates up and down, the strain values of the two gratings are equal in size and opposite in direction, that is, ε 1=- ε 2= ε , formula (9) minus formula (10) can be obtained:

[0086] (19)

[0087] According to the vibration acceleration sensitivity formula S=Δλ / a, the wavelength difference of the double fiber grating string is twice that of the single fiber grating, so the sensitivity of the vibration sensor using the double fiber grating string will be doubled, and the influence of the external temperature on the measurement result can be compensated.

[0088] Experiments prove that the optical fiber grating vibration sensor adopting the variable cross-section web plate and the wave spring structure can achieve the following technical effects:

[0089] 1. The optical fiber grating vibration sensor adopting the variable cross-section web plate and the wave spring structure of the utility model selects appropriate structure size and elastic coefficient mode through parameterized design of the wave spring to improve the vibration pickup sensitivity, and amplifies the vibration displacement through the variable cross-section web plate, realizes the pickup of the ultra-low frequency vibration signal, and the vibration pickup sensitivity can reach about 800pm / g, and the lowest vibration pickup frequency reaches 0.5Hz.

[0090] 2. The utility model comprises a vibration response system composed of the wave spring, the variable cross-section web plate and the movable mass block distributed symmetrically on both sides, and there is no other associated component between the elastic sensitive components, so that the redundant error is reduced, and the output stability of the sensor is improved. Through the structure design, the wave spring elastic component is in a reasonable compression amount, so that the elastic buffer area exists between the movable mass block and the optical fiber, so that the movable mass block can have a larger vibration displacement in the axial direction when being subjected to external excitation, and meanwhile, the sensor is prevented from being broken when being subjected to a larger vibration impact, and the reliability of the sensor is improved.

[0091] 3.The utility model discloses a temperature compensation self-compensation is realized through double grating structure, because the double grating of same optical fiber engraves and writes symmetric package, the vibration strain variable of response outside is just opposite and the same, and the temperature environment of two package gratings is same, therefore can eliminate the influence of temperature drift through the signal matching of double sensing grating (the difference of demodulation symmetric grating wavelength signal) and improve the sensitivity multiplication, can effectively improve the low frequency pick -up ability of sensor.

[0092] Finally, it should be noted that the above examples are used to illustrate the technical solutions of the present application, but not to limit it. Although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced, without departing from the spirit and scope of the present application. Any modification or equivalent replacement that does not depart from the spirit and scope of the present application should be covered by the protection scope of the claims of the present application.

Claims

1. A fiber optic grating vibration sensor employing a variable cross-section web and a wave spring, characterized by, include: Upper pressure plate, upper wave spring, upper fixed sleeve, upper movable mass block, variable cross-section spoke, lower movable mass block, lower fixed sleeve, lower wave spring, dual fiber grating string and lower pressure plate; The upper fixed sleeve and the lower fixed sleeve are coaxially stacked and fixed; The upper pressing plate and the lower pressing plate are fixed to the upper end of the upper fixing sleeve and the lower end of the lower fixing sleeve respectively; The two ends of the upper wave spring are respectively connected to the upper pressure plate and the upper movable mass block and are compressed and positioned; The two ends of the lower wave spring are respectively connected to the lower pressure plate and the lower movable mass block and are compressed and positioned; the upper wave spring and the lower wave spring are composed of multiple thin-sheet annular elastic metal elements with diamond-shaped longitudinal sections; each thin-sheet annular elastic metal element is composed of multiple wave crests and troughs connected end to end; The inner ring of the variable-section spoke is pressed by an upper movable mass block and a lower movable mass block that are tightly connected; The outer ring of the variable-section spoke is pressed by the upper and lower fixed sleeves that are tightly connected; The dual-FBG string includes two packaged gratings connected in series, which are passed through and glued into the through-holes that penetrate the upper pressure plate, the upper movable mass block, the variable-section spoke plate, the lower movable mass block, and the lower pressure plate in a stretched state. The two packaged gratings in series are respectively located between the compressed upper and lower wave springs. The two ends of the dual-FBG string are respectively led out and connected to the external FBG demodulation equipment. Resonant frequency of a sensor f 0 is: wherein, E Dn, Dw, d and N are the material elastic modulus, the mating shaft diameter, the mating hole diameter, the wire diameter, and the wave number of the upper wave spring or the lower wave spring, respectively.

2. A fiber Bragg grating vibration sensor employing a variable cross-section web and a wave spring as claimed in claim 1, wherein, The inner ring of the variable-section web has a first thickness, the outer ring of the variable-section web has a second thickness greater than the first thickness, and the thickness of the transition portion between the inner ring and the outer ring of the variable-section web gradually increases from the inner ring to the outer ring.

3. A fiber Bragg grating vibration sensor employing a variable cross-section web and a wave spring as claimed in claim 1, wherein, The lower surface of the upper pressure plate, the upper surface of the lower pressure plate, the upper surface of the upper movable mass block and the lower surface of the lower movable mass block are respectively provided with concave groove seat rings; wherein, the concave groove seat rings of the upper pressure plate and the upper movable mass block are respectively engaged with the two sides of the upper wave spring, and the concave groove seat rings of the lower pressure plate and the lower movable mass block are respectively engaged with the two sides of the lower wave spring.

4. A fiber Bragg grating vibration sensor employing a variable cross-section web and a wave spring as claimed in claim 3, wherein, Both sides of the upper wave spring and the lower wave spring are respectively engaged with the corresponding concave groove seat rings in a surface contact manner.

5. A fiber Bragg grating vibration sensor employing a variable cross-section web and a wave spring as recited in claim 1, wherein, The upper pressing plate and the lower pressing plate are respectively fixed in the threaded holes of the upper fixing sleeve and the lower fixing sleeve by fixing screws.

6. A fiber Bragg grating vibration sensor employing a variable cross-section web and a wave spring as recited in claim 1, wherein, The upper movable mass block and the lower movable mass block are fastened and connected by means of hexagon socket studs, washers and nuts, and the upper wave spring and the lower wave spring are also fastened and connected by means of hexagon socket studs, washers and nuts.

7. A fiber Bragg grating vibration sensor employing a variable cross-section web and a wave spring as in claim 1, wherein, It also includes an upper cover plate, an outer shell and a lower cover plate; wherein, the upper pressure plate, the upper wave spring, the upper fixed sleeve, the upper movable mass block, the variable-section spoke plate, the lower movable mass block, the lower fixed sleeve, the lower wave spring, the dual fiber optic grating string and the lower pressure plate are all accommodated inside the cylindrical outer shell; the lower fixed sleeve is horizontally fixed in the outer shell; the upper cover plate and the lower cover plate respectively cover the upper and lower openings of the outer shell by screwing screws into the upper and lower threaded holes of the outer shell, and realize a fastening connection with the outer shell.

8. A fiber Bragg grating vibration sensor employing a variable cross-section web and a wave spring as claimed in claim 7, wherein, The lower cover plate is processed with a mounting threaded hole, and the mounting threaded hole is used to fix the fiber optic Bragg grating vibration sensor using a variable-section spoke plate and a wave spring on a vibration measurement mounting surface through an adapter screw.

9. A fiber Bragg grating vibration sensor employing a variable cross-section web and a wave spring as in claim 7, wherein, The application also discloses a double fiber grating sensing system, which comprises a double fiber grating sensing head and a double fiber grating sensing system. The bare fibers at two ends of the double fiber grating are respectively threaded into corresponding sealing ends and armored optical cables through two different threaded holes on the side wall of the shell.

10. A fiber Bragg grating vibration sensor employing a variable cross-section web and a wave spring as recited in claim 1, wherein, The upper movable mass and the lower movable mass are made of hard alloy material with a density of 14-16 g / cm 3 .

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