FBG acceleration sensor based on bearing and flexible hinge and measurement method

Abstract

The present application is applicable to the technical field of acceleration sensors, and provides a FBG acceleration sensor based on bearings and flexible hinges and a measurement method, wherein the FBG acceleration sensor comprises: a first mass block, a second mass block, a flexible hinge, a first bearing seat, a second bearing seat and a fiber grating; the first mass block and the second mass block are arranged parallel to each other, and the flexible hinge is connected between the two mass blocks; the first bearing seat and the second bearing seat are respectively arranged on the outer side surfaces of the first mass block and the second mass block; the fiber grating comprises a first fiber grating and / or a second fiber grating, the first fiber grating is arranged between the upper ends of the two mass blocks, and / or the second fiber grating is arranged between the lower ends of the two mass blocks. The FBG acceleration sensor based on bearings and flexible hinges provided in the present application has high sensitivity, high linearity and high natural frequency, and can realize accurate measurement of medium and high frequency vibration signals.

Description

Technical Field

[0001] The present application relates to the technical field of acceleration sensors, and in particular to an FBG acceleration sensor based on a bearing and a flexible hinge and a measurement method. Background Art

[0002] The accurate measurement of medium and high frequency vibration signals (i.e., the vibration acceleration of medium and high frequency vibration signals) is of great significance for many engineering fields, such as high-speed EMU axle box vibration monitoring and microseismic monitoring. Traditional electrical sensors have the disadvantages of being susceptible to electromagnetic interference, signal attenuation caused by long wires, and difficulty in application in special environments. Fiber Bragg Grating (FBG in English and FBG in Chinese) acceleration sensors use passive sensing elements. The optical signal transmission is not affected by electromagnetic and distance factors. They are corrosion-resistant, networkable, and easy to implement distributed sensing. They are suitable for vibration monitoring in harsh environments, and have attracted widespread attention from scientific researchers.

[0003] However, existing FBG accelerometers have problems such as low sensitivity, low linearity and low natural frequency, and are unable to achieve accurate measurement of medium and high frequency vibration signals. Summary of the invention

[0004] In view of this, the embodiments of the present application provide a FBG acceleration sensor and a measurement method based on bearings and flexible hinges to solve the technical problem that existing acceleration sensors cannot achieve accurate measurement of medium and high frequency vibration signals.

[0005] In a first aspect, an embodiment of the present application provides an FBG acceleration sensor based on a bearing and a flexible hinge, comprising: a first mass block, a second mass block, a flexible hinge, a first bearing seat, a second bearing seat and a fiber grating.

[0006] The first mass block and the second mass block are arranged parallel to each other, and the side surfaces of the first mass block and the second mass block close to each other are the inner side surfaces; the first end of the flexible hinge is connected to the inner side surface of the first mass block, and the second end of the flexible hinge is connected to the inner side surface of the second mass block.

[0007] The first end of the first bearing seat is connected to the center position of the outer side surface of the first mass block, and the first end of the second bearing seat is connected to the center position of the outer side surface of the second mass block; the first bearing seat and the second bearing seat are respectively provided with a first bearing hole and a second bearing hole, and the axial direction of the bearing hole is perpendicular to the axial direction of the mass block; the side opposite to the inner side surface of the mass block is the outer side surface of the mass block.

[0008] The fiber grating includes a first fiber grating and / or a second fiber grating; the first fiber grating is arranged between the upper end of the first mass block and the upper end of the second mass block, and / or the second fiber grating is arranged between the lower end of the first mass block and the lower end of the second mass block.

[0009] In a possible implementation manner of the first aspect, the FBG acceleration sensor based on the bearing and the flexible hinge further includes: a first extension rod, a second extension rod, a third extension rod and a fourth extension rod.

[0010] The first extension rod and the second extension rod are respectively arranged on the upper and lower surfaces of the first mass block, and are extended along the axial direction of the first mass block; the third extension rod and the fourth extension rod are respectively arranged on the upper and lower surfaces of the second mass block, and are extended along the axial direction of the second mass block. The first fiber grating is arranged between the free end of the first extension rod and the free end of the third extension rod, and / or the second fiber grating is arranged between the free end of the second extension rod and the free end of the fourth extension rod.

[0011] In a possible implementation of the first aspect, the FBG acceleration sensor based on bearings and flexible hinges also includes: a shell, a third bearing seat and a fourth bearing seat; the third bearing seat and the fourth bearing seat are respectively arranged at the center position of the left and right inner sides of the shell; the third bearing seat and the fourth bearing seat are respectively provided with a third bearing hole and a fourth bearing hole, and the axial direction of the bearing hole is perpendicular to the axial direction of the shell.

[0012] In a possible implementation of the first aspect, the FBG acceleration sensor based on bearings and flexible hinges also includes: a first bearing and a second bearing; the first bearing, the first bearing seat and the third bearing seat are matched, and the second bearing, the second bearing seat and the fourth bearing seat are matched; the first mass block is fixed in the shell by the first bearing, the first bearing seat and the third bearing seat, and the second mass block is fixed in the shell by the second bearing, the second bearing seat and the fourth bearing seat; the first mass block can rotate around the axial direction of the first bearing, and the second mass block can rotate around the axial direction of the second bearing.

[0013] In a possible implementation of the first aspect, when there are two or more first fiber gratings, each first fiber grating is arranged in parallel between the upper end of the first mass block and the upper end of the second mass block; when there are two or more second fiber gratings, each second fiber grating is arranged in parallel between the lower end of the first mass block and the lower end of the second mass block; the number of first fiber gratings and the number of second fiber gratings are the same or different.

[0014] In a possible implementation manner of the first aspect, arc-shaped grooves are formed on both the upper and lower surfaces of the flexible hinge, and the two grooves are symmetrical to each other.

[0015] In a possible implementation of the first aspect, when subjected to external vibration excitation, the first mass block and the second mass block simultaneously rotate around the axial direction of the first bearing and the axial direction of the second bearing respectively; accordingly, the first fiber grating is compressed or stretched, and / or the second fiber grating is stretched or compressed.

[0016] In a second aspect, an embodiment of the present application provides a measurement method for an FBG acceleration sensor based on a bearing and a flexible hinge, which is applied to an FBG acceleration sensor based on a bearing and a flexible hinge as in any one of the first aspect; when external vibrations occur, the first mass block and the second mass block rotate simultaneously around the axial direction of the first bearing and the axial direction of the second bearing, respectively; accordingly, the first fiber grating is compressed or stretched, generating an axial strain causing the central wavelength of the first fiber grating to change, and / or the second fiber grating is stretched or compressed, generating an axial strain causing the central wavelength of the second fiber grating to change.

[0017] The measuring method comprises: obtaining relevant parameters of the central wavelength of the first fiber grating and / or relevant parameters of the central wavelength of the second fiber grating; and determining the vibration acceleration according to the relevant parameters of the central wavelength of the first fiber grating and / or relevant parameters of the central wavelength of the second fiber grating.

[0018] In a possible implementation of the second aspect, the relevant parameter of the center wavelength of the first fiber grating is the center wavelength variation of the first fiber grating, and the relevant parameter of the center wavelength of the second fiber grating is the center wavelength variation of the second fiber grating; the vibration acceleration is determined according to the relevant parameter of the center wavelength of the first fiber grating and / or the relevant parameter of the center wavelength of the second fiber grating, comprising: determining the vibration acceleration according to the center wavelength variation of the first fiber grating and / or the center wavelength variation of the second fiber grating based on a calculation formula for the first vibration acceleration; the calculation formula for the first vibration acceleration is:

[0019] a=(∑|Δλ1|+∑|Δλ2|) / S0

[0020] Wherein, a is the vibration acceleration, Δλ1 is the change in the central wavelength of each first fiber Bragg grating, Δλ2 is the change in the central wavelength of each second fiber Bragg grating, and S0 is the preset sensitivity; when the fiber Bragg grating includes only the first fiber Bragg grating, the relevant parameters of the second fiber Bragg grating are zero; when the fiber Bragg grating includes only the second fiber Bragg grating, the relevant parameters of the first fiber Bragg grating are zero.

[0021] In a possible implementation of the second aspect, the relevant parameters of the central wavelength of the first fiber grating include the central wavelength of the first fiber grating and the initial central wavelength of the first fiber grating, and the relevant parameters of the central wavelength of the second fiber grating include the central wavelength of the second fiber grating and the initial central wavelength of the second fiber grating; the initial central wavelength of the first fiber grating is the central wavelength when the first fiber grating does not generate vibration, and the initial central wavelength of the second fiber grating is the central wavelength when the second fiber grating does not generate vibration; the vibration acceleration is determined according to the relevant parameters of the central wavelength of the first fiber grating and / or the relevant parameters of the central wavelength of the second fiber grating, including: based on the calculation formula of the second vibration acceleration, the vibration acceleration is determined according to the central wavelength of the first fiber grating and the initial central wavelength of the first fiber grating, and / or, the central wavelength of the second fiber grating and the initial central wavelength of the second fiber grating; the calculation formula of the second vibration acceleration is:

[0022] a=[(∑λ1-∑λ2)-(∑λ 1B -∑λ 2B )] / S0

[0023] Where a is the vibration acceleration, λ1 is the center wavelength of each first fiber Bragg grating, λ2 is the center wavelength of each second fiber Bragg grating, and λ 1B is the initial center wavelength of each first fiber Bragg grating, λ 2B is the initial center wavelength of each second fiber grating, S0 is the preset sensitivity; when the fiber grating only includes the first fiber grating, the relevant parameters of the second fiber grating are zero; when the fiber grating only includes the second fiber grating, the relevant parameters of the first fiber grating are zero.

[0024] It can be understood that the beneficial effects of the second aspect mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0025] The FBG acceleration sensor and measurement method based on bearings and flexible hinges provided in the embodiments of the present application use a single flexible hinge to connect two mass blocks, and use a fiber grating structure and a dual bearing structure, which can improve the sensitivity and linearity of the FBG acceleration sensor, as well as increase the natural frequency, achieve accurate measurement of medium and high frequency vibration signals, eliminate temperature effects, and increase the frequency measurement range of the FBG acceleration sensor.

[0026] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 It is a structural schematic diagram of a FBG acceleration sensor based on a bearing and a flexible hinge provided in an embodiment of the present application;

[0029] Figure 2 is a structural schematic diagram of a FBG acceleration sensor based on a bearing and a flexible hinge provided in another embodiment of the present application;

[0030] Figure 3 It is a flow chart of a measurement method of a FBG acceleration sensor based on a bearing and a flexible hinge provided in an embodiment of the present application;

[0031] Figure 4 It is a schematic diagram of the working principle and structure of a FBG acceleration sensor based on a bearing and a flexible hinge provided in one embodiment of the present application;

[0032] Figure 5 It is a schematic diagram showing the variation of the natural frequency and sensitivity of the FBG acceleration sensor provided in one embodiment of the present application with various structural parameters.

[0033] Reference numerals:

[0034] 1: first mass block; 2: second mass block; 3: flexible hinge; 4: first bearing seat; 5: second bearing seat; 6: first fiber grating; 7: second fiber grating; 8: first extension rod; 9: second extension rod; 10: third extension rod; 11: fourth extension rod; 12: housing; 13: third bearing seat; 14: fourth bearing seat; 15: first bearing; 16: second bearing. DETAILED DESCRIPTION

[0035] The present application is described more clearly below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the effects of the present application, but are not intended to limit the present application in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present application. These all fall within the scope of protection of the present application.

[0036] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0037] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0038] In the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0039] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0040] In addition, the “plurality” mentioned in the embodiments of the present application should be interpreted as two or more.

[0041] Figure 1 FIG. 1 is a schematic diagram of the structure of a FBG acceleration sensor based on a bearing and a flexible hinge provided in an embodiment of the present application. Figure 1 As shown, the FBG acceleration sensor based on bearings and flexible hinges (hereinafter referred to as FBG acceleration sensor) includes: a first mass block 1, a second mass block 2, a flexible hinge 3, a first bearing seat 4, a second bearing seat 5 and a fiber grating.

[0042] The first mass block 1 and the second mass block 2 are arranged parallel to each other, and the side of the first mass block 1 and the second mass block 2 close to each other is the inner side. The first end of the flexible hinge 3 is connected to the inner side of the first mass block 1, and the second end of the flexible hinge 3 is connected to the inner side of the second mass block 2.

[0043] The first end of the first bearing seat 4 is connected to the center position of the outer side surface of the first mass block 1, and the first end of the second bearing seat 5 is connected to the center position of the outer side surface of the second mass block 2; the first bearing seat 4 and the second bearing seat 5 are respectively provided with a first bearing hole and a second bearing hole, and the axial direction of the bearing hole is perpendicular to the axial direction of the mass block; the opposite side of the inner side surface of the mass block is the outer side surface of the mass block.

[0044] The fiber grating includes a first fiber grating 6 and / or a second fiber grating 7. The first fiber grating 6 is arranged between the upper end of the first mass block 1 and the upper end of the second mass block 2, and / or the second fiber grating 7 is arranged between the lower end of the first mass block 1 and the lower end of the second mass block 2 ( Figure 1 The fiber grating includes a first fiber grating 6 and a second fiber grating 7 (see FIG. 1 ).

[0045] Optionally, the flexible hinge 3 can be a straight circular flexible hinge, and the upper and lower surfaces of the flexible hinge 3 are both provided with arc-shaped grooves, and the two grooves are symmetrical to each other, and the groove curve is a conic curve. Exemplarily, the first end and the second end of the flexible hinge 3 can be connected to the center position of the inner side surface of the first mass block 1 and the center position of the inner side surface of the second mass block 2, respectively, but are not limited to the center position of the inner side surface of the mass block. It should be noted that when not subjected to external vibration excitation, the axial direction of the mass block is parallel to the vertical direction.

[0046] Exemplarily, a single flexible hinge 3 is used to connect two mass blocks, which can improve the sensitivity of the FBG acceleration sensor and avoid the problem of reduced linearity and reduced natural frequency of the FBG acceleration sensor caused by a multi-hinge structure. The two mass blocks are connected by a single flexible hinge 3, which can ensure that when subjected to external vibration excitation, the two mass blocks can vibrate up and down at the same time and will not rotate in the same direction in the low-order mode, thereby enabling the FBG acceleration sensor to have a wide frequency measurement range. The use of a dual fiber grating structure makes the axial strain directions of the two fiber gratings opposite, which can improve the sensitivity of the FBG acceleration sensor while eliminating the temperature effect. It should be noted that the dual fiber grating structure refers to a fiber grating that includes both a first fiber grating 6 and a second fiber grating 7.

[0047] Optionally, when there are two or more first fiber gratings 6, each first fiber grating 6 is arranged in parallel between the upper end of the first mass block 1 and the upper end of the second mass block 2. When there are two or more second fiber gratings 7, each second fiber grating 7 is arranged in parallel between the lower end of the first mass block 1 and the lower end of the second mass block 2. The number of the first fiber gratings 6 and the number of the second fiber gratings 7 are the same or different.

[0048] Exemplarily, when the fiber Bragg grating includes only the first fiber Bragg grating 6, and the fiber Bragg grating includes both the first fiber Bragg grating 6 and the second fiber Bragg grating 7, there is at least one first fiber Bragg grating 6. When the fiber Bragg grating includes only the second fiber Bragg grating 7, and the fiber Bragg grating includes both the first fiber Bragg grating 6 and the second fiber Bragg grating 7, there is at least one second fiber Bragg grating 7.

[0049] Optional, see Figure 1 The FBG acceleration sensor based on the bearing and the flexible hinge further includes: a first extension rod 8, a second extension rod 9, a third extension rod 10 and a fourth extension rod 11.

[0050] The first extension rod 8 and the second extension rod 9 are respectively arranged on the upper and lower surfaces of the first mass block 1, and are extended along the axial direction of the first mass block 1; the third extension rod 10 and the fourth extension rod 11 are respectively arranged on the upper and lower surfaces of the second mass block 2, and are extended along the axial direction of the second mass block 2. The first fiber grating 6 is arranged between the free end of the first extension rod 8 and the free end of the third extension rod 10, and the second fiber grating 7 is arranged between the free end of the second extension rod 9 and the free end of the fourth extension rod 11.

[0051] Exemplarily, the first fiber Bragg grating 6 and the second fiber Bragg grating 7 are respectively applied with a first prestress and a second prestress when they are set. Specifically, the first fiber Bragg grating 6 is pasted between the free ends of the first extension rod 8 and the third extension rod 10 by a two-point packaging method, and the second fiber Bragg grating 7 is pasted between the free ends of the second extension rod 9 and the fourth extension rod 11 by a two-point packaging method, and the first prestress and the second prestress are respectively applied when pasting the first fiber Bragg grating 6 and the second fiber Bragg grating 7 to avoid the chirp effect, and the first prestress can be the same as or different from the second prestress.

[0052] Optionally, when there are two or more first fiber gratings 6, each first fiber grating 6 is arranged in parallel between the free end of the first extension rod 8 and the free end of the third extension rod 10. When there are two or more second fiber gratings 7, each second fiber grating 7 is arranged in parallel between the free end of the second extension rod 9 and the free end of the fourth extension rod 11.

[0053] Optional, see Figure 2 The FBG acceleration sensor based on bearings and flexible hinges may also include: a housing 12 , a third bearing seat 13 and a fourth bearing seat 14 .

[0054] The third bearing seat 13 and the fourth bearing seat 14 are respectively provided at the center positions of the left and right inner sides of the housing 12. The third bearing seat 13 and the fourth bearing seat 14 are respectively provided with a third bearing hole and a fourth bearing hole, and the axial direction of the bearing hole is perpendicular to the axial direction of the housing 12.

[0055] It should be noted that the axial direction of the housing 12 is parallel to the vertical direction.

[0056] Optional, see Figure 2 The FBG acceleration sensor based on the bearing and the flexible hinge may further include: a first bearing 15 and a second bearing 16 .

[0057] The first bearing 15 and the first bearing seat 4 match the third bearing seat 13, and the second bearing 16 and the second bearing seat 5 match the fourth bearing seat 14. The first mass block 1 is fixed in the housing 12 through the first bearing 15, the first bearing seat 4 and the third bearing seat 13, and the second mass block 2 is fixed in the housing 12 through the second bearing 16, the second bearing seat 5 and the fourth bearing seat 14.

[0058] Exemplarily, the first mass block 1 can slightly rotate around the axial direction of the first bearing 15, and the second mass block 2 can slightly rotate around the axial direction of the second bearing 16. The first bearing 15 and the second bearing 16 can be deep groove ball bearings. The use of a single flexible hinge 3 to connect the two masses, supplemented by a dual bearing structure, can improve the sensitivity of the FBG acceleration sensor.

[0059] Optionally, when subjected to external vibration excitation, the first mass block 1 and the second mass block 2 rotate simultaneously around the axial direction of the first bearing 15 and the axial direction of the second bearing 16, respectively. Accordingly, the first fiber grating 6 is compressed or stretched, and / or the second fiber grating 7 is stretched or compressed. Wherein, when the fiber grating includes the first fiber grating 6 and the second fiber grating 7, if the first fiber grating 6 is compressed, the second fiber grating 7 is stretched, and if the first fiber grating 6 is stretched, the second fiber grating 7 is compressed. The fiber grating generates axial strain, which causes the central wavelength of the fiber grating to change, and then the vibration acceleration can be determined according to the relationship between the vibration acceleration and the relevant parameters of the central wavelength of the fiber grating, that is, the medium and high frequency vibration signals are determined.

[0060] An FBG acceleration sensor based on a bearing and a flexible hinge provided in an embodiment of the present application uses a single flexible hinge to connect two mass blocks, and uses a fiber grating structure and a dual bearing structure, which can improve the sensitivity and linearity of the FBG acceleration sensor, as well as increase the natural frequency, achieve accurate measurement of medium and high frequency vibration signals, eliminate temperature effects, and increase the frequency measurement range of the FBG acceleration sensor.

[0061] Figure 3 FIG. 1 is a flow chart of a measurement method of a FBG acceleration sensor based on a bearing and a flexible hinge provided in an embodiment of the present application. Figure 3 As shown, the above measurement method is applied to a FBG acceleration sensor based on a bearing and a flexible hinge, and the measurement method includes:

[0062] Step 101: Obtain parameters related to the center wavelength of a first fiber Bragg grating and / or parameters related to the center wavelength of a second fiber Bragg grating.

[0063] Step 102: Determine the vibration acceleration according to the relevant parameters of the central wavelength of the first fiber Bragg grating and / or the relevant parameters of the central wavelength of the second fiber Bragg grating.

[0064] Among them, the above-mentioned FBG acceleration sensor based on bearings and flexible hinges is the FBG acceleration sensor based on bearings and flexible hinges provided in any embodiment of the present application.

[0065] It should be noted that, in step 101, obtaining the relevant parameters of the center wavelength of the first fiber Bragg grating or the relevant parameters of the center wavelength of the second fiber Bragg grating means that when the fiber Bragg grating only includes the first fiber Bragg grating, the central wavelength of the first fiber Bragg grating is obtained, and when the fiber Bragg grating only includes the second fiber Bragg grating, the central wavelength of the second fiber Bragg grating is obtained. Similarly, in step 102, determining the vibration acceleration according to the relevant parameters of the center wavelength of the first fiber Bragg grating or the relevant parameters of the center wavelength of the second fiber Bragg grating means that when the fiber Bragg grating only includes the first fiber Bragg grating, the vibration acceleration is determined according to the relevant parameters of the center wavelength of the first fiber Bragg grating, and when the fiber Bragg grating only includes the second fiber Bragg grating, the vibration acceleration is determined according to the relevant parameters of the center wavelength of the second fiber Bragg grating.

[0066] Exemplarily, when external vibration occurs, the first mass block and the second mass block rotate around the axial direction of the first bearing and the axial direction of the second bearing respectively at the same time. Accordingly, the first fiber grating is compressed or stretched, generating axial strain causing the central wavelength of the first fiber grating to change, and / or the second fiber grating is stretched or compressed, generating axial strain causing the central wavelength of the second fiber grating to change. The vibration acceleration is determined according to the relevant parameters of the central wavelength of the fiber grating.

[0067] In a possible implementation, the relevant parameter of the center wavelength of the first fiber Bragg grating is the center wavelength variation of the first fiber Bragg grating, and the relevant parameter of the center wavelength of the second fiber Bragg grating is the center wavelength variation of the second fiber Bragg grating. Step 102 may include:

[0068] Based on the calculation formula of the first vibration acceleration, the vibration acceleration is determined according to the central wavelength change of the first fiber grating and / or the central wavelength change of the second fiber grating.

[0069] Among them, the calculation formula of the first vibration acceleration is:

[0070] a=(∑|Δλ1|+∑|Δλ2|) / S0 (1)

[0071] Wherein, a is the vibration acceleration, Δλ1 is the change in the central wavelength of each first fiber Bragg grating, Δλ2 is the change in the central wavelength of each second fiber Bragg grating, and S0 is the preset sensitivity. When the fiber Bragg grating includes only the first fiber Bragg grating, the relevant parameters of the second fiber Bragg grating are zero; when the fiber Bragg grating includes only the second fiber Bragg grating, the relevant parameters of the first fiber Bragg grating are zero.

[0072] The center wavelength variation of the first fiber Bragg grating and the center wavelength variation of the second fiber Bragg grating can be obtained by a fiber Bragg grating demodulator. The preset sensitivity is the calibration sensitivity of the FBG acceleration sensor.

[0073] It should be noted that, from the calculation formula of the first vibration acceleration, when there are two or more first fiber gratings, the center wavelength change of the first fiber grating is the sum of the center wavelength changes of each first fiber grating. When there are two or more second fiber gratings, the center wavelength change of the second fiber grating is the sum of the center wavelength changes of each second fiber grating.

[0074] In another possible implementation, the parameters related to the center wavelength of the first fiber Bragg grating include the center wavelength of the first fiber Bragg grating and the initial center wavelength of the first fiber Bragg grating, and the parameters related to the center wavelength of the second fiber Bragg grating include the center wavelength of the second fiber Bragg grating and the initial center wavelength of the second fiber Bragg grating. The initial center wavelength of the first fiber Bragg grating is the center wavelength when the first fiber Bragg grating does not vibrate, and the initial center wavelength of the second fiber Bragg grating is the center wavelength when the second fiber Bragg grating does not vibrate, and step 102 may include:

[0075] Based on the calculation formula of the second vibration acceleration, the vibration acceleration is determined according to the central wavelength of the first fiber grating and the initial central wavelength of the first fiber grating, and / or the central wavelength of the second fiber grating and the initial central wavelength of the second fiber grating.

[0076] Among them, the calculation formula of the second vibration acceleration is:

[0077] a=[(∑λ1-∑λ2)-(∑λ 1B -∑λ 2B )] / S0 (2)

[0078] Where a is the vibration acceleration, λ1 is the center wavelength of each first fiber Bragg grating, λ2 is the center wavelength of each second fiber Bragg grating, and λ 1B is the initial center wavelength of each first fiber Bragg grating, λ 2B is the initial center wavelength of each second fiber grating, and S0 is the preset sensitivity. When the fiber grating only includes the first fiber grating, the relevant parameters of the second fiber grating are zero; when the fiber grating only includes the second fiber grating, the relevant parameters of the first fiber grating are zero.

[0079] It should be noted that, from the calculation formula of the second vibration acceleration, when there are two or more first fiber gratings, the center wavelength of the first fiber grating is the sum of the center wavelengths of the first fiber gratings, and the initial center wavelength of the first fiber grating is the sum of the initial center wavelengths of the first fiber gratings. When there are two or more second fiber gratings, the center wavelength of the second fiber grating is the sum of the center wavelengths of the second fiber gratings, and the initial center wavelength of the second fiber grating is the sum of the initial center wavelengths of the second fiber gratings.

[0080] The center wavelength of the first fiber Bragg grating and the center wavelength of the second fiber Bragg grating can be obtained by a fiber Bragg grating demodulator and are measured values. The preset sensitivity is the calibration sensitivity of the FBG acceleration sensor. The above measurement method can avoid the influence of temperature on the center wavelength of the fiber Bragg grating, thereby eliminating the influence of temperature on the vibration acceleration calculation and improving the accuracy of the vibration acceleration.

[0081] Optionally, the sensitivity and frequency measurement range of the FBG accelerometer are controlled by adjusting the minimum thickness of the flexible hinge. That is, the sensitivity and frequency measurement range of the FBG accelerometer can be adjusted by adjusting the minimum thickness of the flexible hinge. The smaller the minimum thickness of the flexible hinge, the higher the sensitivity of the FBG accelerometer, but the corresponding frequency measurement range is narrower. As can be seen from the foregoing, the flexible hinge is provided with two symmetrical grooves, the groove curve is a conic curve, and the minimum thickness of the flexible hinge is the distance between the vertices of the two conic curves.

[0082] The embodiment of the present application provides a measurement method for a FBG acceleration sensor based on a bearing and a flexible hinge, which can achieve accurate measurement of medium and high frequency vibration signals by acquiring and determining the vibration acceleration according to relevant parameters of the central wavelength of the fiber grating.

[0083] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0084] In order to determine the structural parameters of the FBG accelerometer, a theoretical analysis of the FBG accelerometer is performed below. The analysis is performed by taking the case where the number of the first fiber grating is 1 and the number of the second fiber grating is 1 as an example. For ease of description, the fiber grating is referred to as FBG, the first fiber grating is referred to as FBG1, and the second fiber grating is referred to as FBG2.

[0085] The central wavelength changes of FBG1 and FBG2 can be expressed as:

[0086] Δλ1=(1-Pe )ε1λ1+(α f +ξ)ΔTλ1 (3)

[0087] Δλ2=(1-P e )ε2λ2+(α f +ξ)ΔTλ2 (4)

[0088] Where Δλ1 is the change in the center wavelength of FBG1, Δλ2 is the change in the center wavelength of FBG2, and P e is the effective elastic-optic coefficient, ε1 and ε2 are the axial strains of FBG1 and FBG2, λ1 and λ2 are the central wavelengths of FBG1 and FBG2, and α f is the thermal expansion coefficient of the optical fiber, ξ is the thermo-optic coefficient of the optical fiber material, and ΔT is the temperature change.

[0089] Among them, when stimulated by external vibration, FBG1 and FBG2 are stretched and compressed respectively, and the central wavelength changes of FBG1 and FBG2 are equal in magnitude and opposite in direction, that is, ε1=|-ε2|=ε. The central wavelengths of FBG1 and FBG2 are similar, that is, λ1≈λ2=λ.

[0090] The total wavelength change Δλ of the fiber Bragg grating is expressed as:

[0091] Δλ=Δλ1-Δλ2=2(1-P e )λε (5)

[0092] When the mass block (including the first mass block and the second mass block) is excited by vertical vibration acceleration, according to Newton's second law:

[0093] F=Kx m =M e a (6)

[0094] Where K is the system stiffness (i.e., the equivalent total stiffness of the system), x m is the displacement of the mass block, M e is the system equivalent mass, where the system refers to the vibration system of the entire designed FBG accelerometer structure.

[0095] When the vibration acceleration is in the upward direction, due to inertia, the mass block rotates downward relative to the bearing. According to the moment balance, when the rotation angle of the mass block is θ, the mass block is subjected to the elastic force F in the vertical direction of the flexible hinge. h The vertical tension F transmitted to the mass center by the fiber Bragg grating f The rotation occurs, such as Figure 4 As shown in (a) in the figure. Since the rotation angle is very small, F h and F fIt is regarded as a vertical force, and its resultant force is F, which is F in formula (6).

[0096] Reference Figure 4 (a) and Figure 4 In (b), the first mass block is used as an example to describe the displacement of the first mass block and the stretching length of FBG1.

[0097] x m =L1θ (7)

[0098] x f =Lθ (8)

[0099] In the formula, x f is the stretching length of FBG1, L1 is the horizontal distance from the center of the first bearing to the center of mass of the first mass block, L is the vertical distance from the center of mass of the first mass block to the sticking point of FBG1 (i.e., the distance from the center of mass of the mass block to the end of the extension rod), and θ is the rotation angle of the first mass block. It should be noted that the displacement of the second mass block and the stretching length of FBG2 can refer to the displacement of the first mass block and the stretching length of FBG1, which will not be repeated here.

[0100] The rotational stiffness of the flexible hinge and the stiffness of the FBG are:

[0101]

[0102]

[0103] In the formula, k h is the rotational stiffness of the flexible hinge, k f is the stiffness of FBG, s = R / t, E is the elastic modulus of the material (here the elastic modulus of 304 stainless steel is taken), R is the cutting radius of the flexible hinge, the flexible hinge is a straight circular flexible hinge, t is the minimum thickness of the flexible hinge, i is the depth of the flexible hinge, and E f is the elastic modulus of FBG (i.e., optical fiber elastic modulus), A f is the cross-sectional area of ​​FBG (i.e., the cross-sectional area of ​​optical fiber), and y is the length of FBG, i.e., the distance between the two mass blocks.

[0104] According to the torque balance, we have

[0105]

[0106] F f L1=2k f x f L (12)

[0107] In the formula, F h F is the elastic force in the vertical direction of the flexible hinge on the mass block, fIt is the vertical pulling force transmitted by FBG to the center of mass of the mass block.

[0108] The system stiffness K is:

[0109]

[0110] The total moment of inertia J of the mass block and the upper and lower extension rods is:

[0111]

[0112] In the formula, m and m b are the masses of the mass block and the extension rods (the extension rods include the first extension rod, the second extension rod, the third extension rod and the fourth extension rod) respectively, h is the height of the mass block, and b is the length of the mass block.

[0113] From the law of conservation of mechanical energy, we get

[0114]

[0115] From formula (13) and formula (15), we can know that the natural frequency f of the FBG acceleration sensor is:

[0116]

[0117] When the external vibration acceleration acts on the mass block, the moment balance equation of the mass block and the flexible hinge is:

[0118]

[0119] From formula (8) and formula (17), it can be seen that the single FBG strain (i.e., the axial strain of FBG) ε is:

[0120]

[0121] From formula (17), we can know that the sensitivity of the FBG accelerometer is:

[0122]

[0123] Among them, λ B is the central wavelength of FBG (λ1 or λ2), the sensitivity of FBG accelerometer is the single-gate sensitivity of FBG accelerometer, and the total sensitivity of FBG accelerometer is the superposition of two single-gate sensitivities, i.e. 2S. It can be seen from formula (19) that the natural frequency f of FBG accelerometer and the sensitivity S of FBG accelerometer limit each other, and increasing f or S will lead to a decrease in the other parameter.

[0124] In summary, the structural parameters that have a greater impact on the natural frequency and sensitivity of the FBG accelerometer are: the length of the FBG (i.e., the effective length of the optical fiber) y, the cutting radius of the flexible hinge R, the minimum thickness of the flexible hinge t, the depth of the flexible hinge i, the mass block length b, the mass block width c, the mass block height h, and the distance L from the mass block center of mass to the end of the extension rod. The schematic diagram of the natural frequency and sensitivity of the FBG accelerometer changing with each structural parameter is shown in Figure 5 See Figure 5 Except for the effective length y of the optical fiber, the natural frequency and sensitivity of the FBG accelerometer change in the opposite direction with the increase of each structural parameter, that is, the natural frequency and sensitivity of the FBG accelerometer limit each other.

[0125] In order to meet the test requirements of medium and high frequency vibration signals, the FBG accelerometer should have both a wide frequency measurement range and high sensitivity. Figure 5 From (a) in the figure, we can see that the natural frequency of the FBG accelerometer (hereinafter referred to as the natural frequency) and the sensitivity of the FBG accelerometer (hereinafter referred to as the sensitivity) decrease as the effective length y of the optical fiber increases. For the flexible hinge, its parameter values ​​mainly affect the system stiffness and natural frequency. Since the width between the two mass blocks is equal to the effective length of the optical fiber, the cutting radius R of the flexible hinge is half of the width between the two mass blocks. Figure 5 From (b) in the figure, we can see that the natural frequency increases with the minimum thickness t of the flexible hinge. However, when t / R>0.85, the error of the stiffness of the flexible hinge is large. When 0.25<t / R<0.85, the error is 10~20%. Figure 5 As shown in (c), the natural frequency increases with the depth i of the flexible hinge. However, the increase in the depth i of the flexible hinge will increase the difficulty of processing. When the depth i of the flexible hinge is small, it cannot meet the test requirements.

[0126] For the mass block, Figure 5 (d) and Figure 5 From (e) in the figure, we can see that the mass block width c and mass block height h have a greater impact on sensitivity than on natural frequency. Therefore, the mass block width c and mass block height h should be as large as possible to increase sensitivity, but too large will affect the overall size. Figure 5 From (f) in the figure, we can see that the mass block length b should take into account both sensitivity and natural frequency. Its value should be as small as possible to increase the natural frequency, but it should not be less than 4mm, otherwise the package will not be firm. Figure 5From (g), we can see that when the distance L from the center of mass of the mass block to the end of the extension rod is less than 20mm, the natural frequency does not change much with the increase of L, but the sensitivity increases rapidly with the increase of L. When 20mm<L<35mm, the natural frequency decreases with the increase of L, and the sensitivity increases slowly with the increase of L. When L>35mm, the natural frequency decreases rapidly with the increase of L, and the sensitivity begins to decrease slowly with the increase of L. In summary, determining the structural parameters of the FBG accelerometer according to the above theoretical analysis can ensure that the FBG accelerometer has both a higher frequency measurement range and a higher sensitivity. According to the above theoretical analysis to determine the structural parameters of the FBG accelerometer, it can be obtained that the theoretical natural frequency of the FBG accelerometer is 3667.7Hz, and the theoretical sensitivity (i.e., single-gate sensitivity) is 16.10pm / g.

[0127] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A FBG acceleration sensor based on a bearing and a flexible hinge, characterized in that: include: A first mass block, a second mass block, a flexible hinge, a first bearing seat, a second bearing seat and a fiber grating; The first mass block and the second mass block are arranged parallel to each other, and the side surfaces of the first mass block and the second mass block close to each other are inner side surfaces; the first end of the flexible hinge is connected to the inner side surface of the first mass block, and the second end of the flexible hinge is connected to the inner side surface of the second mass block; The first end of the first bearing seat is connected to the center of the outer side surface of the first mass block, and the first end of the second bearing seat is connected to the center of the outer side surface of the second mass block; the first bearing seat and the second bearing seat are respectively provided with a first bearing hole and a second bearing hole, and the axial direction of the bearing hole is perpendicular to the axial direction of the mass block; the side opposite to the inner side surface of the mass block is the outer side surface of the mass block; The fiber Bragg grating includes a first fiber Bragg grating and / or a second fiber Bragg grating; the first fiber Bragg grating is arranged between the upper end of the first mass block and the upper end of the second mass block, and / or the second fiber Bragg grating is arranged between the lower end of the first mass block and the lower end of the second mass block; The FBG acceleration sensor based on bearings and flexible hinges further comprises: a housing, a third bearing seat and a fourth bearing seat, and a first bearing and a second bearing; A third bearing seat and a fourth bearing seat are respectively arranged at the center positions of the left and right inner sides of the housing; The third bearing seat and the fourth bearing seat are respectively provided with a third bearing hole and a fourth bearing hole, and the axial direction of the bearing hole is perpendicular to the axial direction of the housing; The first bearing and the first bearing seat match the third bearing seat, and the second bearing and the second bearing seat match the fourth bearing seat; The first mass block is fixed in the shell by the first bearing, the first bearing seat and the third bearing seat, and the second mass block is fixed in the shell by the second bearing, the second bearing seat and the fourth bearing seat; the first mass block can rotate around the axial direction of the first bearing, and the second mass block can rotate around the axial direction of the second bearing.

2. The FBG acceleration sensor based on bearings and flexible hinges according to claim 1, characterized in that: The FBG acceleration sensor based on the bearing and the flexible hinge further comprises: a first extension rod, a second extension rod, a third extension rod and a fourth extension rod; The first extension rod and the second extension rod are respectively arranged on the upper and lower surfaces of the first mass block, and are extended along the axial direction of the first mass block; the third extension rod and the fourth extension rod are respectively arranged on the upper and lower surfaces of the second mass block, and are extended along the axial direction of the second mass block; The first fiber Bragg grating is disposed between the free end of the first extension rod and the free end of the third extension rod, and / or the second fiber Bragg grating is disposed between the free end of the second extension rod and the free end of the fourth extension rod.

3. The FBG acceleration sensor based on bearings and flexible hinges according to claim 1, characterized in that: When there are two or more first fiber gratings, each first fiber grating is arranged in parallel between the upper end of the first mass block and the upper end of the second mass block; When there are two or more second fiber gratings, each second fiber grating is arranged in parallel between the lower end of the first mass block and the lower end of the second mass block; The number of the first fiber gratings and the number of the second fiber gratings are the same or different.

4. The FBG acceleration sensor based on bearings and flexible hinges according to claim 1, characterized in that: The upper and lower surfaces of the flexible hinge are both provided with arc-shaped grooves, and the two grooves are symmetrical to each other.

5. The FBG acceleration sensor based on bearings and flexible hinges according to claim 1, characterized in that: When subjected to external vibration excitation, the first mass block and the second mass block rotate simultaneously around the axial direction of the first bearing and the axial direction of the second bearing respectively; Correspondingly, the first fiber grating is compressed or stretched, and / or the second fiber grating is stretched or compressed.

6. A measurement method of a FBG acceleration sensor based on a bearing and a flexible hinge, characterized in that: The FBG acceleration sensor based on bearings and flexible hinges according to any one of claims 1 to 5 is applied; when external vibration occurs, the first mass block and the second mass block rotate around the axial direction of the first bearing and the axial direction of the second bearing respectively at the same time; accordingly, the first fiber Bragg grating is compressed or stretched, generating axial strain causing the central wavelength of the first fiber Bragg grating to change, and / or the second fiber Bragg grating is stretched or compressed, generating axial strain causing the central wavelength of the second fiber Bragg grating to change; The measuring method comprises: Acquire relevant parameters of the center wavelength of the first fiber grating and / or relevant parameters of the center wavelength of the second fiber grating; The vibration acceleration is determined according to parameters related to the center wavelength of the first fiber grating and / or parameters related to the center wavelength of the second fiber grating.

7. The measurement method of the FBG acceleration sensor based on a bearing and a flexible hinge according to claim 6 is characterized in that: The relevant parameter of the central wavelength of the first fiber Bragg grating is the central wavelength variation of the first fiber Bragg grating, and the relevant parameter of the central wavelength of the second fiber Bragg grating is the central wavelength variation of the second fiber Bragg grating; Determining the vibration acceleration according to the relevant parameters of the center wavelength of the first fiber grating and / or the relevant parameters of the center wavelength of the second fiber grating includes: Based on a calculation formula of a first vibration acceleration, determining the vibration acceleration according to a change in the center wavelength of the first fiber grating and / or a change in the center wavelength of the second fiber grating; The calculation formula of the first vibration acceleration is: a=(∑|Δλ1|+∑|Δλ2|) / S0 Wherein, a is the vibration acceleration, Δλ1 is the change in the central wavelength of each first fiber Bragg grating, Δλ2 is the change in the central wavelength of each second fiber Bragg grating, and S0 is the preset sensitivity; when the fiber Bragg grating includes only the first fiber Bragg grating, the relevant parameters of the second fiber Bragg grating are zero; when the fiber Bragg grating includes only the second fiber Bragg grating, the relevant parameters of the first fiber Bragg grating are zero.

8. The measurement method of the FBG acceleration sensor based on a bearing and a flexible hinge according to claim 6, characterized in that: The parameters related to the center wavelength of the first fiber grating include the center wavelength of the first fiber grating and the initial center wavelength of the first fiber grating, and the parameters related to the center wavelength of the second fiber grating include the center wavelength of the second fiber grating and the initial center wavelength of the second fiber grating; the initial center wavelength of the first fiber grating is the center wavelength when the first fiber grating does not vibrate, and the initial center wavelength of the second fiber grating is the center wavelength when the second fiber grating does not vibrate; Determining the vibration acceleration according to the relevant parameters of the center wavelength of the first fiber grating and / or the relevant parameters of the center wavelength of the second fiber grating includes: Based on a calculation formula for the second vibration acceleration, the vibration acceleration is determined according to the center wavelength of the first fiber grating and the initial center wavelength of the first fiber grating, and / or the center wavelength of the second fiber grating and the initial center wavelength of the second fiber grating; The calculation formula of the second vibration acceleration is: a=[(∑λ1-∑λ2)-(∑λ 1B -∑λ 2B )] / S0 Where a is the vibration acceleration, λ1 is the center wavelength of each first fiber Bragg grating, λ2 is the center wavelength of each second fiber Bragg grating, and λ 1B is the initial center wavelength of each first fiber Bragg grating, λ 2B is the initial center wavelength of each second fiber grating, S0 is the preset sensitivity; when the fiber grating only includes the first fiber grating, the relevant parameters of the second fiber grating are zero; when the fiber grating only includes the second fiber grating, the relevant parameters of the first fiber grating are zero.

Images