MEMS gravimeter probe and gravimeter based on dual-path offset array capacitive displacement sensor

Abstract

The present invention discloses a closed-loop MEMS gravimeter probe and a gravimeter based on dual-channel offset array capacitive displacement sensing, belonging to the field of instrumentation. The probe includes: a capacitive displacement sensing module, a capacitive detection circuit module, a PID control module and a feedback actuator module, and these modules constitute a magnetic closed loop. The capacitive displacement sensing module includes two parallel moving pole plate arrays that are offset by m / 4 pole plate periods, wherein m is a positive integer, and when the displacement sensor formed by one of the moving pole plate arrays and the fixed pole plate array is in a non-sensitive interval, the displacement sensor formed by the other moving pole plate array and the fixed pole plate array is just in a sensitive interval and is used to detect the displacement of the vibrator. The probe of the present invention can effectively avoid the problem of displacement detection failure caused by the uncontrollable sagging amount of the mass block output of the existing single-channel array pole plate, improve the detection sensitivity, and adopt a closed-loop working mode to improve the probe response time, and has a stronger anti-interference ability.

Description

Technical Field

[0001] The present invention belongs to the field of instruments and meters, and more specifically, relates to a closed-loop MEMS gravimeter probe and a gravimeter based on dual-path offset array capacitive displacement sensing. Background Art

[0002] Accurately measuring tiny changes in gravitational acceleration is of great significance for the causes and early warning of natural disasters, oil and gas resource exploration, and basic geophysical research. Although free-fall gravimeters, cold atom gravimeters, spring gravimeters, and superconducting gravimeters all have high-sensitivity detection capabilities, they generally have the limitations of high cost and large size. MEMS sensors processed using chip technology are expected to solve this problem due to their mass production, light weight, and small size.

[0003] In recent years, the development of relative gravimeters using MEMS technology has become a hot topic in industry research. The University of Glasgow was the first to use a negative stiffness spring mass block system in conjunction with an optical shadow displacement sensor to successfully achieve solid earth tide measurement in the laboratory (Middlemiss.R.et al.Nature 531,614–617,2016). In the team's latest research results, the displacement sensing method was improved to an array capacitive type, with a self-noise level of 7μGal / √Hz in open-loop working mode (D.Carbone.etal.Frontiers in earth science 8,452,2020). Similar work also includes (CN107092038B, Xiaochao Xu.et al.IEEE Sensors Journal 21(20),22480–22488,2021) and so on.

[0004] However, these MEMS gravimeters are all in open-loop working mode. They will face problems such as poor environmental adaptability and slow response speed in field mobile gravity measurement, which limits the scope of application of MEMS gravimeters. In addition, the design value of the detection displacement range of the array capacitor displacement detection unit in a single cycle is only on the order of hundreds of microns. More importantly, due to the error in the MEMS processing technology, the spring consistency of the gravity sensitive unit is poor, which leads to uncontrollable sagging of the mass block under the action of gravity, making it possible for the array capacitor to work in an insensitive area, resulting in a decrease in the sensitivity of the gravimeter sensor or even detection. Summary of the invention

[0005] In view of the defects of the prior art and the need for improvement, the present invention provides a closed-loop MEMS gravimeter probe and a gravimeter based on dual-path offset array capacitive displacement sensing, the purpose of which is to improve the detection sensitivity of the gravimeter probe.

[0006] To achieve the above object, according to one aspect of the present invention, a closed-loop MEMS gravimeter probe based on dual-path offset array capacitive displacement sensing is provided, comprising:

[0007] A capacitive displacement sensing module comprises a spring-oscillator structure, a fixed electrode plate array, two moving electrode plate arrays and an upper cover; the two moving electrode plate arrays are arranged on the spring-oscillator structure, the two moving electrode plate arrays are arranged in parallel, and are staggered by m / 4 electrode periods, wherein m is a positive integer; the fixed electrode plate array is arranged on the upper cover, the two moving electrode plate arrays respectively form a capacitive displacement sensing structure with the fixed electrode plate array, and are used to convert the relative change of the gravitational acceleration to be measured into a capacitance change;

[0008] A capacitance detection circuit module, used for detecting the capacitance change and converting the capacitance change into a voltage representing the relative change of the gravitational acceleration to be measured;

[0009] A PID control module, used to use the voltage as input and, through a PID control algorithm, calculate a feedback adjustment voltage required to return the mass block in the spring-oscillator structure to a balanced state;

[0010] The feedback actuator module is used to convert the feedback regulation voltage into current, generate Ampere force in the magnetic field and keep the spring-oscillator structure in a balanced state.

[0011] Furthermore, the feedback actuator module includes: a magnetic circuit structure, a feedback coil and a pressure-current conversion structure;

[0012] The magnetic circuit structure provides a magnetic field for the feedback coil;

[0013] The voltage-to-current conversion structure is used to convert the feedback regulation voltage into a current and input it into the feedback coil;

[0014] The feedback coil is used to form a current loop to generate the Ampere force in the magnetic field.

[0015] Furthermore, the voltage-to-current conversion structure includes a voltage-to-current conversion regulating resistor, and the current in the feedback coil is adjusted by changing the resistance value of the voltage-to-current conversion regulating resistor.

[0016] Furthermore, the current I flowing into the feedback coil and the feedback regulation voltage V output by the PID control module out And the voltage-current conversion regulating resistor meets the following requirements:

[0017]

[0018] Wherein, R is the resistance value of the voltage-current conversion regulating resistor.

[0019] Furthermore, the relative change Δg of the gravitational acceleration to be measured and the mass m of the mass block in the spring-oscillator structure satisfy:

[0020]

[0021] Where, F is the feedback coil subjected to the Ampere force.

[0022] Furthermore, the feedback regulation voltage V output by the PID control module out The relative change Δg of the gravitational acceleration to be measured satisfies:

[0023]

[0024] Wherein, N and L are the number of turns and effective length of the feedback coil respectively, B is the magnetic induction intensity provided by the magnetic circuit structure, and R is the resistance value of the voltage-current conversion regulating resistor.

[0025] Furthermore, the magnetic circuit structure includes a permanent magnet, a yoke and a pole piece, the permanent magnet is arranged on the yoke, and the pole piece is attached to the permanent magnet.

[0026] Furthermore, the capacitive displacement sensor module also includes a limiting column, and the upper cover maintains a fixed distance from the spring-oscillator structure through the limiting column.

[0027] Furthermore, the capacitance detection circuit module also includes a carrier circuit structure, which is used to provide a carrier and a demodulation wave for the capacitance detection circuit module to modulate and demodulate the capacitance change.

[0028] According to another aspect of the present invention, a MEMS gravimeter based on dual-path offset array capacitive displacement sensing is provided, comprising a MEMS gravimeter probe, wherein the MEMS gravimeter probe is the MEMS gravimeter probe based on dual-path offset array capacitive displacement sensing as described in any one of the first aspects.

[0029] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0030] (1) The present invention adopts a dual-channel offset array plate for displacement sensing. The two moving plate arrays are offset by m / 4 plate periods, where m is a positive integer. When the displacement sensor composed of one moving plate array and the fixed plate array is in a non-sensitive range, the displacement sensor composed of the other moving plate array and the fixed plate array is just in a sensitive range and is used to detect the displacement of the vibrator. The probe of the present invention can effectively avoid the problem of displacement detection failure caused by the uncontrollable droop of the mass block in the existing single-channel array plate output, thereby improving the detection sensitivity.

[0031] (2) The capacitive displacement sensor module, the capacitive detection circuit module, the PID control module and the feedback actuator module in the present invention constitute the magnetic closed loop of the gravimeter probe. Compared with the open-loop working mode of the existing MEMS gravimeter, it can not only make the gravimeter respond faster, but also improve the linearity (grid value accuracy), and improve the ability of the MEMS gravimeter sensitive unit to suppress external environmental interference. And through electromagnetic feedback control, the mass block is controlled near the equilibrium position, which improves the low-frequency drift problem caused by spring creep to a certain extent, improves the response speed of the sensitive unit to the signal, and is more suitable for field measurement.

[0032] In summary, the probe of the present invention is a high-precision magnetic closed-loop MEMS gravity sensor chip that uses a dual-path staggered array plate detection method to circumvent the nonlinear range of the array capacitor plate output, which can effectively avoid the problem of displacement detection failure caused by the uncontrollable sag of the mass block in the existing single-path array plate output; at the same time, the present invention uses the Ampere force exerted on the feedback coil under the magnetic field as the feedback force to make the spring-oscillator work in a closed-loop working mode near the equilibrium position, which can improve the response time and grid value accuracy of the gravimeter, making the gravimeter more suitable for field working environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the structure of the magnetic closed-loop MEMS gravimeter probe of the present invention;

[0034] Figure 2 It is the relationship between input displacement and output capacitance in single-channel plate array capacitive displacement sensing;

[0035] Figure 3 It is a schematic diagram of a dual-path staggered array plate displacement sensor structure;

[0036] Figure 4 It is the principle diagram of dual-path offset array plate displacement sensing;

[0037] Figure 5 1 is a graph showing the relationship between input displacement and output capacitance of a dual-path staggered plate array capacitive displacement sensor. In all drawings, the same reference numerals are used to represent the same elements or structures, wherein:

[0038] 1-permanent magnet, 2-yoke, 3-pole piece, 4-glass cover, 5-spring-oscillator structure, 6-feedback coil, 7-fixed pole plate array, 8-moving pole plate array, 9-limiting column, 10-signal lead-out point, 11-carrier circuit structure, 12-capacitance detection circuit module, 13-PID control module, 14-pressure-current conversion structure. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0040] In the present invention, the terms "first", "second", etc. in the present invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0041] like Figure 1 As shown, the closed-loop MEMS gravimeter probe based on dual-path offset array capacitive displacement sensing of the present invention is applied to precision gravity measurement and mainly includes:

[0042] The capacitive displacement sensor module is used to sense the relative change of the gravitational acceleration to be measured and convert the relative change of the gravitational acceleration to be measured into a capacitance change;

[0043] The capacitance detection circuit module 12 is used to detect the capacitance variation, and convert the capacitance variation into a corresponding voltage signal representing the relative variation of the gravitational acceleration to be measured after modulation and demodulation;

[0044] The PID control module 13 is used to calculate the deviation value between the relative change of the gravity acceleration to be measured and the acceleration actually measured by the controlled spring oscillator according to the functional relationship of proportion, integration and differentiation, and output the feedback adjustment voltage required to return the mass block to the equilibrium state through feedback adjustment output; wherein the deviation value between the relative change of the gravity acceleration to be measured and the acceleration actually measured by the controlled spring oscillator is obtained according to the voltage signal output by the capacitance detection circuit module in the open loop;

[0045] The feedback actuator module is used to convert the feedback regulation voltage into a current, and the current is applied to the feedback coil. The feedback coil arranged on the spring-oscillator structure is subjected to a magnetic feedback force proportional to the external gravitational acceleration to be measured in the magnetic field, so that the spring-oscillator structure maintains a balanced state;

[0046] Specifically, the capacitive displacement sensing module includes a spring-oscillator structure 5, a fixed electrode plate array 7, a two-way moving electrode plate array 8, a glass cover 4, a limiting column 9 and a signal lead-out point 10, wherein the fixed electrode plate array 7 is arranged on the glass cover 4, the two-way moving electrode plate array 8 is arranged on the spring-oscillator structure 5, the glass cover 4 maintains a fixed distance with the spring-oscillator structure 5 through the limiting column 9, and the signal lead-out point 10 is arranged on the glass cover 4, wherein the two-way moving electrode plate array 8 is placed in parallel and staggered, and the relative positions of the two-way moving electrode plate arrays are staggered by 1 / 4 of the plate period, and the two-way moving electrode plate arrays (pickup array plates) can respectively form a variable area capacitive displacement sensing structure with the fixed electrode plate array (driving plate) for converting the change of the external gravitational acceleration to be measured into capacitance. In other embodiments, the two-way moving electrode plate array can also be arranged with other integer multiples of 1 / 4 of the plate period. In other embodiments, the glass cover 4 can also be other fixed structures.

[0047] The capacitance detection circuit module includes a carrier circuit structure 11, which is used to provide a carrier and a demodulation wave for the circuit, so as to modulate and demodulate the capacitance signal output by the capacitance displacement sensing module and amplify the signal.

[0048] The feedback actuator module includes a magnetic circuit structure, a feedback coil 6 and a pressure-flow conversion structure 14; the magnetic circuit structure provides a uniform and stable magnetic field for the feedback coil; the pressure-flow conversion structure is used to convert the feedback adjustment voltage output by the PID control module into a current signal input into the feedback coil, and the current in the feedback coil can be adjusted by changing the size of the pressure-flow conversion adjustment resistor in the pressure-flow conversion structure to change the scale factor of the gravimeter; the feedback coil 6 is used to form a current loop, and in the corresponding magnetic field, the Ampere force exerted on the energized wire in the magnetic field is used to pull the mass block in the spring-oscillator structure back to the equilibrium position.

[0049] The magnetic circuit structure includes a permanent magnet 1, a yoke 2 and a pole piece 3, wherein the permanent magnet 1 is arranged on the yoke 2, and the pole piece 3 is attached to the permanent magnet 1. The yoke is used to conduct magnetism and form a magnetic circuit, and the pole piece is used to gather the magnetic field. The yoke, the pole piece and the permanent magnet are fixedly connected to form a uniform and large magnetic induction intensity. In practical applications, by designing the shape and parameters of the yoke and the pole piece, the magnetic circuit structure can have a large magnetic induction intensity while maintaining a strong uniformity of the magnetic induction intensity within a certain range.

[0050] By arranging two moving plate arrays with relative positions offset by 1 / 4 plate period on the spring-oscillator structure, the initial phases of the two moving plate arrays are different, so that the output phases of the displacement sensing curves of the two arrays differ by 1 / 4 period. When the output of one moving plate array is at the inflection point or in the low sensitivity interval, the output of the other moving plate array is in the displacement sensitive interval and can be output normally. When working, the feedback adjustment voltage V output by the PID control module is judgedout The linear transformation relationship between the relative change Δg of the gravitational acceleration to be measured can be used to determine whether to use the first moving electrode array or the second moving electrode array as the output array to avoid the non-sensitive area. Specifically, when the first moving electrode array is used as the output array, if the feedback regulation voltage V output by the PID control module is out If the relative change Δg of the gravitational acceleration to be measured cannot be responded to linearly, it means that the first moving electrode array is located in a low sensitivity area. At this time, the second moving electrode array is in a sensitive area because the output phase difference between the second moving electrode array and the first moving electrode array is 1 / 4 electrode period. By switching the second moving electrode array to the output array through the signal lead-out point 10, the problem of decreased linearity of displacement detection or even detection failure caused by uncontrollable sagging of the mass block can be solved, thereby improving the detection sensitivity of the probe.

[0051] The current in the feedback coil, the feedback regulation voltage output by the PID circuit module and the voltage-current conversion regulation resistor satisfy the following conditions:

[0052]

[0053] Where I is the current in the feedback coil, which is related to the scaling factor of the final output, R is the resistance of the voltage-to-current conversion adjustment resistor, and V out It is the feedback regulation voltage output by the PID circuit module.

[0054] The feedback coil is made of a conductive metal layer on a spring-oscillator structure prepared by a coating process. When current is passed through it, under the action of the magnetic field, the feedback coil is subjected to the Ampere force F as follows:

[0055] F=2NBIL (2)

[0056] Where N is the number of turns of the feedback coil, B is the magnetic induction intensity at the feedback coil, that is, the magnetic field provided by the magnetic circuit structure in the feedback actuator module, and L is the effective length of the feedback coil, that is, the average length of the feedback coil perpendicular to the sensitive axis (the direction of the gravitational acceleration to be measured).

[0057] According to Newton's second law, the relative change Δg of the gravitational acceleration to be measured can be expressed as:

[0058]

[0059] Where m is the mass of the mass block in the spring-oscillator structure.

[0060] Combining equations (1), (2) and (3), we can get the output of the closed-loop gravimeter, that is, the feedback regulation voltage V output by the PID circuit module. out expression:

[0061]

[0062] It can be seen that at this time, the output of the closed-loop gravimeter is only related to the mass m of the mass block, the number of turns of the feedback coil N, the magnetic field magnetic induction intensity B, the effective length L of the feedback coil, and the resistance R of the adjustment resistor. out The change in Δg is used to reflect the relative change in gravitational acceleration to be measured.

[0063] Compared with the open-loop system, the capacitive displacement sensor module, the capacitive detection circuit module, the PID control module and the feedback actuator module in the present invention constitute a magnetic closed-loop circuit. This closed-loop structure improves the ability of the sensitive unit (MEMS gravimeter probe) to suppress external interference and improves its response characteristics. At the same time, the resistance value of the resistor can be adjusted by pressure-current conversion to change the scale factor to adapt to different measurement environments. Through electromagnetic feedback control, the mass block is controlled near the equilibrium position, which improves the low-frequency drift problem caused by spring creep to a certain extent, improves the response speed of the sensitive unit to the signal, and is more suitable for field measurement.

[0064] like Figure 2 The figure shows the relationship between the input displacement and output capacitance of a single-channel plate array capacitive displacement sensor in one cycle. The figure shows that in the single-channel plate array detection, there is a low sensitivity interval for displacement detection, and the gravimeter cannot work normally. In addition, since the design value of the single-cycle displacement range of the capacitance detection is in the order of hundreds of microns, and the inconsistency of the beam stiffness caused by the process error makes it impossible to accurately control the sagging amount of the mass block under the action of gravity within the displacement interval, the single-channel plate array displacement sensing method will have a distortion problem, which seriously affects the detection of gravity acceleration. In the present invention, a dual-channel staggered array plate is used to avoid the nonlinear interval of the array capacitor plate output.

[0065] like Figure 3 As shown, it is a schematic diagram of a capacitive displacement sensing structure formed by two moving electrode plate arrays and a fixed electrode plate array. In this embodiment, the two moving electrode plate arrays are a left moving electrode plate array and a right moving electrode plate array. Figure 4 is the corresponding working state, and n in the figure represents the number of plates in the moving plate array, that is, n groups of variable area differential capacitance displacement sensors. It can be seen from the figure that the left moving plate array and the right moving plate array are staggered, and the relative position is staggered by 1 / 4 of the displacement period of the differential capacitor (composed of two fixed plates and one moving plate). Figure 5From the relationship diagram between the input displacement and output capacitance of the dual-channel staggered plate array capacitive displacement sensor, it can be seen that the output phase of the displacement sensing curves of the two arrays differs by 1 / 4 cycle. When one of the outputs is at the inflection point or the low sensitivity interval, the other output is in the displacement sensitive interval and can output normally. By selecting the output array to avoid the non-sensitive area, the problem of decreased displacement detection linearity or even detection failure caused by the uncontrollable sag of the mass block is solved.

[0066] The present invention also provides a MEMS gravimeter based on dual-path staggered array capacitive displacement sensing, comprising a MEMS gravimeter probe. The MEMS gravimeter probe is the above-mentioned MEMS gravimeter probe based on dual-path staggered array capacitive displacement sensing.

[0067] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A closed-loop MEMS gravimeter probe based on dual-path offset array capacitive displacement sensing, characterized in that: include: A capacitive displacement sensing module comprises a spring-oscillator structure, a fixed electrode plate array, two moving electrode plate arrays and an upper cover; the two moving electrode plate arrays are arranged on the spring-oscillator structure, the two moving electrode plate arrays are arranged in parallel, and are staggered by m / 4 electrode periods, wherein m is a positive integer; the fixed electrode plate array is arranged on the upper cover, the two moving electrode plate arrays respectively form a capacitive displacement sensing structure with the fixed electrode plate array, and are used to convert the relative change of the gravitational acceleration to be measured into a capacitance change; A capacitance detection circuit module, used for detecting the capacitance change and converting the capacitance change into a voltage representing the relative change of the gravitational acceleration to be measured; A PID control module, used to use the voltage as input and, through a PID control algorithm, calculate a feedback adjustment voltage required to return the mass block in the spring-oscillator structure to a balanced state; A feedback actuator module, used for converting the feedback regulation voltage into current, generating an Ampere force in a magnetic field to keep the spring-oscillator structure in a balanced state; During operation, by judging the linear transformation relationship between the feedback regulation voltage output by the PID control module and the relative change of the gravitational acceleration to be measured, the first moving electrode plate array or the second moving electrode plate array of the two moving electrode plate arrays is selected as the output array; specifically, when the first moving electrode plate array is used as the output array, if the feedback regulation voltage output by the PID control module cannot linearly reflect the change of the relative change of the gravitational acceleration to be measured, the first moving electrode plate array is switched as the output array.

2. The closed-loop MEMS gravimeter probe based on dual-path staggered array capacitive displacement sensing according to claim 1 is characterized in that: The feedback actuator module includes: a magnetic circuit structure, a feedback coil and a pressure-current conversion structure; The magnetic circuit structure provides a magnetic field for the feedback coil; The voltage-to-current conversion structure is used to convert the feedback regulation voltage into a current and input it into the feedback coil; The feedback coil is used to form a current loop to generate the Ampere force in the magnetic field.

3. The closed-loop MEMS gravimeter probe based on dual-path staggered array capacitive displacement sensing according to claim 2 is characterized in that: The voltage-to-current conversion structure includes a voltage-to-current conversion regulating resistor, and the current in the feedback coil is adjusted by changing the resistance value of the voltage-to-current conversion regulating resistor.

4. The closed-loop MEMS gravimeter probe based on dual-path staggered array capacitive displacement sensing according to claim 3 is characterized in that: The current I passed into the feedback coil and the feedback regulation voltage V output by the PID control module out And the voltage-current conversion regulating resistor meets the following requirements: Wherein, R is the resistance value of the voltage-current conversion regulating resistor.

5. The closed-loop MEMS gravimeter probe based on dual-path staggered array capacitive displacement sensing according to claim 4 is characterized in that: The relative change Δg of the gravitational acceleration to be measured and the mass m of the mass block in the spring-oscillator structure satisfy: Where, F is the feedback coil subjected to the Ampere force.

6. The closed-loop MEMS gravimeter probe based on dual-path staggered array capacitive displacement sensing according to claim 5, characterized in that: The PID control module outputs a feedback regulation voltage V out The relative change Δg of the gravitational acceleration to be measured satisfies: Wherein, N and L are the number of turns and effective length of the feedback coil respectively, B is the magnetic induction intensity provided by the magnetic circuit structure, and R is the resistance value of the voltage-current conversion regulating resistor.

7. The closed-loop MEMS gravimeter probe based on dual-path staggered array capacitive displacement sensing according to claim 6, characterized in that: The magnetic circuit structure comprises a permanent magnet, a yoke and a magnetic pole piece. The permanent magnet is arranged on the yoke, and the magnetic pole piece is attached to the permanent magnet.

8. The closed-loop MEMS gravimeter probe based on dual-path staggered array capacitive displacement sensing according to claim 1, characterized in that: The capacitive displacement sensor module further includes a limiting column, and the upper cover maintains a fixed distance from the spring-oscillator structure through the limiting column.

9. The closed-loop MEMS gravimeter probe based on dual-path staggered array capacitive displacement sensing according to claim 1, characterized in that: The capacitance detection circuit module also includes a carrier circuit structure, which is used to provide a carrier and a demodulation wave for the capacitance detection circuit module to modulate and demodulate the capacitance change.

10. A MEMS gravimeter based on dual-path offset array capacitive displacement sensing, comprising a MEMS gravimeter probe, characterized in that: The MEMS gravimeter probe is a MEMS gravimeter probe based on dual-path offset array capacitive displacement sensing as described in any one of claims 1 to 9.

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