Acceleration measurement method based on multi-mode micromechanical detection

Abstract

The invention discloses an acceleration measurement method based on multi-mode micro-mechanical detection, and belongs to the technical field of micro-electro-mechanical sensors. According to the basic working principle, a single-axis multi-mode resonance subsystem is designed and comprises a plurality of mass blocks and elastic beams, displacement caused by single-axis acceleration is synchronously detected through quasi-static and multi-order vibration modes, and a multi-mode filter is designed to achieve weight distribution of displacement detection quantities of all orders; the final displacement, caused by the acceleration, of the mass block is obtained through weighted fusion, the displacement can directly represent the acceleration in the open loop, and the feedback control voltage enabling the displacement to be constant in the closed loop can represent the acceleration. According to the invention, common-mode errors and temperature drift can be effectively suppressed, and the bandwidth can be expanded.

Description

Technical Field

[0001] The present invention belongs to the technical field of acceleration sensors, and more specifically, relates to an acceleration measurement method based on multi-modal micromechanical detection. Background Art

[0002] Accelerometers usually include two methods: displacement detection and frequency detection. They usually measure the quasi-static displacement change caused by uniaxial acceleration or the frequency change of the resonant subsystem. Correspondingly, capacitive micromechanical accelerometers are also divided into quasi-static accelerometers and resonant accelerometers, each of which has its own advantages and disadvantages. For example, the former has high sensitivity but limited bandwidth, and the latter has a large dynamic range but low sensitivity. Since the two accelerometers work in quasi-static and resonant states respectively, integrating the two detection methods on a single sensitive element will inevitably affect each other, making it difficult to achieve complementary advantages and disadvantages. Summary of the invention

[0003] In view of the shortcomings and deficiencies of existing micromechanical accelerometers, the present invention provides an acceleration measurement method based on multi-modal micromechanical detection, by constructing a multi-modal micromechanical resonator system, including multiple micro-mass blocks and micro-elastic beams, using the multi-order modes of the multi-modal micromechanical resonator system to synchronously measure the displacement, and realizing high-precision and high-bandwidth acceleration measurement through a filtering fusion method. In the traditional working mode (quasi-static), due to the large stiffness of the elastic beams between the multiple mass blocks, the same displacement is generated synchronously, which can be expressed by measuring the displacement of one of the main mass blocks through a capacitance detection method;

[0004] In the high-order vibration mode, the main mass block generates high-order vibration under the action of the variable spacing type driver. The vibration amount is positively correlated with the displacement of the main mass block. The displacement of the main mass block can be synchronously measured by demodulating the vibration amount.

[0005] When working in open loop, the multi-modal displacements tested synchronously are processed by designing a multi-modal filter, that is, different weights are assigned according to the acceleration frequency information, and the displacement information is weighted to achieve data fusion to characterize the acceleration magnitude.

[0006] When working in a closed loop, the feedback control voltage is calculated by comparing the fused displacement with the reference displacement through the controller and applied to the variable area actuator to generate a balancing force, so that the displacement is fixed at a set position, such as the zero position.

[0007] The technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a multi-mode micromechanical resonator system, comprising a multi-mode mass-spring system and a capacitor moving along a single axis direction, which are composed of a plurality of mass blocks and elastic beams, wherein the plurality of mass blocks are connected to each other through a large-rigidity elastic beam, and the plurality of mass blocks are each connected to an anchor region through a small-rigidity elastic beam;

[0009] Mobile comb-tooth electrodes are distributed on a main mass block among the multiple mass blocks, including a first mobile comb-tooth electrode arranged on the left and right sides of the main mass block, and a second mobile comb-tooth electrode, a third mobile comb-tooth electrode, and a fourth mobile comb-tooth electrode arranged on the upper and lower sides of the main mass block; the direction of the first mobile comb-tooth electrode is the same as the movement direction of the main mass block, and the directions of the second mobile comb-tooth electrode, the third mobile comb-tooth electrode, and the fourth mobile comb-tooth electrode are perpendicular to the movement direction of the main mass block;

[0010] The first movable comb-tooth electrode on the left and the fixed comb-tooth electrode fixed in the left anchor area of ​​the main mass block form a first variable-area driver; the first movable comb-tooth electrode on the right and the fixed comb-tooth electrode fixed in the right anchor area of ​​the main mass block form a second variable-area driver; the second movable comb-tooth electrode, the third movable comb-tooth electrode and the fourth movable comb-tooth electrode on the upper and lower sides respectively form a first variable-pitch capacitor, a variable-pitch driver and a second variable-pitch capacitor with the corresponding fixed comb-tooth electrodes fixed in the upper and lower anchor areas of the main mass block.

[0011] As a preferred embodiment of the present invention, the large-rigidity elastic beam and the small-rigidity elastic beam are arranged in parallel along the uniaxial motion direction, and the rigidity of the large-rigidity elastic beam is much greater than the rigidity of the small-rigidity elastic beam.

[0012] As a preferred embodiment of the present invention, the variable pitch driver is a differential structure, which is used to drive the main mass block to generate high-order resonance and electrostatic negative stiffness.

[0013] In a second aspect, the present invention provides an acceleration measurement method based on multi-modal micromechanical detection, which is implemented by the above-mentioned multi-modal micromechanical resonator system. When the multi-modal micromechanical resonator system is subjected to an acceleration lower than the fundamental frequency, multiple mass blocks synchronously generate approximate displacements, and open-loop and closed-loop acceleration detection are respectively implemented by detecting the displacement of the main mass block or maintaining the constant position of the main mass block, wherein the feedback control voltage of the closed-loop acceleration detection is applied to the first variable area driver and the second variable area driver;

[0014] The multi-modal micromechanical resonator system generates a high-order vibration mode under high-frequency excitation. In the high-order vibration mode, the vibration amplitude of the main mass block is positively correlated with the displacement of the main mass block. The displacement of the main mass block is synchronously measured by demodulating the vibration amplitude.

[0015] Furthermore, the relationship between the vibration amplitude of the main mass block and the displacement of the main mass block is as follows:

[0016]

[0017] Where δ is the vibration amplitude of the main mass block, x is the displacement of the main mass block, μ and Q are the variable spacing type actuator constant and quality factor, respectively, and k m is the m-order modal elastic coefficient, V d V is the DC component of the excitation signal applied by the variable pitch driver. a It is the AC component of the excitation signal applied to the variable pitch driver.

[0018] Furthermore, the open-loop acceleration detection method includes:

[0019] A carrier signal with opposite phases is applied to the first variable spacing capacitor and the second variable spacing capacitor, and a high-order modal resonance excitation signal is applied to the variable spacing driver; the signal on the mass block passes through the CV circuit and carrier demodulation in turn, and the demodulated carrier signal generates a quasi-static displacement signal through a low-pass filter, and at the same time, the demodulated carrier signal is subjected to high-order secondary demodulation and then passes through a bandpass filter corresponding to the high-order mode to generate a high-order modal displacement signal, and the displacement signals of each order modal after filtering by the multi-modal filter are fused as the final displacement signal, and the final displacement signal represents the magnitude of acceleration.

[0020] Furthermore, the closed-loop acceleration detection method includes:

[0021] The controller calculates a feedback control voltage based on the difference between the final displacement signal obtained by open-loop acceleration detection and the reference displacement signal, and applies it to the first variable area driver and the second variable area driver on the left and right sides of the main mass block to generate a balancing force, so that the mass block is fixed at a preset reference position. The feedback control voltage represents the magnitude of acceleration.

[0022] Furthermore, the power weighting method is used to fuse the filtered modal displacement signals of each order, specifically:

[0023] The square sum of the displacement signals of each order mode after filtering by the multimodal filter is calculated, and then the square root is calculated to obtain the final displacement signal.

[0024] Furthermore, the multi-modal filter comprises a low-pass filter whose base frequency is the cut-off frequency and a band-pass filter corresponding to the frequency range of the high-order vibration mode;

[0025] The cutoff frequency of the low-pass filter is the same as the first cutoff frequency of the band-pass filter corresponding to the second-order mode, the first cutoff frequency of the band-pass filter corresponding to the m-1-order mode is the same as the second cutoff frequency of the band-pass filter corresponding to the m-1-order mode, and the second cutoff frequency of the band-pass filter corresponding to the m-order mode is the same as the first cutoff frequency of the band-pass filter corresponding to the m+1-order mode, and m≥3.

[0026] In general, the technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

[0027] (1) The present invention, through the driving and structural design of the multi-modal micromechanical resonator system, can not only be used for traditional acceleration open-loop and closed-loop measurement methods, but also can realize multi-modal working mode, and has the advantages of simple structure, high integration, miniaturization, etc.

[0028] (2) The present invention can not only improve the acceleration detection accuracy but also broaden the acceleration detection bandwidth through synchronous detection and data fusion of multi-modal displacement, thereby achieving higher acceleration measurement performance.

[0029] (3) The present invention can simultaneously apply force balance closed-loop control and electrostatic adjustment technology to improve the linearity and accuracy of the micromechanical accelerometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic structural diagram of a two-mode micromechanical resonator system shown in an embodiment of the present invention;

[0031] Figure 2 It is a schematic diagram of the first-order vibration mode (quasi-static) of a two-mode micromechanical resonator system;

[0032] Figure 3 It is a schematic diagram of the second-order vibration mode of a two-mode micromechanical resonator system;

[0033] Figure 4 It is a schematic diagram of the framework of displacement detection, fusion and closed-loop method based on a two-mode micromechanical resonator system;

[0034] In all the drawings, the same figure marks are used to represent the same structure, wherein: 1-first small stiffness elastic beam, 2-main mass block, 3-large stiffness elastic beam, 4-second mass block, 5-second small stiffness elastic beam, 6-first variable area type driver, 7-first variable spacing type capacitor, 8-variable spacing type driver, 9-second variable spacing type capacitor, 10-second variable area type driver. DETAILED DESCRIPTION

[0035] In order to more clearly express the purpose, technical solutions and advantages of the present invention, further explanation is given below in conjunction with the accompanying drawings and formula derivations. It should be understood that the principles herein are used to explain the present invention, but are not limited to the present invention.

[0036] The invention is based on a multi-mode micromechanical resonator, and its structure includes a movable micro-mass block, a micro-elastic beam with different stiffness, a variable-pitch displacement detection capacitor, a variable-pitch driver and a variable-area driver. Figure 1It is a schematic diagram of the structure of a typical two-mode micromechanical resonator system in an embodiment of the present invention, including a first small-rigidity elastic beam 1, a main mass block 2, a large-rigidity elastic beam 3, a second mass block 4, a second small-rigidity elastic beam 5, a variable-area driver 6, a variable-spacing capacitor 7, a variable-spacing driver 8, a variable-spacing capacitor 9, and a variable-area driver 10.

[0037] The elastic beam and the mass block constitute a two-mode mass-spring system moving along the X direction, wherein the main mass block and the second mass block are rigid structures, connected together by a large-rigidity elastic beam 3, and connected to the anchor area structure by their own small-rigidity elastic beams. The fundamental resonance frequency is determined by the elastic beam with smaller stiffness and the mass block, and the high-order resonance frequency is determined by the elastic beam with larger stiffness and the mass block. Comb-tooth electrodes are distributed on the structure of the main mass block 2, including the first movable comb-tooth electrodes arranged on the left and right sides of the main mass block, and the second movable comb-tooth electrodes, the third movable comb-tooth electrodes, and the fourth movable comb-tooth electrodes arranged on the upper and lower sides of the main mass block. According to their functional distinction, the first movable comb-tooth electrode is a variable-area drive electrode, the second movable comb-tooth electrode and the fourth movable comb-tooth electrode are variable-pitch displacement detection electrodes, and the third movable comb-tooth electrode is a variable-pitch drive electrode. The above-mentioned movable comb-tooth electrodes and the corresponding fixed comb-tooth electrodes distributed on the anchor area respectively constitute a variable-area driver 6, a variable-pitch capacitor 7, a variable-pitch row driver 8, a variable-pitch capacitor 9, and a variable-area driver 10.

[0038] like Figure 4 As shown, when the micromechanical resonator is subjected to an acceleration lower than the fundamental frequency, the two mass blocks synchronously generate approximately the same quasi-static displacement. By applying carrier signals with opposite phases to the variable-spacing capacitors 7 and 9 on the main mass block, and extracting the response signal on the mass block through the C / V detection circuit, the displacement of the mass block movement can be detected, and the displacement can be defined as the quasi-static modal detection displacement; at the same time, by applying the second-order modal vibration excitation signal to the variable-spacing driver 8 on the main mass block 2, since the electrode on the main mass block generates a displacement that deviates from the center position of the variable-spacing driver 8, the driver generates a resonant driving force that can cause the second-order modal vibration, and the magnitude of the resonant driving force is positively correlated with the distance of the main mass block from the center of the differential electrode. By extracting the response signal on the mass block, the displacement that deviates from the center position can be detected through carrier demodulation, secondary demodulation and bandpass filtering, and the detection displacement can be defined as the second-order modal detection displacement; the second-order modal detection displacement is zero, that is, when the main mass block is located at the center position of the variable-spacing driver, the second-order modal driving force and the response are both zero. Figure 2 and Figure 3 The first-order vibration mode (quasi-static) and second-order vibration mode of a two-mode micromechanical resonator system are shown.

[0039] The quasi-static modal detection displacement and the second-order modal detection displacement are processed by a low-pass filter and a band-pass filter after demodulation. On the one hand, high-frequency signals related to the carrier and the second-order excitation are filtered out, and on the other hand, weight processing can be introduced for the two detection displacements in the frequency range. After power weighting, displacement information fused according to frequency characteristics can be obtained, that is, the weight of the quasi-static detection displacement in the low-frequency band is higher than the weight of the second-order detection displacement, and the weight of the quasi-static detection displacement in the high-frequency band is lower than the weight of the second-order detection displacement; the cutoff frequency of the low-pass filter is the same as the first cutoff frequency of the band-pass filter, and the second cutoff frequency of the band-pass filter determines the open-loop acceleration measurement bandwidth; the fusion method fully takes into account the high sensitivity of the quasi-static detection displacement method and the high bandwidth characteristics of the second-order detection displacement.

[0040] The multi-modal displacement measurement of the present invention is to obtain the magnitude of each order of vibration by demodulating the response signal on the detection capacitor to satisfy the expression Where δ, μ, Q, k m ,V d ,V a , x are the vibration amplitude of the m-order mode, the driver constant, the quality factor, the elastic coefficient, the DC component and the AC component of the excitation signal applied by the variable pitch driver, and the displacement.

[0041] The closed-loop working mode of acceleration measurement is to compare the fused displacement with the set value, calculate the feedback control voltage through the controller, and apply it to the variable area drivers 6 and 10, so as to maintain the constant vibration amount, that is, the displacement of the main mass under the action of acceleration is constant. One typical closed-loop set value is zero, at this time the quasi-static displacement of the resonator is zero and the second-order vibration is zero.

[0042] The variable pitch driver 8 is a differential structure, which can drive the main mass block to generate second-order resonance and generate electrostatic negative stiffness, thereby reducing the fundamental frequency of the resonator and improving the sensitivity of quasi-static detection.

[0043] In addition to the two-mode micromechanical resonator system shown in the above embodiment, other high-order forms can also be used, which need to meet the requirements of a multi-mode mass-spring system and a driver moving along a single axis direction composed of multiple mass blocks and elastic beams, the multiple mass blocks are connected by large-rigidity elastic beams, and the multiple mass blocks are each connected to the anchor area by a small-rigidity elastic beam; a variable-area driver 6, a variable-spacing capacitor 7, a variable-spacing driver 8 and a variable-spacing capacitor 9 are distributed on one of the main mass blocks.

[0044] The displacement signals of each order modal after fusion multimodal filter filtering are used as the final displacement signal, and the final displacement signal represents the magnitude of acceleration. The multimodal filter comprises a low-pass filter with the base frequency as the cut-off frequency and a band-pass filter corresponding to the frequency range of the high-order vibration mode.

[0045] The cutoff frequencies of the low-pass filter and the band-pass filter corresponding to the second-order mode are the same, and the cutoff frequencies of the band-pass filters corresponding to the second-order and higher-order modes satisfy the following relationship: the first cutoff frequency of the band-pass filter corresponding to the m-order mode is the same as the second cutoff frequency of the band-pass filter corresponding to the m-1-order mode, and the second cutoff frequency of the band-pass filter corresponding to the m-order mode is the same as the first cutoff frequency of the band-pass filter corresponding to the m+1-order mode.

[0046] When fusing the displacement signals of each order of modal after filtering by the multimodal filter, the power weighting method is used. After each order of modal displacement is processed by the corresponding filter, the square sum of each order of modal displacement after filtering is calculated, and then the square root is calculated to obtain the final displacement.

[0047] The present invention designs a uniaxial multi-modal resonator system, uses multi-order vibration modes to synchronously detect the displacement caused by uniaxial acceleration, and designs filters to achieve weight distribution of each order of displacement detection. The final displacement of the mass block caused by acceleration is obtained by weighted fusion. When the loop is open, the displacement can directly characterize the magnitude of acceleration. When the loop is closed, the feedback control voltage that makes the displacement constant can characterize the magnitude of acceleration. The invention can effectively suppress common mode error, temperature drift and expand bandwidth.

[0048] Those skilled in the art should understand 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 multi-mode micromechanical resonator system, characterized in that: A multi-mode mass-spring system and a capacitor moving along a single axis direction, comprising a plurality of mass blocks and elastic beams, wherein the plurality of mass blocks are connected to each other through a large-rigidity elastic beam, and the plurality of mass blocks are each connected to an anchoring area through a small-rigidity elastic beam; Mobile comb-tooth electrodes are distributed on a main mass block among the multiple mass blocks, including a first mobile comb-tooth electrode arranged on the left and right sides of the main mass block, and a second mobile comb-tooth electrode, a third mobile comb-tooth electrode, and a fourth mobile comb-tooth electrode arranged on the upper and lower sides of the main mass block; the direction of the first mobile comb-tooth electrode is the same as the movement direction of the main mass block, and the directions of the second mobile comb-tooth electrode, the third mobile comb-tooth electrode, and the fourth mobile comb-tooth electrode are perpendicular to the movement direction of the main mass block; The first movable comb-tooth electrode on the left side and the fixed comb-tooth electrode fixed on the left anchor area of ​​the main mass block form a first variable area driver (6); the first movable comb-tooth electrode on the right side and the fixed comb-tooth electrode fixed on the right anchor area of ​​the main mass block form a second variable area driver (10); the second movable comb-tooth electrode, the third movable comb-tooth electrode and the fourth movable comb-tooth electrode on the upper and lower sides respectively form a first variable pitch capacitor (7), a variable pitch driver (8) and a second variable pitch capacitor (9) with the corresponding fixed comb-tooth electrodes fixed on the upper and lower anchor areas of the main mass block.

2. The multi-mode micromechanical resonator system according to claim 1, characterized in that: The large-rigidity elastic beam and the small-rigidity elastic beam are arranged in parallel along the uniaxial motion direction, and the rigidity of the large-rigidity elastic beam is much greater than that of the small-rigidity elastic beam.

3. The multi-mode micromechanical resonator system according to claim 1, characterized in that: The variable pitch driver (8) is a differential structure, and is used to drive the main mass block to generate high-order resonance and electrostatic negative stiffness.

4. An acceleration measurement method based on multi-modal micromechanical detection, implemented by the multi-modal micromechanical resonator system according to claim 1, characterized in that: When the multi-modal micromechanical resonator system is subjected to an acceleration lower than the fundamental frequency, multiple mass blocks synchronously generate approximate displacements, and open-loop and closed-loop acceleration detections are respectively realized by detecting the displacement of the main mass block or maintaining the position of the main mass block constant, wherein the feedback control voltage of the closed-loop acceleration detection is applied to the first variable area driver (6) and the second variable area driver (10); The multi-modal micromechanical resonator system generates a high-order vibration mode under high-frequency excitation. In the high-order vibration mode, the vibration amplitude of the main mass block is positively correlated with the displacement of the main mass block. The displacement of the main mass block is synchronously measured by demodulating the vibration amplitude.

5. The acceleration measurement method based on multimodal micromechanical detection according to claim 4, characterized in that: The relationship between the vibration amplitude of the main mass block and the displacement of the main mass block is as follows: Where δ is the vibration amplitude of the main mass block, x is the displacement of the main mass block, μ and Q are the variable spacing type actuator constant and quality factor, respectively, and k m is the m-order modal elastic coefficient, V d V is the DC component of the excitation signal applied by the variable pitch driver. a It is the AC component of the excitation signal applied to the variable pitch driver.

6. The acceleration measurement method based on multimodal micromechanical detection according to claim 4, characterized in that: Open-loop acceleration detection methods include: Carrier signals with opposite phases are applied to the first variable pitch capacitor (7) and the second variable pitch capacitor (9), and a high-order modal resonance excitation signal is applied to the variable pitch driver (8); the signal on the mass block passes through a CV circuit and carrier demodulation in sequence, the demodulated carrier signal is low-pass filtered to generate a quasi-static displacement signal, and the demodulated carrier signal is high-order secondary demodulated and then passed through a bandpass filter corresponding to the high-order mode to generate a high-order modal displacement signal, and the displacement signals of each order modal filtered by a multi-modal filter are merged as a final displacement signal, wherein the final displacement signal represents the magnitude of acceleration.

7. The acceleration measurement method based on multimodal micromechanical detection according to claim 6, characterized in that: Closed-loop acceleration detection methods include: The controller calculates a feedback control voltage based on the difference between a final displacement signal obtained by open-loop acceleration detection and a reference displacement signal, and applies the feedback control voltage to a first variable area driver (6) and a second variable area driver (10) on the left and right sides of the main mass block to generate a balancing force, thereby fixing the mass block at a preset reference position, wherein the feedback control voltage represents the magnitude of acceleration.

8. The acceleration measurement method based on multi-modal micromechanical detection according to claim 6, characterized in that: The power weighted method is used to fuse the filtered displacement signals of each order modal, specifically: The square sum of the displacement signals of each order mode after filtering by the multimodal filter is calculated, and then the square root is calculated to obtain the final displacement signal.

9. The acceleration measurement method based on multi-modal micromechanical detection according to claim 6, characterized in that: The multi-modal filter comprises a low-pass filter whose base frequency is the cut-off frequency and a band-pass filter corresponding to the frequency range of the high-order vibration mode; The cutoff frequency of the low-pass filter is the same as the first cutoff frequency of the band-pass filter corresponding to the second-order mode, the first cutoff frequency of the band-pass filter corresponding to the m-1-order mode is the same as the second cutoff frequency of the band-pass filter corresponding to the m-1-order mode, and the second cutoff frequency of the band-pass filter corresponding to the m-order mode is the same as the first cutoff frequency of the band-pass filter corresponding to the m+1-order mode, and m≥3.

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