A three-axis micromechanical accelerometer and its control method

Abstract

The present invention discloses a three-axis micromechanical accelerometer and a control method thereof, which belong to the field of acceleration measurement technology, including XY two-axis linear acceleration and Z-axis angular acceleration measurement. Through a single mass block and an L-shaped elastic beam, it is ensured that the first three vibration modes of the accelerometer are respectively the above-mentioned three-axis sensitive motions. Based on the comb-tooth capacitor combination design, a closed-loop three-axis accelerometer control method is proposed, including an XY linear stiffness adjustment method, an XY linear displacement and Z angle detection method, a two-axis force balance and a one-axis torque balance method. The force and torque balance voltage is calculated by a PID controller and applied to the drive electrode in a push-pull manner to realize closed-loop three-axis accelerometer control. The present invention adopts a single mass block and a distributed comb structure design, which has a simple structure and a simple accelerometer control method. It also integrates an equivalent stiffness adjustment method, which helps to improve the miniaturization, integration and accuracy of the three-axis accelerometer.

Description

Technical Field

[0001] The present invention belongs to the technical field of acceleration measurement, and more particularly, relates to a micromechanical accelerometer and a control method thereof. Background Art

[0002] Electrostatically suspended accelerometers utilize an electrostatic force balance method to simultaneously measure acceleration along six axes. While highly accurate, electrostatically suspended accelerometers are difficult to manufacture, hindering mass production and further expansion. Electrostatically suspended microaccelerometers utilizing MEMS processing technology, while offering the advantages of mass production, still face challenges with complex processing, control, and detection systems, and are still in the basic research phase. Currently, the more mature capacitive three-axis microaccelerometers typically utilize a multi-mass block structure. While this facilitates motion decoupling along the three axes, it suffers from low accuracy. Summary of the Invention

[0003] In response to the shortcomings and deficiencies of existing three-axis micromechanical accelerometers, the present invention provides a three-axis micromechanical accelerometer and a control method thereof. A single mass block and an L-shaped elastic beam are used to realize X-axis linear sensing, Y-axis linear sensing, and Z-axis rotation sensing. By designing comb capacitors and their combination forms, an electrostatic adjustment unit, a linear displacement detection unit, an angle detection unit, a force balance unit, and a torque balance unit are deployed. Not only does a closed-loop control method realize three-axis acceleration closed-loop detection, but the electrostatic adjustment method can also be used to adjust the equivalent stiffness of the accelerometer in the X-axis and Y-axis to zero, thereby improving the detection accuracy of the accelerometer. The accelerometer and the control method thereof are simpler and more practical.

[0004] The technical solution adopted in the present invention is as follows:

[0005] In a first aspect, the present invention provides a three-axis micro-machined accelerometer, comprising an acceleration sensitive element, an electrostatic adjustment unit, a linear displacement detection unit, a rotation angle detection unit, a force balance unit, and a torque balance unit;

[0006] The acceleration sensitive element includes a single mass block and an elastic beam. The elastic beam is an L-shaped structure and has linear stiffness in the directions of X-axis linear motion, Y-axis linear motion, and Z-axis rotational motion. The single mass block is composed of a plurality of distributed mass structures combined by a rigid connecting arm, connected to the movable comb teeth, symmetrically distributed, and connected to the anchor area via the L-shaped elastic beam, wherein one end of the L-shaped elastic beam is connected to the anchor area, and the other end is connected to the single mass block. Preferably, the distance between the connection point of the elastic beam on the anchor area and the center of the single mass block is less than the distance between the connection point of the elastic beam on the connecting arm and the center of the single mass block. The connecting arm of the single mass block is provided with multiple groups of fixed comb teeth.

[0007] The electrostatic adjustment unit includes an electrostatic adjustment electrode and corresponding electrostatic adjustment comb teeth. The electrostatic adjustment comb teeth and a first set of fixed comb teeth on the connecting arm form an electrostatic adjustment capacitor. The X-direction electrostatic adjustment capacitor generates an electrostatic negative stiffness in the X-axis direction under the action of the X-direction electrostatic adjustment voltage. The Y-direction electrostatic adjustment capacitor generates an electrostatic negative stiffness in the Y-axis direction under the action of the Y-direction electrostatic adjustment voltage. The electrostatic force generated by the electrostatic adjustment unit in the X-axis and Y-axis directions is zero. In the electrostatic adjustment capacitor combination, the electrostatic adjustment electrodes corresponding to each set of electrostatic adjustment capacitors can be applied with the same or different electrostatic adjustment voltages, and can be adjusted according to the requirement of zero electrostatic force.

[0008] The linear displacement detection unit includes a detection electrode and its corresponding detection comb teeth. The detection comb teeth and the third set of fixed comb teeth on the connecting arm form a detection capacitor for realizing X-axis and Y-axis linear displacement detection;

[0009] The rotation angle detection unit and the linear displacement detection unit share the detection electrode and detection capacitor to realize Z-axis rotation angle detection; the present invention uses different combinations of the same comb-tooth capacitor to realize linear displacement detection and rotation angle detection;

[0010] The force balancing unit includes a force driving electrode and its corresponding force driving comb teeth, and the force driving comb teeth and the second set of fixed comb teeth on the connecting arm form a force driving capacitor;

[0011] The torque balancing unit includes a torque driving electrode and its corresponding torque driving comb teeth. The torque driving comb teeth and the fourth group of fixed comb teeth on the connecting arm form a torque driving capacitor.

[0012] Furthermore, the first group of fixed comb teeth, the second group of fixed comb teeth, the third group of fixed comb teeth, and the fourth group of fixed comb teeth are evenly arranged in sequence from the center of the single mass block to the outside along the connecting arm, forming a centrally symmetrical structure.

[0013] Furthermore, in the linear displacement detection unit, when the mass block moves along the X-axis and the Y-axis, the detection capacitances of the decrease and increase of the capacitance gap are differential with each other, that is, the detection capacitance in the positive direction of the X-axis and the detection capacitance in the negative direction of the X-axis are mutually X-axis detection differential capacitances, and the detection capacitance in the positive direction of the Y-axis and the detection capacitance in the negative direction of the Y-axis are mutually Y-axis detection differential capacitances. By applying a carrier voltage to the detection electrode, carrier modulation of the capacitance change signal caused by the variable gap is realized. The signal on the detection electrode becomes a digital displacement signal after passing through the CV circuit, differential processing, AD conversion circuit, multiplication demodulation and low-pass filtering signal processing.

[0014] Furthermore, in the angle detection unit, when the single mass block rotates clockwise around the Z-axis, the detection capacitances with increased and decreased overlapping areas serve as Z-axis detection differential capacitances. By applying a carrier voltage to the detection electrode, carrier modulation of the capacitance change signal caused by the variable area is achieved. The signal on the detection electrode becomes a digital angle signal after undergoing CV circuit, differential processing, AD conversion circuit, multiplication demodulation and low-pass filtering signal processing.

[0015] Furthermore, in the force balancing unit, the combination method is consistent with that of the linear displacement detection unit. The force driving capacitor in the positive direction of the X-axis and the force driving capacitor in the negative direction of the X-axis are mutually X-axis driving differential capacitors, and the force driving capacitor in the positive direction of the Y-axis and the force driving capacitor in the negative direction of the Y-axis are mutually Y-axis driving differential capacitors. The force balancing voltage is calculated based on the displacement signal detected by the linear displacement detection unit, and is applied to the force driving electrode after passing through the push-pull circuit to generate an electrostatic force, so that the single mass block works in the reference position.

[0016] Furthermore, in the torque balancing unit, the combination method is consistent with the angle detection unit, that is, they appear alternately in the clockwise direction. When the single mass block rotates clockwise around the Z-axis, the torque driving capacitor with increasing and decreasing overlapping area is the Z-axis torque driving differential capacitor. The torque balancing voltage is calculated based on the angle signal detected by the angle detection unit, and is applied to the torque driving electrode after passing through the push-pull circuit to generate an electrostatic torque, so that the single mass block operates at the reference angle.

[0017] In the present invention, the force balancing unit and the torque balancing unit use independent driving capacitors, and the driving electrodes corresponding to each set of driving capacitors independently apply voltage signals.

[0018] Furthermore, the electrostatic adjustment capacitor, detection capacitor, force-driven capacitor and torque-driven capacitor contain multiple pairs of comb tooth structures, each fixed comb tooth is adjacent to two movable comb teeth, forming two pairs of capacitors with different gaps, and the gap satisfies d2>3d1, where d1 represents the gap between the fixed comb tooth and the first adjacent movable comb tooth, and d2 represents the gap between the fixed comb tooth and the second adjacent movable comb tooth.

[0019] In a second aspect, the present invention provides a control method for the above-mentioned three-axis micromachined accelerometer, which positions the mass block at a reference position / angle through a force / torque balance method, and simultaneously reduces its equivalent stiffness to a preset value by applying electrostatic negative stiffness on the X and Y axes, comprising the following steps:

[0020] Step 1: When the mass block is subjected to external acceleration, carrier modulation is achieved by applying a carrier voltage to the detection electrodes in the linear displacement detection unit and the rotation angle detection unit to generate the capacitance change signal caused by the variable gap and the capacitance change signal caused by the variable area. The signals on the detection electrodes are processed by a CV circuit, differential processing, an AD conversion circuit, multiplication demodulation, and low-pass filtering to obtain digital displacement signals and digital rotation angle signals, respectively.

[0021] Step 2: The digital displacement signal and the digital rotation angle signal are respectively calculated by different PID controllers to obtain the X-axis force balance voltage V FX , Y-axis force balance voltage V FY and Z-axis torque balance voltage V FZ ;

[0022] Through the push-pull circuit, a voltage V is applied to the force driving electrodes corresponding to the X-axis driving differential capacitor. FX +V DC1 and V FX -V DC1 , apply voltage V to the force driving electrodes corresponding to the Y-axis driving differential capacitor FY +V DC2 and V FY -V DC2 , so that the mass block works at the reference position on the XY plane; where V DC1 and V DC2 are the DC bias voltages for the X-axis and Y-axis respectively;

[0023] Through the push-pull circuit, a voltage V is applied to the torque driving electrodes corresponding to the Z-axis detection differential capacitance. FZ +V DC3 and V FZ -V DC3 , so that the mass block works at the Z-axis reference angle; where V DC3 is the Z-axis DC bias voltage;

[0024] Furthermore, the electrostatic force generated by the force balance voltage on the X-axis and the Y-axis is expressed as:

[0025]

[0026]

[0027] Where ε is the dielectric constant, N FX and N FY The number of comb teeth in the force-driven capacitance of the X-axis and Y-axis, S FX and S FY The overlapping area of the comb teeth in the force-driven capacitance of the X-axis and Y-axis, d FX and d FYThe gaps between the teeth of the force-driven capacitors for the X and Y axes, F X and F Y are the electrostatic forces generated along the X and Y axes respectively;

[0028] The electrostatic torque generated by the torque balancing voltage on the Z axis is expressed as:

[0029]

[0030] Where ε is the dielectric constant, N FZ is the number of teeth in the torque drive capacitor, L FZ is the distance between the torque-driven comb capacitor and the center of the mass block, h FZ is the thickness of the torque-driven comb teeth, d FZ1 and d FZ2 is the gap between the teeth of the torque-driven comb capacitor, F Z is the electrostatic torque generated on the Z axis.

[0031] Step 3: Use the X-axis force balance voltage, Y-axis force balance voltage, and Z-axis moment balance voltage to calculate the X-axis electrostatic negative stiffness and Y-axis electrostatic negative stiffness generated by the electrostatic force and electrostatic moment, respectively. By comparing them with the equivalent stiffness preset values, the X-axis electrostatic adjustment voltage and Y-axis electrostatic adjustment voltage are calculated and applied to the electrostatic drive electrode through the amplification circuit, thereby keeping the X-axis equivalent stiffness and Y-axis equivalent stiffness constant.

[0032] Furthermore, the X-axis force balance voltage, X-axis electrostatic adjustment voltage, X-axis DC bias voltage, Y-axis force balance voltage, Y-axis electrostatic adjustment voltage, Y-axis DC bias voltage, Z-axis moment balance voltage, and Z-axis DC bias voltage are squared, multiplied by a fixed gain, and then added according to the following expression to obtain the X-axis total electrostatic negative stiffness and the Y-axis total electrostatic negative stiffness.

[0033]

[0034]

[0035] Where ε is the dielectric constant, N TX and N TY are the comb teeth logarithms of the electrostatic trimming capacitors on the X and Y axes, S TX and S TY are the overlapping areas of the electrostatic trimming capacitors on the X and Y axes, respectively, and d TX and d TY are the comb gaps in the electrostatic trimming capacitors for the X and Y axes, respectively, and K X and K Y The total electrostatic negative stiffness generated for the X and Y axes respectively.

[0036] In general, the technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

[0037] (1) The present invention utilizes a single mass block and an L-shaped elastic beam to simultaneously realize three-axis acceleration detection, which has the advantages of simple processing technology, high integration, and miniaturization.

[0038] (2) The present invention simultaneously applies force balance closed-loop control and electrostatic adjustment technology to improve the linearity and accuracy of the micromechanical accelerometer. The proposed force balance and equivalent stiffness control method is easy to implement in a digital controller.

[0039] (3) The micro-mechanical accelerometer of the present invention does not rely on the difficult silicon processing technology, and can simply achieve a preset low equivalent stiffness or even a quasi-zero equivalent stiffness by using only electrostatic adjustment technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 1 is a schematic structural diagram of a three-axis micromachined accelerometer provided by an embodiment of the present invention;

[0041] Figure 2 Schematic diagram of the comb structure of a micromechanical accelerometer provided in an embodiment of the present invention;

[0042] Figure 3 This is a schematic diagram of the control flow of the electrostatic adjustment unit of the three-axis micromachined accelerometer of the present invention;

[0043] Figure 4 This is a schematic diagram of the XY two-axis linear displacement detection and force balance control process of the three-axis micro-mechanical accelerometer in the present invention;

[0044] Figure 5 This is a schematic diagram of the Z-axis angle detection and torque balance control process of the three-axis micro-machined accelerometer in the present invention;

[0045] In all the drawings, the same reference numerals are used to denote the same structures, wherein: 1-anchor region, 2-elastic beam, 3-mass block, 4-torque driving electrode MX2, 5-detection electrode CX2, 6-force driving electrode FX2, 7-electrostatic adjustment electrode TX2, 8-electrostatic adjustment electrode TX3, 9-force driving electrode FX3, 10-detection electrode CX3, 11-torque driving electrode MX3, 12-torque driving electrode MY1, 13-detection electrode CY1, 14-force driving electrode FY1, 15-electrostatic adjustment electrode TY1, 16-electrostatic adjustment electrode TY4, 17-force driving electrode FY4, 18-detection electrode CY4, 19-torque driving Electrode MY4, 20-torque driving electrode MY2, 21-detection electrode CY2, 22-force driving electrode FY2, 23-electrostatic adjustment electrode TY2, 24-electrostatic adjustment electrode TY3, 25-force driving electrode FY3, 26-detection electrode CY3, 27-torque driving electrode MY3, 28-torque driving electrode MX4, 29-detection electrode CX4, 30-force driving electrode FX4, 31-electrostatic adjustment electrode TX4, 32-electrostatic adjustment electrode TX1, 33-force driving electrode FX1, 34-detection electrode CX1, 35-torque driving electrode MX1, 36-fixed comb electrode, 37-fixed comb, 38-moving comb, V TX -X-axis electrostatic adjustment voltage, V TY -Y-axis electrostatic adjustment voltage, V FX -X-axis force balance voltage, V FY -Y-axis force balance voltage, V FZ -Z-axis torque balance voltage, V DC1 -X-axis DC bias voltage, V DC2 -Y-axis DC bias voltage, V DC3 -Z-axis DC bias voltage. DETAILED DESCRIPTION

[0046] In order to more clearly express the purpose, technical solutions and advantages of the present invention, the following is a further explanation with reference to 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.

[0047] The invention comprises structures such as a mass block, an elastic beam, a comb-tooth capacitor and an anchor area. Figure 1 This is a schematic diagram of the structure of a three-axis micromachined accelerometer provided by an embodiment of the present invention, comprising an anchor region 1, an elastic beam structure 2, a mass block 3, and a comb structure. The comb structure comprises, by function, an electrostatic adjustment unit, a linear displacement detection unit, a rotation angle detection unit, a force balance unit, and a torque balance unit.

[0048] The electrostatic adjustment unit includes an X-axis electrostatic adjustment unit and a Y-axis electrostatic adjustment unit. The X-axis electrostatic adjustment unit includes electrostatic adjustment electrodes 7, 8, 31, and 32 and their corresponding comb teeth; the Y-axis electrostatic adjustment unit includes electrostatic adjustment electrodes 15, 16, 23, and 24 and their corresponding comb teeth. Starting from the positive direction of the X-axis, the electrostatic adjustment electrodes on the X-axis are labeled TX1-TX4 in a counterclockwise direction; starting from the positive direction of the Y-axis, the electrostatic adjustment electrodes on the Y-axis are labeled TY1-TY4 in a counterclockwise direction. The comb teeth mounted on the electrostatic adjustment electrodes are called electrostatic adjustment comb teeth and are fixed comb teeth. The comb capacitance formed by the electrostatic adjustment comb teeth and the movable comb teeth on the mass block is called the electrostatic adjustment capacitance.

[0049] The linear displacement detection unit includes an X-axis displacement detection unit and a Y-axis displacement detection unit. The X-axis displacement detection unit includes detection electrodes 5 and 34 and their corresponding comb teeth, as well as differential detection electrodes 10 and 29 and their corresponding comb teeth. Starting from the positive direction of the X-axis and proceeding counterclockwise, the detection electrodes on the X-axis are sequentially designated as CX1-CX4. The Y-axis displacement detection unit includes detection electrode groups 13 and 21 and their corresponding comb teeth, as well as differential detection electrode groups 18 and 26 and their corresponding comb teeth. Starting from the positive direction of the Y-axis and proceeding counterclockwise, the detection electrodes on the Y-axis are sequentially designated as CY1-CY4. The comb teeth mounted on the detection electrodes are referred to as detection comb teeth and are fixed comb teeth. The comb capacitance formed by the detection comb teeth and the movable comb teeth on the mass is referred to as the detection capacitance.

[0050] The rotation angle detection unit is a Z-axis rotation angle detection unit, which includes detection electrodes 10, 13, 26, 34 and their corresponding comb teeth, and differential detection electrodes 5, 29, 18, 21 and their corresponding comb teeth.

[0051] The force balancing unit includes an X-axis force balancing unit and a Y-axis force balancing unit, and the torque balancing unit is a Z-axis torque balancing unit, wherein the X-axis force balancing unit includes force driving electrodes 6, 33 and their corresponding comb teeth, and differential force driving electrodes 9, 30 and their corresponding comb teeth. Starting from the positive direction of the X-axis, the force driving electrodes on the X-axis are sequentially recorded as FX1-FX4 in the counterclockwise direction; the Y-axis force balancing unit includes force driving electrodes 14, 22 and their corresponding comb teeth, and differential force driving electrodes 17, 25 and their corresponding comb teeth. Starting from the positive direction of the Y-axis, the force driving electrodes on the Y-axis are sequentially recorded as FY1-FY4 in the counterclockwise direction; the comb teeth installed on the force driving electrodes are called force driving comb teeth, which are fixed comb teeth, and the comb tooth capacitance formed by the force driving comb teeth and the movable comb teeth on the mass block is called force driving capacitance. The Z-axis torque balancing unit includes torque driving electrodes 4, 19, 20, 28 and their corresponding comb teeth, and differential torque driving electrodes 11, 12, 27, 35 and their corresponding comb teeth. Starting from the positive direction of the X-axis, the torque driving electrodes on the XY plane are recorded as MX1-MX2, MY1-MY2, MX3-MX4, and MY3-MY4 in the counterclockwise direction; the comb teeth installed on the torque driving electrodes are called torque driving comb teeth, which are fixed comb teeth, and the comb tooth capacitance formed by the torque driving comb teeth and the movable comb teeth on the mass block is called torque driving capacitance.

[0052] Combine Figure 1 and Figure 2 , wherein the electrostatic adjustment unit, linear displacement detection unit, force balance unit, and torque balance unit all use the same comb-tooth capacitor structure, and the linear displacement detection unit and the angle detection unit share a set of comb-tooth capacitor structures. The comb-tooth capacitor structure includes movable comb teeth 38 mounted on the mass 3 and fixed comb teeth 37 mounted on the electrode 36. Each set of comb-tooth capacitor structures contains multiple pairs of comb teeth, wherein each fixed comb tooth 37 is adjacent to two movable comb teeth 38, forming two pairs of capacitors with different gaps. The gap satisfies d2>3d1, where d1 represents the gap between the fixed comb tooth and the first movable comb tooth, and d2 represents the gap between the fixed comb tooth and the second movable comb tooth.

[0053] The single mass block 3 and the "L"-shaped elastic beam 2 constitute an acceleration sensitive element. The mass block 3 is connected to the anchor area 1 through the elastic beam 2. The elastic beam 2 has linear stiffness in the directions of X-axis linear motion, Y-axis linear motion and Z-axis rotational motion.

[0054] like Figure 3As shown, under the action of the bias voltage, the electrostatic adjustment electrodes TX1-TX4 on the X axis of the electrostatic adjustment unit generate a negative electrostatic stiffness in the X axis direction. Under the action of the bias voltage, the electrostatic adjustment electrodes TY1-TY4 on the Y axis of the electrostatic adjustment unit generate a negative electrostatic stiffness in the Y axis direction. The electrostatic force generated by the electrostatic adjustment unit in the X and Y axis directions is zero, and the electrostatic adjustment voltage V TX and V TY The size of the negative electrostatic stiffness is adjusted, where V TX is the X-axis electrostatic adjustment voltage, used to apply to TX1-TX4; V TY It is the Y-axis electrostatic adjustment voltage, used to be applied to TY1-TY4.

[0055] like Figure 4 As shown in the left half of the figure, the electrode groups CX1 and CX2 in the X-axis linear displacement detection unit are differential with the electrode groups CX3 and CX4, and the electrode groups CY1 and CY2 in the Y-axis linear displacement detection unit are differential with the electrode groups CY3 and CY4. By applying a carrier voltage to the moving comb teeth, carrier modulation of the capacitance change signal caused by the variable gap is achieved. After the signal on each detection electrode is processed by the CV circuit, A / D conversion circuit, multiplication demodulation and low-pass filtering signal, it becomes a digital displacement signal; the digital displacement signal is subjected to PID operation and D / A conversion to obtain a force balance voltage. In this embodiment, the capacitance change signal corresponding to the X-axis linear displacement is (C X1 +C X2 )-(C X3 +C X4 ), the capacitance change signal corresponding to the Y-axis linear displacement is (C Y1 +C Y2 )-(C Y3 +C Y4 ), where C X1 、C X2 、C X3 、C X4 、C Y1 、C Y2 、C Y3 、C Y4 They are the capacitance changes of the detection capacitors corresponding to CX1, CX2, CX3, CX4, CY1, CY2, CY3, and CY4 respectively.

[0056] The rotation angle detection unit and the linear displacement detection unit share the comb capacitor, such as Figure 5As shown in the left half of the figure, the electrode groups CX1, CX3, CY1, and CY3 in the angle detection unit are differential with the electrode groups CX2, CX4, CY2, and CY4. By applying a carrier voltage to the fixed comb teeth, carrier modulation of the capacitance change signal caused by the variable area is achieved. After the signals on each group of moving comb teeth are processed by the CV circuit, AD conversion circuit, multiplication demodulation, and low-pass filtering, they become digital angle signals; the digital angle signals are subjected to PID calculation and D / A conversion to obtain the torque balance voltage. In this embodiment, the capacitance change signal corresponding to the Z-axis angle is (C X1 +C X3 +C Y1 +C Y3 )-(C X2 +C X4 +C Y2 +C Y4 ).

[0057] In the control method of the micro accelerometer, the three-axis force / torque balance voltage is obtained respectively through three-way decoupled displacement detection and PID controller calculation, and the three-axis force / torque balance voltage is applied to the force driving capacitor and the torque driving capacitor through push-pull and accumulation processing.

[0058] As in this embodiment, Figure 4 As shown in the right half of the diagram, FX1-FX4 and FY1-FY4 are the X-axis and Y-axis force driving electrodes, respectively. The X-axis force driving electrode group FX1, FX2 is differential with the electrode group FX3, FX4, and the Y-axis force driving electrode group FY1, FY2 is differential with the electrode group FY3, FY4. The calculated force balance voltage is applied to the force driving electrode through the push-pull circuit to generate an electrostatic force, so that the mass block works at the reference position. In this embodiment, the voltage applied to FX1 and FX2 is (V FX +V DC1 ), the voltage applied to FX3 and FX4 is (V FX -V DC1 ), the voltage applied to FY1 and FY2 is (V FY +V DC2 ), the voltage applied to FY3 and FY4 is (V FY -V DC2 ), where V FX is the X-axis force balance voltage, V FY is the Y-axis force balance voltage, V DC1 is the X-axis DC bias voltage, V DC2 is the Y-axis DC bias voltage.

[0059] like Figure 5As shown in the right half of the diagram, MX1-MX4 and MY1-MY4 are Z-axis torque drive electrodes. The drive capacitors are divided into two groups of independent drive capacitors: force drive capacitors and torque drive capacitors. Each group of drive capacitors applies a voltage signal independently. The distance drive electrode group MX1, MX3, MY1, MY3 and the electrode group MX2, MX4, MY2, MY4 are differential groups. The calculated distance balance voltage is applied to the distance drive electrode through a push-pull circuit to generate an electrostatic distance, so that the mass block works at the reference angle. In this embodiment, the voltage applied to MX1, MX3, MY1, MY3 is (V FZ +V DC3 ), the voltage applied to MX2, MX4, MY2, and MY4 is (V FZ -V DC3 ), where V FZ is the Z-axis torque balance voltage, V DC3 is the Z-axis DC bias voltage.

[0060] In the control method of the micro-accelerometer, the electrostatic force generated by the force balance voltage on the X-axis and the Y-axis is expressed as follows:

[0061]

[0062]

[0063] Where ε is the dielectric constant, N FX and N FY The number of comb teeth in the force-driven capacitance of the X-axis and Y-axis, S FX and S FY The overlapping area of the comb teeth in the force-driven capacitance of the X-axis and Y-axis, d FX and d FY are the gaps between the teeth of the force-driven capacitors for the X and Y axes, V FX and V FY are the force balance voltages of the X-axis and Y-axis, V DC1 and V DC2 are the DC bias voltages of the X-axis and Y-axis, respectively, and F X and F Y are the electrostatic forces generated along the X and Y axes respectively;

[0064] In the control method of the micro-accelerometer, the electrostatic torque generated by the torque balance voltage on the Z axis is expressed as:

[0065]

[0066] Where ε is the dielectric constant, N FZ is the number of teeth in the torque drive capacitor, L FZ is the distance between the torque-driven comb capacitor and the center of the mass block, hFZ is the thickness of the torque-driven comb teeth, d FZ1 and d FZ2 (d FZ2 >3d FZ1 ) is the gap between the teeth of the torque-driven comb capacitor, V FZ is the torque balance voltage, V DC3 is the Z-axis DC bias voltage, F Z is the electrostatic torque generated on the Z axis.

[0067] Through the above-mentioned drive capacitor arrangement and control method, the force / torque balancing unit generates linear feedback force and torque to maintain the position and rotation angle of the acceleration-sensitive mass block unchanged.

[0068] In the described "zero stiffness" electrostatic tuning method for a closed-loop micromachined accelerometer, the electrostatic tuning voltage is further adjusted in real time based on changes in the force balance and torque balance voltages. The electrostatic tuning voltage, force balance voltage, and torque balance voltage all alter the accelerometer's equivalent stiffness along the X and Y axes. By adjusting the electrostatic tuning voltage, the negative electrostatic stiffness applied along the X and Y axes can be varied, thereby further reducing the equivalent stiffness to a preset value, or even achieving "zero" equivalent stiffness.

[0069] Under the action of the electrostatic trimming voltage, force balance voltage and torque balance voltage, the electrostatic negative stiffness of the X-axis and Y-axis generated by the electrostatic trimming capacitor, force drive capacitor and torque drive capacitor is expressed as follows:

[0070]

[0071]

[0072] Where ε is the dielectric constant, N TX and N TY are the comb teeth logarithms of the electrostatic trimming capacitors on the X and Y axes, S TX and S TY are the overlapping areas of the electrostatic trimming capacitors on the X and Y axes, respectively, and d TX and d TY are the comb gaps in the electrostatic trimming capacitors for the X and Y axes, V TX and V TY are the electrostatic adjustment voltages for the X and Y axes, K X and K Y are the electrostatic negative stiffness generated in the X-axis and Y-axis respectively;

[0073] By establishing an electrostatic adjustment loop, the equivalent stiffness is controlled by calculating the total electrostatic negative stiffness generated by the force balance voltage and the torque balance voltage; the force balance voltage or the torque balance voltage is squared, multiplied by a fixed gain and summed, and the electrostatic adjustment voltage is calculated by comparing it with a preset value and applied to the electrostatic adjustment unit, thereby maintaining the equivalent stiffness of the accelerometer system unchanged.

[0074] Those skilled in the art should understand that the above 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 scope of protection of the present invention.

Claims

1. A three-axis micromachined accelerometer, characterized in that: Including acceleration sensitive element, electrostatic adjustment unit, linear displacement detection unit, angle detection unit, force balance unit, torque balance unit; The acceleration sensitive element includes a single mass block and an elastic beam. The single mass block is composed of multiple distributed mass structures combined by a rigid connecting arm, connected to the movable comb teeth, symmetrically distributed, and connected to the anchor area through an L-shaped elastic beam. The electrostatic adjustment unit includes an electrostatic adjustment electrode and its corresponding electrostatic adjustment comb teeth, and the electrostatic adjustment comb teeth and the first group of fixed comb teeth on the connecting arm form an electrostatic adjustment capacitor; The X-direction electrostatic trimming capacitor generates an electrostatic negative stiffness in the X-axis direction under the action of the X-direction electrostatic trimming voltage, and the Y-direction electrostatic trimming capacitor generates an electrostatic negative stiffness in the Y-axis direction under the action of the Y-direction electrostatic trimming voltage. The electrostatic net force generated by the electrostatic trimming unit in the X-axis and Y-axis directions is zero. The linear displacement detection unit includes a detection electrode and its corresponding detection comb teeth. The detection comb teeth and the third set of fixed comb teeth on the connecting arm form a detection capacitor for realizing X-axis and Y-axis linear displacement detection; The rotation angle detection unit and the linear displacement detection unit share the detection electrodes and detection capacitors, but in different combinations, and are used to realize Z-axis rotation angle detection; The force balancing unit includes a force driving electrode and its corresponding force driving comb teeth, and the force driving comb teeth and the second set of fixed comb teeth on the connecting arm form a force driving capacitor; The torque balancing unit includes a torque driving electrode and its corresponding torque driving comb teeth. The torque driving comb teeth and the fourth group of fixed comb teeth on the connecting arm form a torque driving capacitor.

2. A three-axis micromachined accelerometer according to claim 1, characterized in that: The first group of fixed comb teeth, the second group of fixed comb teeth, the third group of fixed comb teeth and the fourth group of fixed comb teeth are evenly arranged in sequence from the center of the single mass block to the outside along the connecting arm, forming a centrally symmetrical structure.

3. A three-axis micromachined accelerometer according to claim 1, characterized in that: In the linear displacement detection unit, the detection capacitor in the positive direction of the X-axis and the detection capacitor in the negative direction of the X-axis are mutually X-axis detection differential capacitors, and the detection capacitor in the positive direction of the Y-axis and the detection capacitor in the negative direction of the Y-axis are mutually Y-axis detection differential capacitors. By applying a carrier voltage to the detection electrode, carrier modulation of the capacitance change signal caused by the variable gap is realized. The signal on the detection electrode becomes a digital displacement signal after passing through the CV circuit, differential processing, AD conversion circuit, multiplication demodulation and low-pass filtering signal processing.

4. A three-axis micromachined accelerometer according to claim 1, characterized in that: In the described angle detection unit, when the single mass block rotates clockwise around the Z-axis, the detection capacitances with increased and decreased overlapping areas serve as Z-axis detection differential capacitances. By applying a carrier voltage to the detection electrode, carrier modulation of the capacitance change signal caused by the variable area is achieved. The signal on the detection electrode is processed through a CV circuit, differential processing, an AD conversion circuit, multiplication demodulation, and low-pass filtering to become a digital angle signal.

5. The three-axis micromachined accelerometer according to claim 1, characterized in that: In the force balancing unit, the force driving capacitor in the positive direction of the X-axis and the force driving capacitor in the negative direction of the X-axis are mutually X-axis driving differential capacitors, and the force driving capacitor in the positive direction of the Y-axis and the force driving capacitor in the negative direction of the Y-axis are mutually Y-axis driving differential capacitors. The force balancing voltage is calculated based on the displacement signal detected by the linear displacement detection unit, and is applied to the force driving electrode after passing through the push-pull circuit to generate an electrostatic force, so that the single mass block operates in the reference position.

6. A three-axis micromachined accelerometer according to claim 1, characterized in that: In the torque balancing unit, when the single mass block rotates clockwise around the Z-axis, the torque driving capacitor with increased and decreased overlapping area is the Z-axis torque driving differential capacitor. The torque balancing voltage is calculated based on the angle signal detected by the angle detection unit, and is applied to the torque driving electrode after passing through the push-pull circuit to generate an electrostatic torque, so that the single mass block operates at a reference angle.

7. The three-axis micromachined accelerometer according to claim 1, characterized in that: The electrostatic adjustment capacitor, detection capacitor, force-driven capacitor and torque-driven capacitor contain multiple pairs of comb tooth structures, each fixed comb tooth is adjacent to two movable comb teeth, forming two pairs of capacitors with different gaps, and the gap satisfies d2>3d1, where d1 represents the gap between the fixed comb tooth and the first adjacent movable comb tooth, and d2 represents the gap between the fixed comb tooth and the second adjacent movable comb tooth.

8. A control method for a three-axis micromachined accelerometer according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: When the mass block is subjected to external acceleration, carrier modulation is achieved by applying a carrier voltage to the detection electrodes in the linear displacement detection unit and the rotation angle detection unit to generate the capacitance change signal caused by the variable gap and the capacitance change signal caused by the variable area. The signals on the detection electrodes are processed by a CV circuit, differential processing, an AD conversion circuit, multiplication demodulation, and low-pass filtering to obtain digital displacement signals and digital rotation angle signals, respectively. Step 2: The digital displacement signal and the digital rotation angle signal are calculated by the PID controller to obtain the X-axis force balance voltage V FX , Y-axis force balance voltage V FY and Z-axis torque balance voltage V FZ ; Through the push-pull circuit, voltage V is applied to the force driving electrodes corresponding to the X-axis driving differential capacitor. FX +V DC1 and V FX -V DC1 , apply voltage V to the force driving electrodes corresponding to the Y-axis driving differential capacitor FY +V DC2 and V FY -V DC2 , so that the mass block works at the reference position of the XY plane; Among them, V DC1 and V DC2 are the X-axis DC bias voltage and the Y-axis DC bias voltage respectively; Through the push-pull circuit, bias voltage V is applied to the torque driving electrodes corresponding to the Z-axis detection differential capacitance. FZ +V DC3 and V FZ -V DC3 , so that the mass block works at the Z-axis reference angle; where V DC3 is the Z-axis DC bias voltage; Step 3: Use the X-axis force balance voltage, Y-axis force balance voltage, and Z-axis moment balance voltage to calculate the X-axis electrostatic negative stiffness and Y-axis electrostatic negative stiffness generated by the electrostatic force and electrostatic moment, respectively. By comparing them with the equivalent stiffness preset values, the X-axis electrostatic adjustment voltage and Y-axis electrostatic adjustment voltage are calculated and applied to the electrostatic drive electrode through the amplification circuit, thereby keeping the X-axis equivalent stiffness and Y-axis equivalent stiffness constant.

9. The control method of the three-axis micromachined accelerometer according to claim 8, characterized in that: The electrostatic forces generated by the force balance voltage on the X-axis and Y-axis are expressed as: Where ε is the dielectric constant, N FX and N FY The number of comb teeth in the force-driven capacitance of the X-axis and Y-axis, S FX and S FY The overlapping area of the comb teeth in the force-driven capacitance of the X-axis and Y-axis, d FX and d FY The gaps between the teeth of the force-driven capacitors for the X and Y axes, F X and F Y are the electrostatic forces generated along the X and Y axes respectively; The electrostatic torque generated by the torque balancing voltage on the Z axis is expressed as: Where ε is the dielectric constant, N FZ is the number of teeth in the torque drive capacitor, L Fz is the distance between the torque-driven comb capacitor and the center of the mass block, h FZ is the thickness of the torque-driven comb teeth, d Fz1 and d FZ2 is the gap between the teeth of the torque-driven comb capacitor, F Z is the electrostatic torque generated on the Z axis.

10. The control method of the three-axis micromachined accelerometer according to claim 8, characterized in that: The X-axis total electrostatic negative stiffness and the Y-axis total electrostatic negative stiffness generated by the X-axis force balance voltage, the X-axis electrostatic adjustment voltage, the X-axis DC bias voltage, the Y-axis force balance voltage, the Y-axis electrostatic adjustment voltage, the Y-axis DC bias voltage, the Z-axis moment balance voltage, and the Z-axis DC bias voltage are respectively expressed as: Where ε is the dielectric constant, N TX and N TY are the comb teeth logarithms of the electrostatic trimming capacitors on the X and Y axes, S TX and S TY are the overlapping areas of the electrostatic trimming capacitors on the X and Y axes, respectively, and d TX and d TY are the comb gaps in the electrostatic trimming capacitors for the X and Y axes, respectively, and K X and K Y are the electrostatic negative stiffness generated in the X-axis and Y-axis respectively.

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