CN117288981A - Z-axis micromechanical accelerometer and control method thereof - Google Patents
Z-axis micromechanical accelerometer and control method thereof Download PDFInfo
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- CN117288981A CN117288981A CN202311241098.5A CN202311241098A CN117288981A CN 117288981 A CN117288981 A CN 117288981A CN 202311241098 A CN202311241098 A CN 202311241098A CN 117288981 A CN117288981 A CN 117288981A
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- 238000009966 trimming Methods 0.000 claims description 16
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/125—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by capacitive pick-up
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Abstract
The invention discloses a Z-axis micromechanical accelerometer and a control method thereof, and belongs to the technical field of acceleration measurement. An asymmetric seesaw sensitive structure is formed by adopting a mass block and a torsion elastic beam, and two symmetrical multifunctional capacitors are formed by designing electrodes below the two mass blocks. Torsion of the teeterboard structure under the action of Z-axis acceleration can be detected through the change of differential capacitance of the capacitor, and at the moment, the capacitor is used for detection; according to the change of the detected torsion angle and the PID controller, PWM voltage for realizing force balance control can be calculated and applied to symmetrical capacitors together with DC tuning voltage in a push-pull mode, so that constant static negative stiffness can be generated, equivalent stiffness of the seesaw sensitive element can be reduced, static resultant force which can be modulated through PWM can be generated, the position of the seesaw sensitive structure can be kept constant, closed loop detection is realized, and the PWM voltage can reflect the magnitude of external acceleration.
Description
Technical Field
The invention belongs to the technical field of acceleration measurement, and particularly relates to a micromechanical accelerometer and a control method thereof.
Background
Most of Z-axis micro accelerometers adopt a sandwich structure, detection/driving electrodes are required to be designed above and below a mass block to form a three-layer structure, the problems of complex processing technology and low electrode integration level exist, and in order to ensure processing reliability, the rigidity of a Z-axis elastic beam is usually quite high, so that the improvement of detection precision is limited. The micro-accelerometer with the teeterboard structure is simpler in structure, has a two-layer structure, reduces the processing technology, but also has the problem that the detection/driving electrode is required to be independently designed and the torsional rigidity is increased, and limits the integration and the precision of the micro-accelerometer.
Disclosure of Invention
Aiming at the defects and shortcomings of the existing Z-axis micromechanical accelerometer, the invention provides the Z-axis micromechanical accelerometer and a control method thereof, Z-axis rotation sensing is realized by utilizing asymmetrically arranged mass blocks and torsion elastic beams, electrostatic trimming, corner detection and force balance are realized simultaneously by utilizing a multifunctional multiplexing capacitor formed between a multifunctional multiplexing electrode and the mass blocks, the closed-loop acceleration detection of the Z-axis is realized by adopting a closed-loop control method, the equivalent rigidity of the accelerometer can be regulated to zero by utilizing the electrostatic trimming method in the control method, so that the detection precision of the accelerometer is improved, the interference of signals of each path is avoided, and the accelerometer and the control method thereof are simpler and more practical.
The technical scheme adopted by the invention is as follows:
in a first aspect, the invention provides a Z-axis micromechanical accelerometer, comprising a teeter-totter structure and a multifunctional multiplexing electrode;
the teeterboard structure comprises a torsional elastic beam and mass blocks which are asymmetrically distributed on two sides of the torsional elastic beam, wherein the mass blocks are of a rigid structure and are fixedly supported on an anchor area structure together with torsional elasticity Liang Gulian, a mass block plane is defined as an X-Y plane, and the asymmetric mass blocks refer to that the gravity center of the rigid mass block is not coincident with a torsional central axis in the Y direction, namely, the gravity center of the rigid mass block is a certain distance from the torsional central axis in the XY horizontal direction, namely, the gravity center of the mass block is a certain distance from the torsional central axis of the torsional elastic beam;
the multifunctional multiplexing electrode is fixed on the substrate on one side of the mass block in the Z direction and comprises a first electrode and a second electrode which are equal in distance from a torsion central shaft.
The teeterboard structure and the multifunctional multiplexing electrode form a sensitive element, and can be equivalently a second-order mass-spring system, and the equivalent stiffness of the teeterboard structure comprises the stiffness of a torsional elastic beam and the static negative stiffness;
further, the multifunctional multiplexing electrode and the mass block in the teeterboard structure form a group of differential capacitors, and the group of differential capacitors can multiplex the corner detection capacitor, the rigidity tuning capacitor and the force balance capacitor, so that the mutual interference of signals can be avoided through electrostatic trimming and force balance control voltage based on PWM.
Further, the corner detection capacitor is used for detecting the torsion angle change of the teeterboard structure by respectively applying high-frequency carrier voltage V to the electrodes of the differential capacitor c and-V c The carrier modulation of the capacitance change signal caused by the change gap is realized, and the signal on the mass block is processed by a CV circuit, an AD conversion circuit, a multiplication demodulation circuit and a low-pass filtering signal to become a digital corner signal.
Further, the stiffness tuning capacitor is used for generating static negative stiffness by applying push-pull control voltage V to electrodes of the differential capacitor 1 +V 2 +V c And V 1 －V 2 －V c Generating electrostatic negative stiffness, wherein V 1 For electrostatic trimming voltage, V 2 To force balance the PWM voltage, the electrostatic negative stiffness value and V 1 2 +V 2 2 Proportional relation by adjusting V 1 Or V 2 The magnitude can vary the equivalent stiffness magnitude.
Further, the force balance capacitor is used for generating electrostatic moment to counteract inertial force generated by external acceleration, and push-pull control voltage V is applied to the electrodes of the differential capacitor 1 +V 2 And V 1 －V 2 Generating electrostatic torque, electrostatic torque and V 1 ·V 2 In proportional relation by adjusting amplitude to V 2 The duty cycle of the PWM voltage of (c) may vary the magnitude of the electrostatic torque.
In a second aspect, the present invention provides a control method of the Z-axis micromechanical accelerometer, where the position of the mass is stabilized on a reference angle in a force balance manner, and the equivalent stiffness is reduced to a preset value by applying electrostatic negative stiffness, including the following steps:
step 1, calculating and adjusting according to a calibrated torsional elastic beam rigidity value and a preset equivalent rigidity valueHarmonic static negative rigidity, and calculates static trimming voltage V according to the following formula 1 ：
Wherein epsilon is dielectric constant, S is capacitance overlap area, d 0 For capacitance gap, k m And k eff Respectively a calibrated torsional elastic beam stiffness value and a preset equivalent stiffness value, |V 2 And I is the magnitude of the force balance PWM voltage.
Step 2, when the mass is subjected to external acceleration, a pair of carrier voltages V with the same amplitude and opposite signs are applied to the first electrode 2 and the second electrode 5 c I.e. applying high-frequency carrier voltages V to the two sets of electrodes respectively c and-V c At the moment, two groups of capacitors are used as corner detection capacitors to realize carrier modulation of capacitance change signals caused by a variable gap, and digital corner signals are respectively obtained after signals of a mass block are processed by a CV circuit, an AD conversion circuit, multiplication demodulation and low-pass filtering signals;
step 3, calculating the digital rotation angle signal through a PID controller to obtain a Z-axis force balance PWM voltage V 2 A duty cycle; the voltage V is continuously applied to the first electrode 2 and the second electrode 5 respectively through the push-pull circuit 1 +V 2 And V 1 －V 2 At the moment, the two groups of capacitors are used as Z-axis driving capacitors, so that the mass block is maintained at a constant horizontal reference position, and the equivalent rigidity can be adjusted to a preset value; wherein V is 1 And V 2 The Z-axis electrostatic trimming voltage and the Z-axis force balancing PWM voltage are respectively adopted;
the detected acceleration can be expressed as:
wherein ε is the dielectric constant, m is the mass of the mass, S and d 0 Capacitance overlap area and gap, L 1 And L 2 Respectively in the middle of winding and twistingMoment arm corresponding to moment of inertia generated by asymmetric mass of mandrel and moment arm corresponding to electrostatic moment generated by force balance capacitor, V 1 And |V 2 And the I is the electrostatic trimming voltage and the force balance PWM voltage amplitude, and b is the force balance PWM voltage duty ratio.
In general, compared with the prior art, the technical scheme conceived by the invention has the following beneficial effects:
(1) The Z-axis micro-mechanical acceleration detection device realizes Z-axis acceleration closed loop detection by designing the Z-axis micro-mechanical acceleration with a double-layer structure, comprising the asymmetric mass block, the torsion elastic beam and the multifunctional multiplexing capacitor, and has the advantages of simple processing technology, high integration level, miniaturization and the like.
(2) According to the invention, the rotation angle detection, the static adjustment and the force balance are realized through multiplexing the capacitor, and the static adjustment and the force balance control method based on PWM is provided, so that the electrode integrated design is realized, and the mutual interference of signals is avoided.
(3) The invention simultaneously applies the force balance closed-loop control and the static trimming technology, can improve the linearity and the precision of the micromechanical accelerometer, and the proposed force balance and equivalent stiffness control method is easy to realize in a digital controller.
(4) The micro-mechanical accelerometer can be independent of a high-difficulty silicon processing technology, and can simply realize preset low equivalent stiffness and even quasi-zero equivalent stiffness by using an electrostatic trimming technology.
Drawings
FIG. 1 is a schematic structural diagram of a Z-axis micromechanical accelerometer according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a control method of a Z-axis micromechanical accelerometer according to an embodiment of the present invention;
the same reference numerals are used to denote the same structures throughout the figures, wherein: 1-asymmetric mass, 2-first electrode, 3-torsion elastic beam, 4-anchor region, 5-second electrode, V 1 Electrostatic trimming voltage, V 2 Force balanced PWM voltage, V c Carrier voltage, C/V-capacitor/voltage converter, AD-A/D converter, LPF-low pass filterPID-proportional-integral-derivative controller.
Detailed Description
For a clearer description of the objects, technical solutions and advantages of the present invention, reference is made to the following drawings and the formula derivatives. It should be understood that the principles herein are for purposes of illustration and not limitation.
The invention comprises an asymmetric mass block, a torsion elastic beam, an electrode, an anchor area and other structures. Fig. 1 is a schematic structural diagram of a Z-axis micromechanical accelerometer according to an embodiment of the present invention, including a mass 1, a first electrode 2, a torsionally elastic beam 3, an anchor region 4, and a second electrode 5. The first electrode 2 and the second electrode 5 and the mass block respectively form a group of capacitors, and can be multiplexed into a corner detection capacitor, an electrostatic trimming capacitor and a force balance capacitor.
The torsional elastic beam and the mass blocks asymmetrically distributed on two sides of the torsional elastic beam form a teeterboard structure, wherein the mass blocks are of a rigid structure and are connected with torsional elasticity Liang Gulian, two ends of the torsional elastic beam are fixedly supported on the anchor area structure, and a distance exists between the gravity center of the mass blocks and the torsional central shaft of the torsional elastic beam. The first electrode 2 and the second electrode 5 are fixed on the substrate on one side of the mass block in the Z direction. In this embodiment, the mass blocks are symmetrical about an axis perpendicular to the torsion central axis in the X-Y plane, that is, the symmetry axis is the Y direction, where the asymmetric mass blocks refer to mass blocks that are asymmetrically disposed with respect to the torsion elastic beam in the X direction, and the lengths of the mass blocks distributed on two sides of the torsion elastic beam along the X direction are different, and the widths along the Y direction and the thicknesses along the Z direction are the same. As shown in the cross-sectional view of the teeterboard structure of fig. 2, in order to secure the elasticity of the torsion elastic beam, the thickness of the elastic beam is smaller than the thickness of the mass.
The Z-axis micro-mechanical accelerometer designed by the invention has a simple structure, integrates detection, tuning and driving functions, avoids mutual interference, and is beneficial to improving the miniaturization, integration level and precision of the Z-axis accelerometer.
When the external acceleration of the Z axis exists, the gravity center of the asymmetric mass block is not coincident with the torsion shaft, so that the inertia force can generate torque to rotate around the shaftBecause the capacitors are symmetrically distributed on two sides of the torsion central shaft, the gaps of one group of capacitors become larger, the gaps of the other group of capacitors become smaller, when the rotation angle is extremely small (the force balance is established), the capacitors can be assumed to be parallel plate capacitors at the moment, and the two groups of capacitors are differentiated and then pass through a C/V conversion circuit and an AD conversion circuit, and voltage signals representing the rotation angle can be output through demodulation and low-pass filtering operation; the voltage signal is calculated by a PID controller to obtain a force balance PWM control voltage V 2 . The voltages respectively applied to the two groups of capacitor electrodes through the push-pull circuit are respectively V 1 +V 2 +V c And V 1 －V 2 －V c Wherein V is 1 In addition, because the carrier voltage is a high-frequency signal, the DC tuning voltage can be omitted in the calculation of electrostatic force and electrostatic negative stiffness, and V 2 For PWM control voltage, only the duty cycle changes during force balancing, thus V 1 2 +V 2 2 The static negative rigidity is kept unchanged, so that the static negative rigidity is kept unchanged, and the mutual interference of force balance and static trimming is avoided.
Based on the electrostatic trimming capacitor, the equivalent stiffness of the system can be adjusted, and the corresponding direct current tuning voltage V 1 Can be expressed as:
wherein epsilon is dielectric constant, S is capacitance overlap area, d 0 For capacitance gap, k m And k eff Respectively a calibrated torsional elastic beam stiffness value and a preset equivalent stiffness value, |V 2 And I is the magnitude of the force balance PWM voltage.
Based on the force balance capacitance, Z-axis acceleration detection can be achieved, and the acceleration can be expressed as:
wherein ε is the dielectric constant, m is the mass, S and d 0 Respectively, capacitor acArea of stack and gap, L 1 L is the moment arm corresponding to the moment of inertia about the torsional center axis generated by asymmetrically distributed masses 2 For the arm of force, V, corresponding to the electrostatic moment about the torsion central axis generated by the force balance capacitor 1 And |V 2 I is the dc tuning voltage and the force-balanced PWM voltage amplitude, respectively, and b is the force-balanced PWM voltage duty cycle.
It should be understood by those skilled in the art that the foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the invention, but any modifications, equivalents, improvements and modifications within the spirit and principles of the invention are intended to be included within the scope of the present invention.
Claims (8)
1. The Z-axis micromechanical accelerometer is characterized by comprising a teeterboard structure and a multifunctional multiplexing electrode;
the teeterboard structure comprises a torsional elastic beam and mass blocks which are asymmetrically distributed on two sides of the torsional elastic beam, wherein the mass blocks are of a rigid structure and are together with torsional elasticity Liang Gulian, two ends of the torsional elastic beam are fixedly supported on the anchor area structure, and a distance exists between the gravity center of the mass blocks and the torsional central shaft of the torsional elastic beam;
the multifunctional multiplexing electrode is fixed on the substrate on one side of the mass block in the Z direction and comprises a first electrode and a second electrode which are equal in distance from a torsion central shaft.
2. The Z-axis micromechanical accelerometer of claim 1, wherein the masses are symmetrical about an axis in the X-Y plane that is perpendicular to the torsion central axis.
3. The Z-axis micro-mechanical accelerometer of claim 1, wherein the multi-functional multiplexing electrode and the mass in the teeter-totter structure form a set of differential capacitors that are capable of multiplexing the corner detection capacitance, the stiffness tuning capacitance, and the force balance capacitance.
4. According to claimThe Z-axis micro-mechanical accelerometer of claim 3, wherein said rotation angle detection capacitor is used for detecting the torsion angle change of the teeterboard structure by respectively applying high-frequency carrier voltage V to the electrodes of the differential capacitor c and-V c The carrier modulation of the capacitance change signal caused by the change of the gap is realized, and the digital rotation angle signal is obtained.
5. A Z-axis micromechanical accelerometer according to claim 3, characterized in that the stiffness tuning capacitor is adapted to generate an electrostatic negative stiffness by applying a push-pull control voltage V to the electrodes of the differential capacitor 1 +V 2 +V c And V 1 －V 2 －V c Generating electrostatic negative stiffness, wherein V 1 For electrostatic trimming voltage, V 2 To force balance the PWM voltage, the electrostatic negative stiffness value and V 1 2 +V 2 2 Proportional relationship.
6. A Z-axis micromechanical accelerometer according to claim 3, characterized in that the force balance capacitor is adapted to generate an electrostatic moment to counteract an inertial force generated by an external acceleration by applying a push-pull control voltage V to the electrodes of the differential capacitor 1 +V 2 And V 1 －V 2 Generating electrostatic torque, electrostatic torque and V 1 ·V 2 Proportional relationship.
7. A control method based on the Z-axis micromechanical accelerometer according to claim 3, characterized in that it comprises the following steps:
step 1, calculating tuning electrostatic negative stiffness according to a calibrated torsional elastic beam stiffness value and a preset equivalent stiffness value, and calculating electrostatic trimming voltage V according to the following formula 1 ：
Wherein epsilon is dielectric constant, S is capacitance overlap area，d 0 For capacitance gap, k m And k eff Respectively a calibrated torsional elastic beam stiffness value and a preset equivalent stiffness value, |V 2 I is the magnitude of the force balance PWM voltage;
step 2, when the mass block receives external acceleration, a pair of carrier voltages with the same amplitude and opposite signs are applied to the multifunctional multiplexing electrode to realize carrier modulation of capacitance change signals caused by variable gaps, and digital rotation angle signals are respectively obtained after signals of the mass block are processed by a CV circuit, an AD conversion circuit, multiplication demodulation and low-pass filtering signals;
step 3, calculating the digital rotation angle signal through a PID controller to obtain a Z-axis force balance PWM voltage V 2 A duty cycle;
the voltage V is continuously applied to the multifunctional multiplexing electrodes through the push-pull circuit 1 +V 2 And V 1 －V 2 The method comprises the steps of enabling a mass block to be maintained at a constant horizontal reference position, calculating acceleration, and adjusting equivalent rigidity to a preset value; wherein V is 1 And V 2 The electrostatic trimming voltage and the force balancing PWM voltage are respectively.
8. The method for controlling a Z-axis micro-mechanical accelerometer according to claim 7, wherein the acceleration calculation formula is:
wherein m is the mass of the mass block, L 1 L is the moment arm corresponding to the moment of inertia about the torsional center axis generated by asymmetrically distributed masses 2 And b is the duty ratio of the force balance PWM voltage, which is the arm of force corresponding to the electrostatic moment generated by the force balance capacitor around the torsion central axis.
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