1. A micromechanical accelerometer is characterized by comprising an acceleration sensitive unit, an electrostatic rigidity unit, a displacement detection unit and a force balance unit;

the acceleration sensing unit comprises a mass block and an elastic beam structure, and the mass block is connected with an anchor area in the direction of the horizontal sensing shaft through the elastic beam structure;

the static rigidity unit is composed of bilateral parallel plate type comb capacitors (4) and comprises moving comb teeth and fixed comb teeth, the moving comb teeth are connected with the mass block, the fixed comb teeth are connected with the anchor area, the moving comb teeth and the fixed comb teeth are symmetrically distributed in a central axis manner, namely, the moving comb teeth are consistent with gaps of the fixed comb teeth along the positive and negative directions of a horizontal sensitive axis; the bilateral parallel plate type comb capacitors (4) generate electrostatic negative stiffness under the action of bias tuning voltage;

the displacement detection unit consists of a group of displacement detection differential variable-area capacitors (5) and corresponding differential electrodes, and carrier modulation of capacitance change signals is realized by applying carrier voltages with the same amplitude and opposite signs on the differential electrodes;

the force balance unit consists of a group of force balance differential variable area capacitors (3) and corresponding differential electrodes, and the mass block works on a reference position by applying force balance voltage on the differential electrodes.

2. A method of calibration compensation of a micro-mechanical accelerometer according to claim 1, comprising a closed-loop reference position calibration compensation method and an equivalent stiffness calibration compensation method;

the closed-loop reference position calibration compensation method comprises the following steps:

1.1) selecting an initial position as a force balance feedback reference position, completing closed-loop control of the accelerometer, and applying a tuning voltage V on the electrostatic stiffness unit_t；

1.2) introducing a frequency omega to the bias tuning voltage_oThe out-of-bandwidth calibration signal of (a);

1.3) the mass block can generate displacement change when being subjected to acceleration in the direction of the horizontal sensitive shaft, so that a capacitance change signal can be generated between the mass block and a displacement detection differential variable-area capacitor; sequentially carrying out carrier demodulation and frequency omega calibration on the capacitance change signal_oDemodulating and low-pass filtering to obtain displacement disturbance V_s0；

1.4) perturbing the quantity V_s0Obtaining a reference position compensation control quantity delta V through proportional, integral and differential operation_yrefAdded to the initial reference position signal V_yrefOn, the reference position signal V 'is updated'_yref＝V_yref+ΔV_yrefUntil the displacement disturbance quantity is reduced to zero, the bilateral parallel plate type comb capacitor is at a symmetrical zero position;

the equivalent stiffness calibration compensation method comprises the following steps:

2.1) applying a fixed force balance voltage on a differential electrode of the force balance differential variable area capacitor under open loop control, so that the accelerometer works on the reference position after calibration in the step 1.4); the force balance voltage is generated by a force balance control signal through a push-pull circuit;

2.2) obtaining the critical pull-in voltage V by gradually increasing the tuning voltage until the pull-in phenomenon of the accelerometer under the open-loop control_pi；

2.3) Re-closed loop control of the reference position signal V 'in closed loop'_yrefAdding a frequency of omega_iAnd sets the tuning voltage to V_t＝αV_piAnd alpha is a voltage coefficient;

2.4) calibrating the frequency omega of the force balance control signal fed back in a closed loop_iDemodulating and low-pass filtering to obtain a voltage signal V representing equivalent stiffness_kref。

2.5) converting the voltage signal V_krefSetting as a reference stiffness value, establishing a stiffness compensation closed loop, specifically, extracting an updated voltage signal V 'representing equivalent stiffness according to the method of step 2.4)'_krefWill V_krefAnd V'_krefThe deviation value is subjected to proportional, integral and differential operation to obtain the compensation quantity delta V of the tuning voltage_tIs added to the initial tuning voltage V_tThereby maintaining the equivalent stiffness value at the reference stiffness value at all times.

3. The method of claim 2, wherein the out-of-band calibration signal and the in-band calibration signal are sinusoidal signals or square wave signals.

4. The method for calibrating and compensating a micro-mechanical accelerometer according to claim 2, wherein the expression of the equivalent electrostatic negative stiffness of the bilateral parallel plate comb capacitors is as follows:

V_t＝αV_pi

wherein k is_eleEquivalent electrostatic negative stiffness of bilateral parallel plate type comb tooth capacitor, epsilon is dielectric constant, A is overlapping area of fixed comb tooth and movable comb tooth, and V is_tFor tuning the voltage, V_piIs a pull-in voltage, alpha is a voltage coefficient, d₀Is an initial gap of a moving comb tooth and a fixed comb tooth in a bilateral parallel plate type comb tooth capacitor, y_refFor reference displacement, k is the mechanical stiffness of the accelerometer.

Background

Through the electrostatic trimming technology, the equivalent rigidity of the micro-mechanical accelerometer can be reduced, the range and the sensitivity of the micro-mechanical accelerometer are changed, and meanwhile, in order to improve the range and the linearity of the micro-mechanical accelerometer, the micro-mechanical accelerometer can work in an electrostatic trimming and closed-loop control state at the same time. The asymmetric comb capacitor is an electrostatic trimming design commonly used in the field of MEMS, and can be used for reducing the equivalent stiffness of a micromechanical accelerometer or gyroscope to realize stiffness trimming; and the pull-in voltage and pull-in time of the asymmetric comb capacitor can also be used for acceleration measurement. However, the adoption of the asymmetric comb capacitors can change the central position of the accelerometer and introduce the problem of asymmetry. On the other hand, the micro mechanical accelerometer is influenced by temperature to generate a drift effect, and is one of the key problems restricting the measurement accuracy of the acceleration. Currently, most methods for actively suppressing the output drift of the micro-mechanical accelerometer rely on a temperature sensor, but at the same time, the complexity of the micro-mechanical accelerometer system is increased.

Disclosure of Invention

Aiming at the defects and shortcomings of the existing micro mechanical accelerometer, the invention provides the micro mechanical accelerometer and the calibration compensation method thereof.

The technical scheme adopted by the invention is as follows:

a micro-mechanical accelerometer comprises an acceleration sensitive unit, an electrostatic rigidity unit, a displacement detection unit and a force balance unit;

the acceleration sensing unit comprises a mass block and an elastic beam structure, and the mass block is connected with an anchor area in the direction of the horizontal sensing shaft through the elastic beam structure;

the static rigidity unit is composed of bilateral parallel plate type comb capacitors and comprises moving comb teeth and fixed comb teeth, the moving comb teeth are connected with the mass block, the fixed comb teeth are connected with the anchor area, the moving comb teeth and the fixed comb teeth are symmetrically distributed in a central axis manner, namely, the moving comb teeth are consistent with gaps of the fixed comb teeth along the positive and negative directions of a horizontal sensitive axis; the bilateral parallel plate type comb capacitor generates electrostatic negative stiffness under the action of bias tuning voltage;

the displacement detection unit consists of a group of displacement detection differential variable-area capacitors and corresponding differential electrodes, and carrier modulation of capacitance change signals is realized by applying carrier voltages with the same amplitude and opposite signs on the differential electrodes;

the force balance unit consists of a group of force balance differential variable area capacitors and corresponding differential electrodes, and the mass block works on a reference position by applying force balance voltage on the differential electrodes.

A calibration control method of the micro-mechanical accelerometer comprises a closed-loop reference position calibration compensation method and an equivalent stiffness calibration compensation method;

the closed-loop reference position calibration compensation method comprises the following steps:

1.1) selecting an initial position as a force balance feedback reference position, completing closed-loop control of the accelerometer, and applying a tuning voltage V on the electrostatic stiffness unit_t；

1.2) introducing a frequency omega to the bias tuning voltage_oThe out-of-bandwidth calibration signal of (a);

1.3) the mass block can generate displacement change when being subjected to acceleration in the direction of the horizontal sensitive shaft, so that a capacitance change signal can be generated between the mass block and a displacement detection differential variable-area capacitor; sequentially carrying out carrier demodulation and frequency omega calibration on the capacitance change signal_oDemodulating and low-pass filtering to obtain displacement disturbance V_s0；

1.4) perturbing the quantity V_s0Obtaining a reference position compensation control quantity delta V through proportional, integral and differential operation_yrefAdded to the initial reference position signal V_yrefOn, the reference position signal V 'is updated'_yref＝V_yref+ΔV_yrefUntil the displacement disturbance amount is reduced to zero, at which time, the twoThe side parallel plate type comb tooth capacitor is at a symmetrical zero position;

the equivalent stiffness calibration compensation method comprises the following steps:

2.1) applying a fixed force balance voltage on a differential electrode of the force balance differential variable area capacitor under open loop control, so that the accelerometer works on the reference position after calibration in the step 1.4); the force balance voltage is generated by a force balance control signal through a push-pull circuit;

2.2) obtaining the critical pull-in voltage V by gradually increasing the tuning voltage until the pull-in phenomenon of the accelerometer under the open-loop control_pi；

2.3) Re-closed loop control of the reference position signal V 'in closed loop'_yrefAdding a frequency of omega_iAnd sets the tuning voltage to V_t＝αV_piAnd alpha is a voltage coefficient;

2.4) calibrating the frequency omega of the force balance control signal fed back in a closed loop_iDemodulating and low-pass filtering to obtain a voltage signal V representing equivalent stiffness_kref。

2.5) converting the voltage signal V_krefSetting as a reference stiffness value, establishing a stiffness compensation closed loop, specifically, extracting an updated voltage signal V 'representing equivalent stiffness according to the method of step 2.4)'_krefWill V_krefAnd V'_krefThe deviation value is subjected to proportional, integral and differential operation to obtain the compensation quantity delta V of the tuning voltage_tIs added to the initial tuning voltage V_tThereby maintaining the equivalent stiffness value at the reference stiffness value at all times.

Preferably, the out-of-bandwidth calibration signal and the in-bandwidth calibration signal are sinusoidal signals or square wave signals.

Preferably, the expression of the equivalent electrostatic negative stiffness of the bilateral parallel plate type comb capacitor is as follows:

V_t＝αV_pi

wherein k is_eleEquivalent electrostatic negative stiffness of bilateral parallel plate type comb tooth capacitor, epsilon is dielectric constant, A is overlapping area of fixed comb tooth and movable comb tooth, and V is_tFor tuning the voltage, V_piIs a pull-in voltage, alpha is a voltage coefficient, d₀Is an initial gap of a moving comb tooth and a fixed comb tooth in a bilateral parallel plate type comb tooth capacitor, y_refFor reference displacement, k is the mechanical stiffness of the accelerometer.

Generally, compared with the prior art, the technical scheme of the invention has the following beneficial effects:

(1) the invention simultaneously applies the static electricity adjustment and the force balance closed-loop control technology, can improve the range, the linearity and the precision of the micro mechanical accelerometer, and broadens the application scene and the working mode of the micro mechanical accelerometer.

(2) According to the method, the reference position and the equivalent stiffness are decoupled, the automatic calibration and the compensation closed-loop control of the reference position and the equivalent stiffness are respectively realized, and the output drift of the micro-mechanical accelerometer can be actively inhibited.

(3) The micromechanical accelerometer can simply realize low rigidity and even quasi-zero rigidity by utilizing an electrostatic trimming technology under the condition of low requirements on a processing technology, and the rigidity calibration control method provided by the invention is easy to realize in a digital controller.

Drawings

Fig. 1 is a schematic structural diagram of a micro-mechanical accelerometer according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of control signals for a micro-machined accelerometer according to an embodiment of the invention;

FIG. 3 is a schematic diagram of a closed-loop reference position calibration and compensation control process for a micro-mechanical accelerometer according to the present invention;

FIG. 4 is a schematic diagram of an equivalent stiffness calibration and compensation control process of the micro-mechanical accelerometer of the present invention;

the same reference numbers will be used throughout the drawings to refer to the same structure, wherein: 1 is an anchor area, 2 is an elastic beam structure, 3 is a force balance differential variable area capacitor, 4 is a bilateral parallel plate type comb capacitor, 5 is a displacement detection differential variable area capacitor, V_aFor force-balanced closed-loop control of voltage, V_bFor balancing the circuit bias voltage, V_cIs a carrier voltage, V_sIs a displacement equivalent voltage, V_tIs the tuning voltage.

Detailed Description

In order to more clearly express the objects, technical solutions and advantages of the present invention, the following derivation is further explained with reference to the drawings and formulas. It is to be understood that the principles herein are to be interpreted as illustrative, and not in a limiting sense.

The invention comprises a mass block, an elastic beam, a bilateral parallel plate type comb capacitor, a variable area capacitor and other structures. Fig. 1 is a schematic structural diagram of a micro-mechanical accelerometer according to an embodiment of the present invention, which includes an anchor area 1, an elastic beam structure 2, a force balance differential variable area capacitor 3, a bilateral parallel plate comb capacitor 4, and a displacement detection differential variable area capacitor 5.

With reference to fig. 1 and 2, the acceleration sensing unit includes a mass and a flexible beam structure, and the mass is connected to the anchor region in the horizontal sensing axis direction through the flexible beam structure.

The static rigidity unit is composed of a bilateral parallel plate type comb tooth capacitor 4 and comprises a movable comb tooth and a fixed comb tooth, the movable comb tooth is connected with the mass block, the fixed comb tooth is connected with the anchor area, the movable comb tooth and the fixed comb tooth are symmetrically distributed in a central axis manner, namely, the gap between the movable comb tooth and the fixed comb tooth is consistent along the positive and negative directions of the sensitive axis; the bilateral parallel plate type comb capacitor 4 is at the bias tuning voltage V_tUnder the action of the static electricity, the negative rigidity is generated.

The displacement detection unit is composed of a group of displacement detection differential variable-area capacitors 5, and carrier voltages +/-V with the same amplitude and opposite signs are applied to differential electrodes_cAnd is combined withCapacitance change signals are led out of the mass block electrodes, and displacement equivalent voltage V representing displacement signals is obtained through CV readout circuits and carrier demodulation_s。

The force balance unit is composed of a group of force balance differential variable area capacitors 3, a pair of force balance voltages V applied to the differential electrodes are obtained by a force balance control signal through a push-pull circuit_b±V_a. The mass operates at a reference position by applying a balancing voltage across the differential electrodes.

The electrostatic stiffness unit can generate equivalent negative stiffness under a certain tuning voltage, and the expression is as follows:

wherein the tuning voltage V_t＝αV_pi(alpha is a voltage coefficient) and critical pull-in voltagek is the mechanical stiffness of the accelerometer, d₀The initial gap between the moving comb teeth and the fixed comb teeth in the bilateral parallel plate type comb tooth capacitor is epsilon, epsilon is dielectric constant, A is overlapping area, y_refFor reference displacement, k_eleThe equivalent negative stiffness of the bilateral parallel plate type comb capacitor is provided.

Therefore, the equivalent stiffness of the accelerometer can be adjusted by changing the tuning voltage, and when the reference position of the comb capacitor is at a zero point, the equivalent electrostatic stiffness and the tuning voltage form a square relation.

The micromechanical accelerometer can work in an open-loop detection mode and a closed-loop detection mode, wherein in the closed-loop detection mode, the force balance unit generates an electrostatic force capable of completely offsetting the inertia force of the mass block. When the actual position of the comb capacitor is not at the zero point, the force balance unit needs to additionally compensate the electrostatic force and the elastic force of the comb, and at the moment, the electrostatic force F of the comb capacitor_tSum-force balanced differential area-variable capacitive electrostatic force F_aThe expression of (a) is:

F_a＝(α²-1)ky

wherein the tuning voltage V_t＝αV_piPull-in voltagey is the actual displacement.

From the above formula, the electrostatic force generated by the force balance unit is determined by α, k and y. When y is fixed, the force balance unit controls the voltage and the equivalent stiffness (alpha)²-1) k is proportional. Therefore, a voltage signal representing equivalent stiffness can be extracted by introducing a calibration signal into a reference position in a bandwidth range and demodulating a response signal from a force balance control signal fed back by the closed loop, and a stiffness compensation closed loop can be established by changing tuning voltage.

When the reference position of the comb capacitor deviates from the zero point, i.e. y is not equal to 0, the electrostatic force of the comb capacitor is not zero and is in direct proportion to the displacement. Therefore, the calibration of the closed-loop reference position can be completed by introducing an out-of-bandwidth calibration signal to the tuning voltage and demodulating a response signal at the displacement equivalent voltage, and the closed-loop compensation reference position is further established and returned to the zero point.

Based on the above characteristics of the micro-mechanical accelerometer, in one specific implementation of the invention, the reference position in the force balance closed loop is calibrated and compensated and controlled, so that the comb capacitance of the accelerometer is always in the zero position.

Based on the above characteristics of the micro-mechanical accelerometer, in one specific implementation of the present invention, the equivalent stiffness of the accelerometer is calibrated and compensated, so as to maintain the equivalent stiffness of the accelerometer constant during the operation process, and the interference caused by the equivalent stiffness to the acceleration measurement can be eliminated by a related detection method and the like.

The accelerometer reference position calibration and compensation method and the equivalent stiffness calibration and compensation method proposed by the present invention are specifically described below with reference to the schematic diagrams shown in fig. 3 and 4.

FIG. 3 is a closed-loop reference position calibration and compensation method:

1) firstly, selecting an initial position as a force balance feedback reference position, completing closed-loop control of the accelerometer, and applying a tuning voltage V on the electrostatic stiffness unit_t。

2) By biasing the tuning voltage V_tIntroducing an out-of-band calibration signal, which can be a sinusoidal signal or a square wave signal (with frequency of omega)_o) When the mass block is subjected to acceleration in the horizontal sensitive direction, displacement change occurs, and accordingly a capacitance change signal is generated.

3) Carrying out carrier modulation and twice demodulation on the capacitance change signal, wherein the first time is carrier demodulation (the demodulation frequency is omega)_c) Second time of calibration frequency demodulation (demodulation frequency is omega)_o) Obtaining a displacement disturbance V through low-pass filtering_s0。

4) Disturbance V in the controller_s0Obtaining a reference position correction control quantity delta V through proportional, integral and differential operation_yrefSuperimposed on the initial reference position control signal V_yrefTo is V'_yref＝V_yref+ΔV_yref。

5) The 2-4 steps are automatic online updating processes.

FIG. 4 is an equivalent stiffness calibration and compensation method:

1) obtaining a calibrated reference position control signal V 'through the reference position calibration'_yrefAnd a force balance voltage V_a0；

2) Under open-loop control, a force-balancing voltage V is applied to the force-balancing electrode_a0The accelerometer works on the calibrated reference position, and the force balance voltage is generated by a force balance control signal through a push-pull circuit;

3) step-by-step increase of the tuning voltage V_tUntil the open-loop accelerometer has pull-in phenomenon, obtaining critical pull-in voltage V_pi；

4) Will accelerate the speed meterIn a closed loop state and controlling the signal V 'at a reference position'_yrefPlus a frequency of ω_iThe in-bandwidth calibration signal of (3) may be sinusoidal V_yref0 sin(ω_it) or a square wave signal, and setting the tuning voltage to V_t＝αV_piAnd alpha is a voltage coefficient;

5) the force balance control signal fed back by the closed loop is demodulated (the demodulation frequency is omega)_i) Low-pass filtering to obtain voltage signal V representing equivalent stiffness_kref。

6) Obtaining a voltage signal V through rigidity calibration_krefSetting the reference stiffness value, and extracting an updated voltage signal V 'representing equivalent stiffness according to the method in the step 5)'_krefObtaining deviation value through comparison in the controller, obtaining compensation quantity delta V of tuning voltage through proportional, integral and differential operation_tTo the primary comb tuning voltage V_tAbove, thereby maintaining V'_kref＝V_krefI.e. the equivalent stiffness value is always maintained at the reference stiffness value.

It should be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.