CN118566535A - Electrostatic modulation method for capacitive accelerometer - Google Patents
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Abstract
The invention relates to the technical field of accelerometers and discloses an electrostatic modulation method for a capacitive accelerometer. Wherein the method comprises the following steps: a modulating electrode T opposite to the mass block M is arranged in the capacitive accelerometer; applying an alternating current modulation voltage V T to the modulation electrode T to generate an electrostatic spring effect; after the electrostatic spring effect is generated, the output of the capacitive accelerometer is used as the input of the displacement detection circuit, and the detection displacement V M is obtained by the output; taking the detected displacement V M and the given displacement V d as inputs of a force feedback controller G C, outputting to obtain a force feedback signal, and feeding back the force feedback signal to a capacitive accelerometer as inputs; the force feedback signal is monitored and demodulated in real time through a demodulation module; when the elastic force exists in the demodulation result, the given displacement V d is automatically adjusted through the PI adjusting module, the adjusted displacement is obtained, and the adjusted displacement and the detected displacement V M are used as the input of the force feedback controller G C until the elastic force does not exist in the demodulation result.
Description
Technical Field
The invention relates to the technical field of accelerometers, in particular to an electrostatic modulation method for a capacitive accelerometer.
Background
The basic principle of the micro-electromechanical capacitive accelerometer is that a narrow-band capacitive detection circuit is used for detecting inertial force and corresponding in-plane micro displacement caused by external acceleration on a mass block M, and a measurement and control circuit design thereof selects an open-loop working mode and a closed-loop working mode according to performance index requirements and circuit complexity. The closed loop control mode includes a ΣΔ mode and a position servo mode. The closed loop force feedback in servo mode uses electrostatic forces to counteract inertial forces on the mass due to external accelerations, inhibiting mass displacement. The acceleration may be calculated from a feedback control voltage required to counteract the inertial force. Advantages of the closed loop mode of operation include improved output linearity, dynamic range, zero offset stability, and other performance metrics. The zero offset stability is an important index for measuring the performance of the accelerometer, and has more influence factors, wherein the influence of the change of the ambient temperature on the zero offset stability is most obvious. The temperature change affects the calibration factor and zero bias stability of the accelerometer by affecting the spring rate of the detection structure, the displacement detection capacitance, and the electrostatic force feedback capacitance.
In an ideal situation, the input of the force feedback controller G C is the micro displacement signal V M of the mass obtained by the capacitive detection circuit, if the gain of G C is high enough, the mass displacement is zero when the closed loop force feedback control loop reaches equilibrium, and the electrostatic feedback force completely counteracts the inertial force. In non-ideal state, due to structural processing error of the accelerometer, the capacitance between the mass block M and the upper and lower polar plates A, B is asymmetric, and the gain of the capacitive detection circuit is unbalanced, under the static condition that the force feedback completely counteracts the inertia force, the displacement detection circuit still outputs a non-zero value, so that the force feedback control link outputs corresponding electrostatic force, and the mass block deviates from an ideal balance position against the supporting spring of the mass block. Thus, in the presence of external accelerations, the force feedback not only counteracts the inertial forces, but also includes elastic forces due to structural and circuit errors. This part of the spring force constitutes a part of the output null of the accelerometer.
As the temperature changes the spring rate of the accelerometer structural material changes, the small amount of elastic force contained in the accelerometer force feedback output also fluctuates with the temperature changes, thereby affecting zero bias stability. In order to reduce the effect of temperature changes on the zero bias stability of the capacitive accelerometer, the electrostatic force applied by the force feedback controller should only counteract the inertial force associated with external acceleration while avoiding the occurrence of elastic forces in the force feedback when designing the measurement and control circuitry of the accelerometer. However, this object is not achieved by the prior art.
Disclosure of Invention
The invention provides an electrostatic modulation method for a capacitive accelerometer, which can solve the technical problems in the prior art.
The invention provides an electrostatic modulation method for a capacitive accelerometer, wherein the method comprises the following steps:
A modulating electrode T opposite to the mass block M is arranged in the capacitive accelerometer;
Applying an alternating current modulation voltage V T to the modulation electrode T to generate an electrostatic spring effect;
After the electrostatic spring effect is generated, the output of the capacitive accelerometer is used as the input of the displacement detection circuit, and the detection displacement V M is obtained by the output;
Taking the detected displacement V M and the given displacement V d as inputs of a force feedback controller G C, outputting to obtain a force feedback signal, and feeding back the force feedback signal to a capacitive accelerometer as inputs;
The force feedback signal is monitored and demodulated in real time through a demodulation module;
When the elastic force exists in the demodulation result, the given displacement V d is automatically adjusted through the PI adjusting module, the adjusted displacement is obtained, and the adjusted displacement and the detected displacement V M are used as the input of the force feedback controller G C until the elastic force does not exist in the demodulation result.
Preferably, the output of the capacitive accelerometer is used as an input of a displacement detection circuit, and the obtaining the detected displacement V M from the output includes:
Applying a positive carrier signal Asinωt and a negative carrier signal-Asinωt on an upper electrode A and a lower electrode B of the mass M respectively, and simultaneously applying a force feedback control signal V F and a bias voltage V B on the upper electrode A and the lower electrode B to generate a force feedback controlled electrostatic force F E to counteract an external inertial force, wherein A is a carrier signal amplitude, and ω is a carrier frequency;
Converting the output of the capacitive accelerometer into a displacement signal by using an amplifying unit;
the converted displacement signal is demodulated by a demodulator through a carrier signal sin omega t, and the detection displacement V M is obtained through output.
Preferably, the applied ac modulation voltage V T is:
VT＝VsinωTt,
wherein V is the voltage amplitude, and omega T is the modulation frequency of the electrostatic spring.
Preferably, the electrostatic spring effect is generated:
KE＝γVT 2(1-cos2ωTt)，
where K E is the equivalent electrostatic spring constant and γ is the modulation constant.
Preferably, the generated force feedback controlled electrostatic force F E is:
FE＝4βVFVB，
where β is the electrostatic force feedback gain constant.
Preferably, the amplifying unit includes a charge amplifier and a displacement detection capacitor C F.
Through the above technical scheme, the supporting spring K of the mass block M of the accelerometer can be subjected to alternating current modulation through the electrostatic spring effect, and specifically: (1) An additional electrode T is added in the microstructure of the accelerometer, and the voltage difference between the electrode T and the mass M generates an electrostatic spring effect, so that the effective spring coefficient of the supporting spring K of the mass is changed. (2) By modulating the ac electrostatic spring, the dc elastic force kx that may be present in the force feedback is modulated accordingly to a higher ac modulation frequency ω T; and then analyzing whether the modulation frequency component exists in the force feedback output, so that whether the elastic force exists in the force feedback can be detected in real time. (3) Adjusting a given displacement V d of the force feedback controller may change the operating point of the force feedback. (4) The modulation frequency component in the force feedback output is used as the automatic adjustment control input of the working point V d of the servo control loop of the position of the force feedback mass block after synchronous demodulation; and V d is regulated in a closed loop mode until the output of the synchronous demodulation link is zero, and the force feedback does not contain elastic force. In other words, the high-frequency modulation can be performed on the spring coefficient, whether the elastic force exists in the force feedback or not can be detected in real time, and meanwhile, the elastic force is eliminated in the force feedback output, so that the purpose of improving the zero-bias stability of the accelerometer is achieved.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. It is evident that the drawings in the following description are only some embodiments of the present invention and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.
FIG. 1 shows a functional block diagram of an electrostatic modulation method for a capacitive accelerometer according to embodiments of the invention;
FIG. 2 shows a schematic diagram for a capacitive accelerometer according to embodiments of the invention;
fig. 3 shows a functional block diagram of a displacement detection circuit according to an embodiment of the invention.
Detailed Description
It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other. The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the application, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
The relative arrangement of the components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless it is specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective parts shown in the drawings are not drawn in actual scale for convenience of description. Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but should be considered part of the specification where appropriate. In all examples shown and discussed herein, any specific values should be construed as merely illustrative, and not a limitation. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further discussion thereof is necessary in subsequent figures.
As shown in fig. 1 and 3, an embodiment of the present invention provides an electrostatic modulation method for a capacitive accelerometer, where the method includes:
A modulating electrode T opposite to the mass block M is arranged in the capacitive accelerometer;
wherein, the mass M and the modulating electrode T form a modulating capacitor, and the size of the capacitor is negligible.
Applying an alternating current modulation voltage V T to the modulation electrode T to generate an electrostatic spring effect;
After the electrostatic spring effect is generated, the output of the capacitive accelerometer is used as the input of the displacement detection circuit, and the detection displacement V M is obtained by the output;
Taking the detected displacement V M and the given displacement V d as inputs of a force feedback controller G C, outputting to obtain a force feedback signal, and feeding back the force feedback signal to a capacitive accelerometer as inputs;
The force feedback signal and the inertial force (f=ma) are calculated by an adder and then used as the input of an accelerometer, and the detected displacement V M and the given displacement V d are calculated by an adder and then used as the input of a force feedback controller G C.
The force feedback signal is monitored and demodulated in real time through a demodulation module;
When the elastic force exists in the demodulation result, the given displacement V d is automatically adjusted through the PI adjusting module, the adjusted displacement is obtained, and the adjusted displacement and the detected displacement V M are used as the input of the force feedback controller G C until the elastic force does not exist in the demodulation result.
Through the above technical scheme, the supporting spring K of the mass block M of the accelerometer can be subjected to alternating current modulation through the electrostatic spring effect, and specifically: (1) An additional electrode T is added in the microstructure of the accelerometer, and the voltage difference between the electrode T and the mass M generates an electrostatic spring effect, so that the effective spring coefficient of the supporting spring K of the mass is changed. (2) By modulating the ac electrostatic spring, the dc elastic force kx that may be present in the force feedback is modulated accordingly to a higher ac modulation frequency ω T; and then analyzing whether the modulation frequency component exists in the force feedback output, so that whether the elastic force exists in the force feedback can be detected in real time. (3) Adjusting a given displacement V d of the force feedback controller may change the operating point of the force feedback. (4) The modulation frequency component in the force feedback output is used as the automatic adjustment control input of the working point V d of the servo control loop of the position of the force feedback mass block after synchronous demodulation; and V d is regulated in a closed loop mode until the output of the synchronous demodulation link is zero, and the force feedback does not contain elastic force. In other words, the high-frequency modulation can be performed on the spring coefficient, whether the elastic force exists in the force feedback or not can be detected in real time, and meanwhile, the elastic force is eliminated in the force feedback output, so that the purpose of improving the zero-bias stability of the accelerometer is achieved.
In fig. 3, a capacitive MEMS accelerometer structure is shown, in which a mass M is in the middle and is coupled to two fixed support anchors by springs K, and inertial forces caused by external acceleration cause a small displacement of the mass in the in-plane lateral direction. The displacement of the mass M is detected by the two groups of electrodes A and B, and simultaneously, the required electrostatic force can be applied to the mass by the electrodes A and B to form force feedback control. The modulating electrode T provides electrostatic spring modulation to cause the support spring coefficient K of the mass M to alternate at a frequency of 2ω T.
According to one embodiment of the present invention, as shown in fig. 2, the output of the capacitive accelerometer is used as an input of the displacement detection circuit, and the output to obtain the detected displacement V M includes:
Applying a positive carrier signal Asinωt and a negative carrier signal-Asinωt on an upper electrode A and a lower electrode B of the mass M respectively, and simultaneously applying a force feedback control signal V F and a bias voltage V B on the upper electrode A and the lower electrode B to generate a force feedback controlled electrostatic force F E to counteract an external inertial force, wherein A is a carrier signal amplitude, and ω is a carrier frequency;
Converting the output of the capacitive accelerometer into a displacement signal by using an amplifying unit;
The converted displacement signal is demodulated (synchronous demodulation, narrow-band detection of the micro displacement of the mass block is formed) by a Demodulator (DEMO) through a carrier signal sin omega t, and the detection displacement V M is output.
In fig. 2, C1 represents the capacitance formed by the upper electrode a and the mass, and C2 represents the capacitance formed by the lower electrode B and the mass.
According to one embodiment of the invention, the applied ac modulation voltage V T is:
VT＝VsinωTt,
wherein V is the voltage amplitude, and omega T is the modulation frequency of the electrostatic spring.
By applying a modulating voltage, a cos2ω T t modulation of the spring constant is formed.
According to one embodiment of the invention, the electrostatic spring effect is generated:
KE＝γVT 2(1-cos2ωTt)，
Where K E is the equivalent electrostatic spring coefficient (i.e., the equivalent electrostatic spring coefficient of the support spring K), and γ is the modulation constant (which is related to the size of the modulation electrode).
Because the force feedback deviates the mass from the equilibrium position, x+.0, the force feedback F contains a 2-fold frequency component: f= [ k+γv T 2(1-cos2ωT t) ] x+ m a, x is the spring deflection, and ma is the inertial force. It can be determined whether the elastic force is included in the force feedback. In order not to affect the proper operation of the accelerometer, the electrostatic spring modulation frequency ω T may be higher than the design bandwidth of the accelerometer.
And 2 omega T elastic force components in force feedback output are monitored in real time through a demodulation link, and the given displacement V d of the force feedback is correspondingly regulated, so that the regulated displacement tracks the V M value of the mass block in a static state in real time. Due to the high gain of the PI link, when the system reaches a stable state, elastic force does not exist in force feedback any more, and the elimination of the elastic force is realized.
According to one embodiment of the present invention, the generated force feedback controlled electrostatic force F E is:
FE＝4βVFVB，
where β is the electrostatic force feedback gain constant, which may be determined by the geometry of the force feedback electrode.
According to one embodiment of the present invention, as shown in fig. 2, the amplifying unit includes a charge amplifier and a displacement detection capacitor C F.
In the description of the present invention, it should be understood that the azimuth or positional relationships indicated by the azimuth terms such as "front, rear, upper, lower, left, right", "lateral, vertical, horizontal", and "top, bottom", etc., are generally based on the azimuth or positional relationships shown in the drawings, merely to facilitate description of the present invention and simplify the description, and these azimuth terms do not indicate and imply that the apparatus or elements referred to must have a specific azimuth or be constructed and operated in a specific azimuth, and thus should not be construed as limiting the scope of protection of the present invention; the orientation word "inner and outer" refers to inner and outer relative to the contour of the respective component itself.
Spatially relative terms, such as "above … …," "above … …," "upper surface on … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial location relative to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or structures would then be oriented "below" or "beneath" the other devices or structures. Thus, the exemplary term "above … …" may include both orientations "above … …" and "below … …". The device may also be positioned in other different ways (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
In addition, the terms "first", "second", etc. are used to define the components, and are only for convenience of distinguishing the corresponding components, and the terms have no special meaning unless otherwise stated, and therefore should not be construed as limiting the scope of the present invention.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (6)
1. An electrostatic modulation method for a capacitive accelerometer, the method comprising:
A modulating electrode T opposite to the mass block M is arranged in the capacitive accelerometer;
Applying an alternating current modulation voltage V T to the modulation electrode T to generate an electrostatic spring effect;
After the electrostatic spring effect is generated, the output of the capacitive accelerometer is used as the input of the displacement detection circuit, and the detection displacement V M is obtained by the output;
Taking the detected displacement V M and the given displacement V d as inputs of a force feedback controller G C, outputting to obtain a force feedback signal, and feeding back the force feedback signal to a capacitive accelerometer as inputs;
The force feedback signal is monitored and demodulated in real time through a demodulation module;
When the elastic force exists in the demodulation result, the given displacement V d is automatically adjusted through the PI adjusting module, the adjusted displacement is obtained, and the adjusted displacement and the detected displacement V M are used as the input of the force feedback controller G C until the elastic force does not exist in the demodulation result.
2. The method of claim 1, wherein the output of the capacitive accelerometer as an input to the displacement detection circuit, the output resulting in the detected displacement V M comprises:
Applying a positive carrier signal Asinωt and a negative carrier signal-Asinωt on an upper electrode A and a lower electrode B of the mass M respectively, and simultaneously applying a force feedback control signal V F and a bias voltage V B on the upper electrode A and the lower electrode B to generate a force feedback controlled electrostatic force F E to counteract an external inertial force, wherein A is a carrier signal amplitude, and ω is a carrier frequency;
Converting the output of the capacitive accelerometer into a displacement signal by using an amplifying unit;
the converted displacement signal is demodulated by a demodulator through a carrier signal sin omega t, and the detection displacement V M is obtained through output.
3. The method according to claim 2, wherein the applied ac modulation voltage V T is:
VT＝VsinωTt,
wherein V is the voltage amplitude, and omega T is the modulation frequency of the electrostatic spring.
4. A method according to claim 3, characterized in that the electrostatic spring effect is generated:
KE＝γVT 2(1-cos2ωTt)，
where K E is the equivalent electrostatic spring constant and γ is the modulation constant.
5. The method of claim 4, wherein the generated force feedback controlled electrostatic force F E is:
FE＝4βVFVB，
where β is the electrostatic force feedback gain constant.
6. The method according to any of claims 2-5, wherein the amplifying unit comprises a charge amplifier and a displacement detection capacitance C F.
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