Double-loop closed-loop control method for weak coupling resonator

Abstract

The invention provides a double-loop closed-loop control method for a weakly coupled resonator, double loops comprise a first closed-loop and a second closed-loop, the first closed-loop is an amplitude regulation and control loop, the amplitude of a driving signal is adjusted by tracking the amplitude information of a single resonator in the weakly coupled resonator, and the amplitude of the driving signal is adjusted by tracking the amplitude information of the single resonator in the weakly coupled resonator. Therefore, the vibration amplitude of the specified single resonator is kept constant; and the second closed loop is a phase-locked amplifier demodulation loop and is used for tracking the phase and frequency of the other single resonator in the weakly-coupled resonator and adjusting the phase and frequency information of the driving signal so as to maintain the frequency stability of the weakly-coupled resonator. Amplitude, frequency and phase information of the driving signals obtained by the first closed loop and the second closed loop are processed by a frequency mixing link to obtain the driving signal after frequency mixing and the first driving signal. According to the invention, the weak coupling resonator can stably work in any basic resonance mode, and the resolution and precision of the sensor based on the weak coupling resonator can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of MEMS resonator control, and in particular relates to a dual-loop closed-loop control method for a weakly coupled resonator. Background Art

[0002] A weakly coupled resonator is a multi-degree-of-freedom resonator, which is formed by coupling multiple identical single resonators through a connecting structure. The number of degrees of freedom and fundamental resonant modes of this coupled resonator is equal to the number of single resonators. In particular, when the coupling stiffness of the connecting structure is much lower (usually not more than 0.1 times) than the stiffness of the single resonator, this coupled resonator is called a weakly coupled resonator. Weakly coupled resonators are famous for their high sensitivity to stiffness perturbations and micro-mass perturbations, and have been widely used in scenarios such as accelerometers, pressure, and gas detection. Unlike traditional single-degree-of-freedom resonators, which have multiple output quantities (such as frequency, amplitude, and amplitude ratio), the most common amplitude ratio (dividing the vibration amplitudes of the two selected single resonators) is used here as the output quantity.

[0003] Compared with the open-loop control method, the closed-loop control has advantages in convenience, ease of operation and stability. The quality of the closed-loop control technology determines the stability of the frequency and amplitude of the weakly coupled resonator, which affects the key indicators such as the accuracy and resolution of the sensor using such resonators. At present, there are two types of schemes: constant drive based on phase-locked loop and constant frequency drive based on automatic gain control. Yan Zimu et al. described a closed-loop control scheme based on a phase-locked loop in the paper "Research on Electrostatic Field Test Method Based on Modal Localization Effect [D]. Xi'an: Northwestern Polytechnical University, 2020." At this time, the phase-locked loop locks the frequency information according to the phase of the vibration signal of the monomer resonator to generate a constant amplitude drive signal. Because the amplitude of the monomer resonator is not directly controlled in this scheme, the amplitude of each monomer resonator will randomly jitter within a certain range due to the influence of noise, affecting the stability of the final amplitude ratio output. Kang Hao et al. described an automatic gain control method in the paper “Aclosed-loop accelerometer based on three degree-of-freedom weakly coupled resonator [J]. IEEE Sensors Journal, 2018, 18(10): 3960-3967.” The method controls the amplitude of a single resonator to a set value. However, due to the implementation mechanism of this method, the single resonator whose amplitude is controlled to be stable and the single resonator being driven must be the same resonator. In this case, the loop parameters (such as phase) of the closed-loop control Barkhausen conditions for each basic resonant mode are basically the same, resulting in uncontrollable operating modes (such as the in-phase mode and anti-phase mode in a two-degree-of-freedom system). This problem is particularly serious when the frequencies of the basic resonant modes are very close (very common, because such a design is conducive to obtaining high sensitivity characteristics), and the closed loop cannot even be completed.

[0004] According to the above analysis, the closed-loop scheme based on the phase-locked loop is affected by interference factors such as noise, and has the problem of poor amplitude stability of each monomer resonator. The scheme based on automatic gain control cannot distinguish many basic resonant modes well because the monomer resonator with stable amplitude controlled and the driven monomer resonator must be the same, especially when the frequencies of the basic resonant modes are very close, and it may even be impossible to complete closed-loop control. Summary of the invention

[0005] To solve the above technical problems, the present invention provides a dual-loop closed-loop control method for a weakly coupled resonator, which combines a phase-locked loop control method with an automatic gain control method to form a dual-loop solution to achieve closed-loop control of the weakly coupled resonator.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: A dual-loop closed-loop control method for a weakly coupled resonator, the dual loop includes a first closed-loop and a second closed-loop. The first closed-loop is an amplitude control loop, which adjusts the amplitude of a driving signal by tracking the amplitude information of a monomer resonator in the weakly coupled resonator, thereby maintaining the constant vibration amplitude of the specified monomer resonator; the second closed-loop is a phase-locked amplifier demodulation loop, which is used to track the phase and frequency of another monomer resonator in the weakly coupled resonator, adjust the phase and frequency information of the driving signal, thereby maintaining the frequency stability of the weakly coupled resonator. Finally, the driving signals obtained by the first closed-loop and the second closed-loop are processed by a mixing link to obtain a mixed driving signal and a first driving signal.

[0007] Furthermore, the vibration pickup signals of the first closed-loop and the second closed-loop come from different single resonators in the weakly coupled resonator.

[0008] Furthermore, the first driving signal and the vibration pickup signal of the second closed-loop belong to different single resonators in the weakly coupled resonator.

[0009] Furthermore, in the first closed-loop circuit, the vibration pickup signal is taken from the first monomer resonator 1-1, and is sent to the phase-locked loop demodulation module after being processed by the pre-amplifier link. After demodulation, the vibration amplitude Amp of the first monomer resonator 1-1 is obtained, and then the vibration amplitude Amp information is sent to the amplitude controller to obtain the amplitude A of the driving signal.

[0010] Furthermore, in the second closed-loop circuit, the vibration pickup signal is taken from the second monomer resonator 1-2, and is sent to the phase-locked loop demodulation module after being processed by the pre-amplifier link. After demodulation, the vibration frequency and phase of the second monomer resonator 1-2 can be obtained, and then the frequency ω and phase φ information are sent to the phase-frequency controller to obtain the frequency and phase sin(ωt+φ) of the driving signal. The function of the phase-frequency controller is similar to that of a controllable oscillator.

[0011] Furthermore, the amplitude, frequency and phase information of the driving signals obtained by the first closed-loop and the second closed-loop are processed by a mixing link to obtain a driving signal A·sin(ωt+φ) and a first driving signal. The first driving signal is processed by a parameterization link to obtain a second driving signal, which are used to drive the first monomer resonator and the second monomer resonator respectively.

[0012] Furthermore, the parameterization link is a function generator, which converts the first driving signal into the second driving signal according to an arbitrarily set functional relationship.

[0013] Furthermore, the function generator may be a zero-value function, that is, the second driving signal is always zero.

[0014] Furthermore, the closed-loop control is applicable to any weakly coupled resonator, and is only applicable to weakly coupled resonators.

[0015] Furthermore, the weakly coupled resonator refers to a multi-degree-of-freedom resonator composed of at least two monomer resonators with similar or equal first-order modal frequencies through a coupling structure, and the coupling stiffness of the coupling structure is less than 0.1 times the effective stiffness of each monomer resonator, but not zero.

[0016] Beneficial effects: (1) The present invention adopts a two-closed-loop solution, which can make the amplitude signal fluctuation of the weakly coupled resonator smaller than the previous single-loop solution, and helps to improve the resolution, repeatability error and accuracy of the sensor based on the weakly coupled resonator.

[0017] (2) The present invention is conducive to stable closed-loop control when the basic resonant modes are very close to each other (especially when the difference between the frequencies of the basic resonant modes is less than 2 times the bandwidth), thereby maximizing the high sensitivity of the weakly coupled resonator to stiffness disturbances and micro-mass disturbances. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of a dual-loop closed-loop control method for a weakly coupled resonator according to the present invention; Figure 2 This is the structural block diagram of the amplitude controller.

[0019] Among them, the figure markings are: first monomer resonator 1-1, second monomer resonator 1-2, coupling structure 1-3, anchor point 2, first electrostatic electrode 3-1, second electrostatic electrode 3-2, third electrostatic electrode 3-3, fourth electrostatic electrode 3-4, current limiting resistor 4. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] In order to better describe the dual-loop closed-loop control scheme proposed by the present invention, a two-degree-of-freedom weakly coupled resonator is taken as an example and described in detail as follows: like Figure 1As shown, the two-degree-of-freedom weak coupling resonator is composed of a first monomer resonator 1-1, a second monomer resonator 1-2 and a coupling structure 1-3, and each structure is fixed by an anchor point 2. The first monomer resonator 1-1 and the second monomer resonator 1-2 respectively have a first electrostatic electrode 3-1, a second electrostatic electrode 3-2, a third electrostatic electrode 3-3, and a fourth electrostatic electrode 3-4, wherein the first electrostatic electrode 3-1 is used as a driving electrode, the second electrostatic electrode 3-2 and the fourth electrostatic electrode 3-4 are used as capacitive pickup electrodes, and the third electrostatic electrode 3-3 is used as a spare static electrode plate for adjusting the working state (such as sensitivity) of the weak coupling resonator or for providing a driving force for the second monomer resonator 1-2. The first driving signal and the second driving signal are fed through the capacitor C1 and the capacitor C5 to the first electrostatic electrode 3-1 and the third electrostatic electrode 3-3, and the bias voltage is connected to the two-degree-of-freedom weak coupling resonator through the current limiting resistor 4. The current limiting resistor 4 is connected to the end of the first monomer resonator 1-1 that is not connected to the second monomer resonator 1-2 through the anchor point 2. Capacitor C2 and capacitor C4 are used to isolate low-frequency and DC components in the output signal of the capacitive pickup electrode.

[0022] The present invention includes two closed loops: the first closed loop is a loop for controlling the amplitude stability of the first monomer resonator 1-1, and the second closed loop is a phase-locked loop for controlling the frequency stability of the weakly coupled resonator. It is required that the vibration pickup signals of the two closed loops come from different monomer resonators in the weakly coupled resonator, and the first drive signal and the vibration pickup signal of the second closed loop must belong to different monomer resonators. In this way, it is ensured that the weakly coupled resonator requires different loop control parameters (such as phase angle) in each resonant mode to meet the Barkhausen condition, thereby achieving operation in any specified basic resonant mode.

[0023] In the first closed-loop circuit, the vibration pickup signal is taken from the first monomer resonator 1-1, and is sent to the phase-locked loop demodulation module after being processed by the pre-amplifier link. After demodulation, the vibration amplitude Amp of the first monomer resonator 1-1 can be obtained, and then the amplitude Amp information is sent to the amplitude controller to obtain the amplitude A of the driving signal.

[0024] In the second closed-loop circuit, the vibration pickup signal is taken from the second monomer resonator 1-2, and is sent to the phase-locked loop demodulation module after being processed by the pre-amplifier link. After demodulation, the vibration frequency and phase of the amplitude signal of the second monomer resonator 1-2 can be obtained (with the driving signal as the phase zero point), and then the frequency ω and phase φ information are sent to the phase-frequency controller to obtain the frequency and phase sin(ωt+φ) of the driving signal. The function of the phase-frequency controller is similar to that of a controllable oscillator.

[0025] The amplitude, frequency and phase information of the driving signals obtained by the first closed loop and the second closed loop are processed by the mixing link to obtain the final driving signal A·sin(ωt+φ) and the first driving signal. The first driving signal is processed by the parameterization link to obtain the second driving signal, which is used to drive the first monomer resonator 1-1 and the second monomer resonator 1-2 respectively. The parameterization link is a function generator, which converts the first driving signal into the second driving signal according to the set function relationship. In particular, this function can be a zero-valued function, that is, the second driving signal is always zero.

[0026] like Figure 2 As shown, the amplitude controller calculates the error information E by subtracting the obtained amplitude Amp and the set value. Amp , the amplitude A of the driving signal is calculated by the PID controller. The PID controller is a negative feedback controller. When the amplitude Amp is greater than the set value, the PID controller reduces the amplitude A of the driving signal. Conversely, when the amplitude Amp is less than the set value, the PID controller increases the amplitude A of the driving signal.

[0027] Preferably, the phase-locked loop demodulation module can be an XOR phase-locked loop, an orthogonal phase-locked loop, or an improved version of various basic phase-locked loop demodulation modes.

[0028] Preferably, the present invention is applicable to weakly coupled resonators of various degrees of freedom, not limited to the two-degree-of-freedom weakly coupled resonator in the above example. When the degree of freedom is greater than two, the monomer resonators corresponding to the vibration pickup signals in the first closed loop and the second closed loop can be any two monomer resonators in the weakly coupled resonator.

[0029] The present invention is only applicable to weakly coupled resonators. Here, weakly coupled resonators refer to multi-degree-of-freedom resonators composed of multiple (not less than 2) monomer resonators with similar first-order modal frequencies through a coupling structure. The coupling structure is any structure that connects the above multiple monomer resonators together, and the coupling stiffness of the coupling structure is less than 0.1 times the effective stiffness of the above multiple monomer resonators.

[0030] Preferably, the phase-locked loop demodulation, amplitude calculation, and amplitude / phase controller can be implemented by a programmable logic controller, a digital circuit, an analog circuit, or a combination of the above three.

Claims

1. A dual-loop closed-loop control method for a weakly coupled resonator, characterized in that: The dual loop includes a first closed loop and a second closed loop, wherein the first closed loop is an amplitude control loop, which adjusts the amplitude of the driving signal by tracking the amplitude information of a single resonator in the weakly coupled resonator, thereby maintaining the constant vibration amplitude of the specified single resonator; The second closed loop is a phase-locked amplifier demodulation loop, which is used to track the phase and frequency of another monomer resonator in the weakly coupled resonator, adjust the phase and frequency information of the drive signal, and thus maintain the frequency stability of the weakly coupled resonator. Finally, the amplitude, frequency, and phase information of the drive signal obtained by the first closed loop and the second closed loop are processed by the mixing link to obtain the mixed drive signal and the first drive signal.

2. A dual-loop closed-loop control method for a weakly coupled resonator according to claim 1, characterized in that: The pickup signals of the first closed-loop and the second closed-loop come from different single resonators in the weakly coupled resonator.

3. A dual-loop closed-loop control method for a weakly coupled resonator according to claim 2, characterized in that: The first driving signal and the vibration pickup signal of the second closed-loop belong to different single resonators in the weakly coupled resonator.

4. A dual-loop closed-loop control method for a weakly coupled resonator according to claim 1, characterized in that: In the first closed-loop circuit, the vibration pickup signal is taken from the first monomer resonator 1-1, and is sent to the phase-locked loop demodulation module after being processed by the pre-amplifier link. After demodulation, the vibration amplitude Amp of the first monomer resonator 1-1 is obtained, and then the vibration amplitude Amp information is sent to the amplitude controller to obtain the amplitude A of the driving signal.

5. A dual-loop closed-loop control method for a weakly coupled resonator according to claim 4, characterized in that: In the second closed-loop circuit, the vibration pickup signal is taken from the second monomer resonator 1-2, and is sent to the phase-locked loop demodulation module after being processed by the pre-amplifier link. After demodulation, the vibration frequency and phase of the second monomer resonator 1-2 can be obtained, and then the frequency ω and phase φ information are sent to the phase-frequency controller to obtain the frequency and phase sin(ωt+φ) of the driving signal.

6. A dual-loop closed-loop control method for a weakly coupled resonator according to claim 5, characterized in that: The amplitude, frequency and phase information of the driving signals obtained by the first closed-loop and the second closed-loop are processed by the mixing link to obtain the driving signal A·sin(ωt+φ) and the first driving signal. The first driving signal is processed by the parameterization link to obtain the second driving signal, which are used to drive the first monomer resonator and the second monomer resonator respectively.

7. A dual-loop closed-loop control method for a weakly coupled resonator according to claim 6, characterized in that: The parameterization link is a function generator, which converts the first driving signal into the second driving signal according to an arbitrarily set functional relationship.

8. A dual-loop closed-loop control method for a weakly coupled resonator according to claim 1, characterized in that: Applicable to closed-loop control of any weakly coupled resonator, and only to weakly coupled resonators.

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