CN114894173A - A mass stiffness decoupling ring MEMS resonator structure and trimming method - Google Patents

Abstract

The invention discloses a mass stiffness decoupling ring type MEMS resonator structure and a trimming method. The mass stiffness decoupling ring type MEMS resonator structure comprises an anchor point, a resonance ring and a supporting beam positioned between the anchor point and the resonance ring, wherein raised mass blocks are uniformly distributed in the circumferential direction of the resonance ring. According to the invention, the mode of adding the raised mass block on the resonance ring is adopted, the mass rigidity decoupling of the harmonic oscillator is realized, the equivalent vibration mass of the system is improved, the frequency of the system is reduced, the mode trimming of the harmonic oscillator can be quickly realized, and the aims of improving the sensitivity, the resolution ratio, the signal-to-noise ratio and the like of the system are finally achieved.

Description

A mass stiffness decoupling ring MEMS resonator structure and trimming method

technical field

The invention relates to the technical field of resonators, and more particularly, to a mass stiffness decoupling ring type MEMS resonator structure and a trimming method.

Background technique

Frequency cracking is a stumbling block on the road to the development of high-performance gyroscopes. Frequency cracking will seriously affect the sensitivity, resolution, and signal-to-noise ratio of gyroscopes. The adjustment of the ring gyro has always been a major topic of concern in the research field. Many research institutions are constantly exploring the design or adjustment methods of new structures to solve the problem of modal mismatch caused by machining errors. The Chinese invention patent with the patent number of ZL201910811367.4 proposes to remove the mass block by the method of laser trimming at the corresponding position inside the resonant ring, and change the stiffness mismatch of the gyro drive axis and the detection axis. In the traditional mechanical trimming process, the ring MEMS gyroscope can only remove or add mass on the ring, which will affect the mass and stiffness distribution of the gyro resonator at the same time, making the trimming process too cumbersome and difficult. Therefore, it is necessary to design a mass stiffness decoupling ring MEMS resonator structure and a tuning method.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a mass-stiffness decoupling ring MEMS resonator structure and a trimming method, so as to overcome the defects existing in the prior art.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A mass stiffness decoupling ring type MEMS resonator structure includes an anchor point, a resonant ring, and a support beam between the anchor point and the resonant ring, and the resonant ring has raised mass blocks uniformly distributed in the circumferential direction.

Further, the number of the mass blocks is a multiple of 8.

Further, the mass is any structure with mass.

Further, the uniform distribution of the mass blocks in the circumferential direction of the resonant ring satisfies the condition of rotational symmetry.

The present invention also provides a method for adjusting the above-mentioned mass-stiffness decoupling ring MEMS resonator structure, comprising the following steps:

S1. The frequency sweep test determines the frequency cracking, and judges the position of the low frequency rigid axis;

S2. Select the mass block closest to the rigid axis to start trimming, and monitor whether the rigid axis is aligned in real time;

S3. After the rigid axis is aligned, the two mass blocks aligned with the rigid axis are adjusted at the same time by the same amount until the frequency difference reaches the set requirement.

Further, the step S1 is specifically realized by the following methods:

Connect the signal input and output end of the lock-in amplifier to the output and input end of the gyro signal, and excite the resonator through the power supply to measure the phase and amplitude of the signal at the gyro drive shaft end.

If there are two peaks in the amplitude signal, the rigid axis has a certain deflection angle, the abscissa corresponding to the peak is the frequency value of the mode, and the difference between the two abscissas is the frequency cracking value;

If the amplitude signal has only one peak value, the rigid axis has been aligned, and the frequency sweep is continued by replacing another rigid axis, and the frequency difference between the two frequency sweeps is the frequency cracking value.

Further, the trimming method in the step S2 includes point-type addition of conductive glue, femtosecond laser removal of the mass block or addition of the mass block; if the point-type addition of the conductive glue is used, the position of the high-frequency rigid axis determined in step S1 is used, Determine the mass block closest to the high-frequency rigid axis for dispensing; if the mass is removed by femtosecond laser, the position of the low-frequency rigid axis determined in step S1 is used to determine the mass block closest to the high-frequency rigid axis for drilling.

Further, in the step S3, the two mass blocks whose rigid axes are aligned at the same time are trimmed at the same time, including point-wise adding conductive glue to increase the mass block or femtosecond laser to remove the mass block; if the femtosecond laser is used for frequency modulation, Confirm that the two mass blocks corresponding to the low-frequency rigid axis are punched at the same time.

Further, the trimming also includes a combination of removing mass and increasing mass, and a combination of mass blocks.

Further, the trimming also includes a balance trimming, and the balance trimming includes removing or adding the same mass at the four equivalent symmetrical positions at the same time.

Compared with the prior art, the present invention has the advantages that the present invention provides a mass-stiffness decoupling ring type MEMS resonator structure and a trimming method, in which a raised mass block is added to the resonant ring to realize resonance. The decoupling of the mass stiffness of the harmonic oscillator improves the equivalent vibration quality of the system, while reducing the frequency of the system, which can quickly realize the modal adjustment of the harmonic oscillator, and finally achieve the goals of improving the sensitivity, resolution and signal-to-noise ratio of the system. The combined adjustment is convenient and flexible, the adjustment position is easy to determine and the balance adjustment is used.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

1 is a schematic structural diagram of a mass-stiffness decoupling ring-type MEMS resonator of the present invention;

Fig. 2 is the topological structure diagram of the harmonic oscillator of mass stiffness decoupling of the present invention;

3 is a schematic diagram of the first mode and the second mode of the harmonic oscillator with mass stiffness decoupling according to the present invention;

FIG. 4 is a schematic diagram of the combined tuning of the harmonic oscillator with mass stiffness decoupling according to the present invention;

5 is a schematic diagram of a method for trimming a ring-type MEMS sensitive structure with mass-stiffness decoupling according to the present invention;

FIG. 6 is a schematic diagram of a modal mismatch error based on quadrature detection according to the present invention.

Detailed ways

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, and the protection scope of the present invention can be more clearly defined.

Referring to FIG. 1 and FIG. 2 , the present embodiment discloses a mass-stiffness decoupling ring type MEMS resonator structure. The overall frame is of an all-around anchored type, including an anchor point 100 , a resonant ring 200 , and an anchor point 100 . A typical embodiment of the support beam 300 between the vibrating rings 200 is shown in FIG. 1 , the protruding mass blocks 400 are evenly distributed in the circumferential direction of the resonating ring, which can realize the decoupling effect of mass and stiffness, that is, using femtosecond laser or Other mechanical tuning methods change the mass on the raised mass only to affect the mass distribution of the structure without affecting the stiffness of the structure.

In some embodiments, the beam width and thickness of the gyro resonator and the angle of the protruding mass can also be designed according to the needs of a specific use environment, and changing these parameters will affect the final performance of the gyro. In other embodiments, the number and shape of the protruding proof-mass can be changed, and its topology is shown in FIG. 2 .

In this embodiment, the number of the quality blocks is a multiple of 8, which may be 8, 16, or the like.

In this embodiment, the mass block is any structure with mass, and the shape is not limited.

In this embodiment, the uniform distribution of the mass blocks in the circumferential direction of the resonant ring satisfies the condition of rotational symmetry.

The ring MEMS gyroscope works in n=2 modes, and the included angle between the first mode and the second mode's inherent rigidity axis is 45°, as shown in FIG. 3 .

As shown in Figure 4, the raised mass blocks are numbered in sequence, 1 to 16, respectively. During the trimming process, different matching methods are selected for trimming according to actual needs. According to the trimming theory, the trimming effect is equivalent on the protruding mass blocks separated by 90°. When the balance adjustment is not considered, when the high-frequency rigid axis is directly facing the center of the No. 1 raised mass block, the shaft adjustment can be performed only on No. 1; when the deflection of the high-frequency rigid axis is small, such as between No. 1 and No. 16 During the period, you can adjust the shaft alignment by adjusting the mass block closest to the axis, and then continue to adjust the frequency on No. 1 and No. 16 or No. 2 and No. 3 at the same time; when the deflection angle of the high-frequency rigid shaft is large, such as between No. 1 and No. 1 Between No. 2, you can adjust the axis alignment on the two mass blocks at the same time and continue to adjust the frequency on No. 1 and No. 16 or No. 2 and No. 3 at the same time. When considering balance trim, changing the mass on one raised mass must simultaneously change the same mass on the masses that are 90° or 180° apart. For example, trimming can be performed on No. 1 and No. 9 or No. 1, No. 5, No. 9 and No. 13 at the same time according to the initial frequency cracking and the deflection angle of the high-frequency rigid shaft. In the process of shaft adjustment, instead of selecting a certain combination of mass blocks, the selected mass blocks can be changed in time according to the change of the deflection direction of the high-frequency rigid shaft, that is, the shaft can be adjusted flexibly and quickly. For example, when the deflection angle of the high-frequency rigid shaft is large, adjust the shaft on No. 1 and No. 2, but during this process, the high-frequency rigid shaft will be slowly aligned, that is, the deflection angle will gradually become smaller, and then it can only continue on No. 1 in due course. Adjust the shaft. Combined continuous trimming is not only a combination of raised masses, but also a combination of trimming methods. For example, it might be possible to tune the axis by removing mass on number 1, while adding mass on numbers 2 and 3 for frequency tuning.

The trimming method of this embodiment utilizes the femtosecond laser to remove the mass to achieve frequency matching of the ring-type MEMS sensitive structure. For femtosecond laser removal quality adjustment, it is necessary to locate the high-frequency rigid axis with a lower frequency, so as to increase the frequency corresponding to the high-frequency rigid axis and reduce the frequency difference. The use of femtosecond laser to remove the mass on the raised mass must ensure that the overall structure of the resonator is not excessively damaged, that is, the removed mass must have a certain limit. Generally, the overall mass of the raised mass designed in this embodiment is equal to 1/10 is the principle. The position of mass removal can be selected from the center of the raised mass block or other positions. Due to the decoupling of mass stiffness, the distribution of structural stiffness will not be affected. According to the use characteristics of femtosecond laser equipment, the removal mass is usually punched in the shape of a cylinder, and the center of the raised mass is used as the center of the circle to extend to the periphery. The amount of mass removed depends on the deflection angle of the high-frequency rigid axis and the size of the frequency cracking to select the size of the femtosecond laser path and the drilling depth.

The general idea of the adjustment method for the ring-type MEMS sensitive structure of the present invention is to adjust the shaft first and then adjust the frequency. In the process of adjusting the shaft, the key is to accurately identify the alignment problem of the rigid shaft. As shown in Figure 5, among the three position lines, the 17th and 18th lines are separated by 45°, and the 19th line is the angle bisector of the two. Used to describe the position of the rigid axis during the trimming process. The initial rigid axis deflection angle of the resonator ranges from 0 to 22.5° (assuming that the rigid axis is deviated to the right). The angle difference between the drive shaft and the detection shaft of the resonator is 45°, and the angle between the centers of the protruding mass blocks is 22.5°. It can be seen that the rigid axis may deviate from the originally aligned two protruding mass blocks. In order to minimize the introduction of unstable error factors during gyro trimming, the trimming masses should be symmetrically distributed. The modal mismatch error identification in the tuning method of the present invention is mainly based on quadrature detection. As shown in FIG. 6 , due to the deflection of the rigid axis, the driving axis and the detection axis of the gyro resonator are excited at the same time, and a quadrature signal is generated. . The sinusoidal component in the quadrature signal corresponds to the frequency difference caused by the deflection of the rigid shaft, so it can be judged whether the rigid shaft is aligned.

Taking a rosette-type resonator as an example, the method for adjusting the mass-stiffness decoupling ring-type MEMS resonator structure of the present embodiment includes the following steps:

Step S1, the frequency sweep test determines the frequency cracking, and judges the position of the low frequency rigid axis.

Specifically, a lock-in amplifier signal input and output end is connected to the gyro signal output and input end, and the phase and amplitude of the signal can be measured at the gyro drive (or detection) shaft end by exciting the resonator through the power supply. If there are two peaks in the amplitude signal, it means that the rigid axis has a certain deflection angle, the abscissa corresponding to the peak is the frequency value of the mode, and the difference between the two abscissas is the frequency cracking value; if the amplitude signal has only one peak , it means that the rigid axis has been aligned, and then continue to sweep the frequency by changing to another axis, and the frequency difference between the two sweeps is the frequency cracking value. Due to the symmetrical structure, as shown in Figure 5, the black lines 17 and 18 are the corresponding positions of the drive shaft and the detection shaft under ideal conditions, and the included angle is 45°. Assuming that the rigid axis is deviated to the right, it can be determined that the low frequency rigid axis is roughly between 17 and 19 or 18 and 19 according to the position of the driving or detection electrode and the frequency of the sweep frequency. In general, the initial frequency of the harmonic oscillator is split to several tens of Hz, and the angle between the rigid axis and the ideal position is within 11.25°.

Step S2, select the mass block closest to the rigid axis to start trimming, and monitor whether the rigid axis is aligned in real time.

Specifically, the main purpose of this step is to adjust the rigid axis to an ideal position, and the adjustment methods adopted can include: point-wise addition of conductive glue, and femtosecond laser to remove quality. Among them, the point-type addition of conductive adhesive belongs to the adjustment method for increasing the quality. According to the relationship between frequency and quality, the position of the high-frequency rigid axis is determined through step S1, and the protruding mass block closest to the high-frequency rigid axis is found for dispensing; Second laser removal quality belongs to the adjustment method of removal quality. The position of the low frequency rigid axis is determined through step S1, and the protruding mass block closest to the high frequency rigid axis is found for drilling.

The simplified second-order dynamic equation of the ring MEMS gyro resonator is:

Among them, m is the equivalent mass, c ₁ and c ₂ are the equivalent damping, k ₁ and k ₂ are the equivalent stiffness, the x-direction is the driving mode, and the y-direction is the detection mode. In the ideal case, the driving force f is directly opposite the driving shaft, the driving frequency is w _d , and an angular velocity in the z direction is applied in the plane, and Ag is the angular _gain .

As shown in Fig. 6, due to the deflection of the rigid axis, the driving axis and the detection axis of the gyro resonator are excited at the same time, generating a quadrature signal. According to the above formulas (1) and (2), the expression of the quadrature signal can be obtained as:

Among them, K is the relevant coefficient of the control system. In the expression of the mass block detection modal displacement, only the in-phase component with the driving modal displacement contains the angular velocity Ω _z information. It can be seen from Equation 3 that when the sinusoidal component of the quadrature error signal is zero, the deflection angle of the stiffness axis, that is, θ _w , is zero.

In the process of axis adjustment and adjustment, the output signal end of the gyro can be connected to an oscilloscope accordingly, and whether the sine component of the quadrature signal is zero is monitored in real time to determine whether the axis is aligned. In order to make the trimming effect more beneficial, trimming should not be performed only on one raised mass, but equal trimming should be performed on symmetrical positions.

Step S3: After the rigid axis is aligned, trim and adjust the two mass blocks aligned with the rigid axis at the same time until the frequency difference reaches the set requirement.

Specifically, after the rigid alignment, that is, the adjustment of the axis, the purpose of this step is to perform frequency adjustment. There are two convex masses corresponding to the rigid axis, which is consistent with the adjustment method used in step S2. For example, when using femtosecond laser for frequency modulation, find two convex masses corresponding to the low-frequency rigid axis, and punch holes on them at the same time. . In order to determine when the frequency modulation is over, the lock-in amplifier must be used in real time to observe the frequency sweep of the axis changing. When the frequency sweeping of the changing axis meets the index requirements, the frequency modulation can be considered to be over, and the same amount of adjustment should be carried out at the symmetrical position.

Table 1 Typical parameters of a rosette MEMS gyro resonator model

Table 2 Influence of the modified position and shape (consistent quality) on the raised mass block

This embodiment adopts the method of adding a raised mass block on the resonant ring to realize the decoupling of the mass stiffness of the resonator, improve the equivalent vibration quality of the system, and reduce the frequency of the system at the same time, and can quickly realize the modal modification of the resonator. Adjustment, and ultimately achieve the goal of improving system sensitivity, resolution and signal-to-noise ratio. The simulation results show that under the model parameters shown in Table 1, the influence of the shape and position of the convex mass block on the tuning ability of the harmonic oscillator is shown in Table 2. Removing the same mass on the raised mass, changing the position or shape has no effect on the tuning effect of the harmonic oscillator, and the frequency difference value is the same.

Although the embodiments of the present invention are described in conjunction with the accompanying drawings, the patent owner can make various changes or modifications within the scope of the appended claims, as long as the protection scope described in the claims of the present invention is not exceeded, all should be within the protection scope of the present invention.

Claims (10)

1. The mass and rigidity decoupling ring type MEMS resonator structure is characterized by comprising an anchor point, a resonance ring and a supporting beam positioned between the anchor point and the resonance ring, wherein raised mass blocks are uniformly distributed in the circumferential direction of the resonance ring.

2. The mass stiffness decoupled ring MEMS resonator structure of claim 1, wherein the number of masses is a multiple of 8.

3. The mass-stiffness decoupled ring MEMS resonator structure of claim 1, wherein the mass is any structure with mass.

4. The mass stiffness decoupled ring MEMS resonator structure of claim 1, wherein the mass is uniformly distributed in a circumferential direction of the resonating ring to satisfy a rotational symmetry condition.

5. The method for trimming a mass stiffness decoupled ring MEMS resonator structure according to any of claims 1-4, characterized by the steps of:

s1, frequency cracking is determined through frequency sweep test, and the position of a low-frequency rigid shaft is judged;

s2, selecting the mass block closest to the rigid shaft to adjust, and monitoring whether the rigid shaft is aligned in real time;

and S3, after the rigid shaft is aligned, trimming the two mass blocks aligned with the rigid shaft in equal quantity at the same time until the frequency difference reaches the set requirement.

6. The trimming method according to claim 5, wherein the step S1 is specifically realized by the following method:

the signal input/output end of the phase-locked amplifier is connected with the signal output/input end of the gyro, the harmonic oscillator is excited by a power supply to measure the phase and amplitude of the signal at the driving electrode end of the gyro,

if two peak values exist in the amplitude signal, the rigid shaft has a certain deflection angle, the abscissa corresponding to the peak value is the frequency value of the mode, and the difference between the two abscissas is the frequency cracking value;

if the amplitude signal has only one peak value, the rigid shaft is aligned, the frequency sweeping is continuously carried out by replacing the rigid shaft at the end of the detection electrode, and the frequency difference of the two frequency sweeps is a frequency cracking value.

7. The trimming method according to claim 5, wherein the trimming method in step S2 includes removing mass by femtosecond laser or adding mass by spot-adding conductive adhesive; if the conductive adhesive is added in a point mode, determining the position of the high-frequency rigid shaft through the step S1, and determining the mass block closest to the high-frequency rigid shaft for dispensing; if the mass is removed by the femtosecond laser, the position of the low-frequency rigid axis is determined in step S1, and the mass block closest to the high-frequency rigid axis is determined to be perforated.

8. The trimming method according to claim 5, wherein the trimming simultaneously and equally performed on the two mass blocks with the aligned rigid axes in step S3 comprises point-type addition of conductive adhesive, femtosecond laser mass removal or mass addition; and if the femtosecond laser is adopted for frequency modulation, determining that two mass blocks corresponding to the low-frequency rigid shaft simultaneously punch holes.

9. The trimming method according to claim 5, wherein the trimming further comprises a combination of a removed mass and an added mass, a combination of masses.

10. The trimming method according to claim 5, further comprising a balance trimming comprising the same mass being removed or added at four equivalent symmetric positions simultaneously.

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