CN111624669B

CN111624669B - MEMS quasi-zero-stiffness spring oscillator structure

Info

Publication number: CN111624669B
Application number: CN202010513743.4A
Authority: CN
Inventors: 伍文杰; 涂良成; 刘骅锋; 刘丹丹
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2020-06-08
Filing date: 2020-06-08
Publication date: 2021-10-08
Anticipated expiration: 2040-06-08
Also published as: CN111624669A

Abstract

The invention discloses a MEMS quasi-zero-stiffness spring oscillator structure, which comprises: a plurality of groups of symmetrically arranged spring units, connecting beams and inspection mass; the rigidity of the spring unit is close to zero after the spring unit is subjected to the action of the compressive stress and the tensile stress generated by the gravity of the inspection mass under the action of the gravity; the connecting beam is used for increasing the rigidity of the crossed shaft of the spring vibrator. The prestress is provided by the gravity of the proof mass, and an additional actuator is not needed, so that the structure is simpler. The vibration direction of the spring vibrator is vertical to the prestress direction, and the spring vibrator vibration direction can be used for acceleration horizontal component measurement or horizontal vibration signal isolation. The invention forms a full-symmetrical structural form by connecting a plurality of groups of tensile stress cantilever beams and compressive stress cantilever beams in series and in parallel, has better crossed axis rigidity ratio, and is simpler in modeling, analysis and design.

Description

MEMS quasi-zero-stiffness spring oscillator structure

Technical Field

The invention belongs to the technical field of acceleration measurement, and particularly relates to a fully-symmetrical MEMS quasi-zero-stiffness spring oscillator structure formed by organically combining a plurality of cantilever beams subjected to axial load.

Background

The spring vibrator structure is the most common mechanical structure form in systems such as an acceleration sensor, a shock isolator and the like. For an acceleration sensor, the lower rigidity can amplify the gain of the displacement from an acceleration signal to the proof mass, and the detection of a weak acceleration signal is facilitated; for a vibration isolator, lower stiffness increases the frequency band over which environmental vibrations can be attenuated. Therefore, the quasi-zero stiffness structure is very important for high-precision acceleration sensors and high-performance seismic isolation systems.

In the traditional high-precision acceleration sensor and the shock isolator, a quasi-zero rigidity structure realized by utilizing methods of geometric nonlinearity, positive and negative rigidity offset, structural nonlinearity and the like is widely applied. In recent years, quasi-zero stiffness structures have begun to be used in MEMS acceleration sensors, exhibiting unique advantages in terms of high sensitivity, high stability, and the like. The university of glasgow takes the lead of realizing an MEMS quasi-zero stiffness spring oscillator structure in the vertical direction by utilizing the nonlinear effect of an Euler beam, and applies the MEMS quasi-zero stiffness spring oscillator structure to an MEMS gravimeter to realize the measurement of the earth gravity tide (Middlemis R.et al.Nature 531, 614-617, 2016). Similar work also includes (CN107092038B), (brahim. e.m.et al. microsystems & Nanoengineering, 5(60), 2019), etc. These sensors rely on gravity to apply the pre-stress and cannot be used as horizontal component acceleration measurements.

Patent documents CN110040680A and CN110078014A respectively describe a method for applying a prestress to an euler beam by using thermal and electrostatic forces to realize quasi-zero stiffness, and theoretically, the method can measure acceleration in a horizontal direction and acceleration in a vertical direction; however, the introduction of additional actuators providing prestressing increases the complexity of the system, with problems in terms of cost, power consumption, self-heating, etc.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide an MEMS quasi-zero-stiffness spring oscillator structure, and aims to solve the problems of complex system structure and high power consumption caused by the fact that an actuator for providing prestress is additionally introduced in the prior art.

The invention provides a MEMS quasi-zero-stiffness spring oscillator structure, which comprises: a spring system, a connecting beam and a proof mass; the spring system is subjected to compressive stress and tensile stress generated by the gravity of the inspection mass under the action of gravity, the positive stiffness of the cantilever beam is counteracted by utilizing the negative stiffness effect brought by the axial compressive stress, and the stiffness of the stressed cantilever beam is adjusted to be close to zero; the connecting beam is used for increasing the rigidity of the crossed shaft of the spring vibrator.

Wherein the spring system comprises a plurality of groups of symmetrically arranged spring units.

In particular, the spring system may consist of four or more sets of spring units connected in parallel.

Further, each set of spring elements is composed of one or more pairs of cantilever beams in series, which are respectively under compressive and tensile stress.

Further preferably, each set of spring units comprises: the stressed stress cantilever beam and the stressed stress cantilever beam which are connected in series form a full-symmetrical structural form by combining the stressed stress cantilever beam and the stressed stress cantilever beam, so that the high cross shaft rigidity ratio is realized.

In the embodiment of the invention, the spring stiffness or the eigenfrequency of the spring oscillator structure can be close to zero by reasonably designing the geometric parameters of the spring oscillator structure.

More preferably, the mass of the vibrator is 1ng to 100g, and the cantilever length is 100nm to 100 μm.

Wherein, the width of the cantilever beam can be adjusted within the range of 1 nm-1 mm according to the selected mass of the vibrator and the length of the cantilever beam to realize quasi-zero rigidity.

In an embodiment of the present invention, the spring oscillator structure further includes: and the outer frame is used for fixing the spring oscillator structure on the mounting base.

Compared with the prior art, the invention has the following advantages:

(1) the prestress is provided by the gravity of the proof mass, and an additional actuator is not needed, so that the structure is simpler.

(2) The invention forms a full-symmetrical structural form by connecting a plurality of groups of tensile stress cantilever beams and compressive stress cantilever beams in series and in parallel, has better crossed axis rigidity ratio, and is simpler in modeling, analysis and design.

(3) The vibration direction of the spring vibrator is vertical to the prestress direction, and the spring vibrator vibration direction can be used for acceleration horizontal component measurement or horizontal vibration signal isolation.

Drawings

Fig. 1 is a schematic structural diagram of a MEMS quasi-zero stiffness spring oscillator provided in an embodiment of the present invention.

Fig. 2 is a schematic diagram illustrating deformation of a cantilever beam under axial stress according to an embodiment of the present invention.

Fig. 3 is a physical model diagram of a MEMS quasi-zero stiffness spring oscillator structure provided by an embodiment of the present invention.

Fig. 4 is an example of a quasi-zero stiffness spring oscillator structure of an MEMS based on a similar principle according to an embodiment of the present invention, where (a) is an example where the number of cantilever beams in a spring unit is unchanged and the structural form of the cantilever beams is changed; (b) an example of the variation in the number of cantilever beams in a spring unit.

The reference numerals have the following meanings: 1 is a compression stress cantilever beam, 2 is a tension stress cantilever beam, 3 is a connecting beam, 4 is a detection mass, and 5 is an outer frame.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The invention provides an MEMS quasi-zero stiffness spring oscillator structure which can be used for acceleration horizontal component measurement or horizontal vibration signal isolation; the structure is a fully-symmetrical structure formed by connecting a plurality of groups of tensile stress cantilever beams and compressive stress cantilever beams in series and in parallel, the earth gravity is used for providing prestress, the compressive stress cantilever beams are used for reducing the rigidity of the cantilever beams, and the combination of the compressive stress cantilever beams and the tensile stress cantilever beams is used for realizing high cross shaft rigidity ratio. The structure is prepared by adopting a deep silicon etching process and can be compatible with an MEMS (micro-electromechanical system) process.

The invention can offset the positive stiffness and the negative stiffness of the cantilever beam under the pressure stress by adjusting the width of the cantilever beam to realize the adjustment of the positive stiffness of the cantilever beam or the adjustment of the mass of the oscillator or adjusting the positive stiffness and the negative stiffness of the cantilever beam simultaneously by adjusting the length of the cantilever beam, thereby enabling the spring stiffness or the eigenfrequency of the spring oscillator structure to be close to zero. As an embodiment of the present invention, a single crystal silicon with a thickness of 500 μm may be selected and the structure is prepared by a deep silicon through etching process.

FIG. 1 shows a MEMS quasi-zero stiffness spring oscillator structure; the structure comprises a spring module (consisting of a compressive stress cantilever beam 1 and a tensile stress cantilever beam 2), a connecting beam 3, a check mass 4 and an outer frame 5; the spring module comprises four groups of springs or a plurality of groups of springs which are symmetrically arranged, and two cantilever beams in each group of springs are respectively under the action of pressure stress and tensile stress generated by the gravity of the inspection mass under the action of gravity. The connecting beams 3 serve to increase the cross-axis stiffness of the structure. The outer frame 5 is used to fix the structure to the mounting base.

As an embodiment of the invention, the designed value of the cantilever beam length is 10 mm; the design value of the width of the connecting beam is 100 mu m; the design values of the length and width of the proof mass are 20mm and 14mm respectively. According to the parameters, the width of the cantilever beam corresponding to the structure in the quasi-zero stiffness state can be calculated or simulated to be 15 μm.

FIG. 2 illustrates the structure of an axially stressed cantilever beam; taking the cantilever beam stressed by axial compressive stress as an example, the tail end of the cantilever beam displaces under the action of transverse external force. The moment generated by the axial force now causes this displacement to increase in one part. Therefore, the effect of the axial compressive stress on the cantilever beam can be equivalent to that the cantilever beam is connected in series with a rigidity K_aA negative rate spring. Cantilever beam stiffness (K) under compressive stress_c) Can be written as: k_c≈K_b-K_a… … (1); in the formula, K_bThe stiffness of the cantilever beam is the stiffness without the prestress action. When the pre-stress is a tensile stress, the effect can be equivalent to connecting a positive stiffness spring in series. Cantilever beam stiffness (K) in tensile stress_t) Can be written as: k_t≈K_b+K_a……(2)。

FIG. 3 shows a physical model of a MEMS quasi-zero-stiffness spring oscillator structure provided by an embodiment of the invention; the total stiffness of the spring module can be derived according to the series-parallel connection relation of the springs as follows:

when the width of the cantilever beam is 15 μm, the cantilever beam under the compressive stress is in a quasi-zero stiffness state, and the total stiffness of the system is as follows: k_s≈4×K_c0 … … (4); i.e. the entire spring module is in a quasi-zero stiffness state. According to the actual measurement result, the rigidity of the structure is 5.8 mN/m.

Based on the principle of positive and negative stiffness counteraction and the basic idea of multi-cantilever beam combination, the structural form and the number of the cantilever beams can be changed, as shown in fig. 4, wherein as shown in the figure (a), the number of the cantilever beams is unchanged, each spring unit is still formed by connecting a pair of cantilever beams under the action of compressive stress and tensile stress in series, but the structural form of the spring system is changed. As shown in figure (b), the number of cantilevers varies, and each spring unit is formed by connecting two pairs of cantilever beams in series, which are respectively subjected to compressive stress and tensile stress. .

It is to be noted that the above description and the accompanying drawings are only one of the preferred embodiments of the present invention, and are not intended to limit the present invention. It will be understood by those skilled in the art that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A MEMS quasi-zero stiffness spring oscillator structure, comprising: a spring system, a connecting beam (3) and a proof mass (4);

the spring system comprises a plurality of groups of symmetrically arranged spring units which are connected in parallel, and each group of spring units is formed by connecting one or more pairs of cantilever beams which are respectively stressed by pressure stress and tensile stress in series; the spring system is subjected to compressive stress and tensile stress generated by the gravity of the inspection mass (4) under the action of gravity, the positive stiffness of the cantilever beam is counteracted by utilizing the negative stiffness effect brought by the axial compressive stress, and the stiffness of the stressed cantilever beam is adjusted to be close to zero;

the connecting beam (3) is used for increasing the rigidity of a crossed shaft of the spring vibrator.

2. The spring oscillator structure of claim 1 wherein the spring system is comprised of four sets of spring units connected in parallel.

3. The spring oscillator structure of claim 1 or 2 wherein each group of spring units comprises: the compressive stress cantilever beam (1) and the tensile stress cantilever beam (2) which are connected in series form a full-symmetrical structural form by combining the compressive stress cantilever beam and the tensile stress cantilever beam, so that the high cross-axis rigidity ratio is realized.

4. The spring oscillator structure of claim 3 wherein the spring rate or eigenfrequency of the spring oscillator structure is close to zero by appropriate design of the geometric parameters of the spring oscillator structure.

5. The spring oscillator structure of claim 4 wherein the oscillator has a mass of 1ng to 100g and a cantilever length of 100nm to 100 μm.

6. The spring oscillator structure of claim 5 wherein the width of the cantilever beam is adjustable to achieve quasi-zero stiffness in the range of 1nm to 1mm depending on the oscillator mass and cantilever length selected.

7. The spring oscillator structure of claim 1 wherein the spring oscillator structure further comprises: the outer frame (5), outer frame (5) are used for being fixed in the spring oscillator structure on the mounting base.