CN220795494U - Symmetrical MEMS gravity meter - Google Patents

Abstract

The utility model discloses a symmetrical MEMS gravity meter, which comprises a central mass block, an outer frame, a group of positive rigidity buckling beams and a group of negative rigidity buckling beams. One end of the buckling beam is connected with the central mass block, the other end of the buckling beam is connected with the outer frame, the outer frame provides fixed support for the buckling beam, the central mass block is subjected to external acceleration to generate displacement relative to the outer frame, and the outer frame can limit the displacement range of the central mass block. The two groups of buckling beams adopt a positive and negative rigidity compensation principle, so that the symmetrical MEMS gravimeter has quasi-zero rigidity characteristics and extremely low resonant frequency. The symmetrical MEMS gravimeter has the advantages of small volume, low cost and the like.

Description

A symmetrical MEMS gravimeter

Technical Field

The utility model relates to the field of gravimeters, in particular to a symmetrical MEMS gravimeter.

Background technique

Ever since Newton discovered universal gravitation, humans have been fascinated by the mystery of gravity. Through long-term astronomical observations, scientists have discovered that the movement of celestial bodies in the universe follows the law of universal gravitation. Later, Cavendish conducted a pioneering torsion balance experiment and measured the value of the universal gravitational constant G, which differed from the results measured by modern instruments by less than 1%. Micro-g-Solutions developed the FG5-X absolute gravimeter based on the JILA gravimeter, which became the most advanced and automated gravimeter in the world at that time. Brahim El Mansouri and others from Delft University of Technology developed a high-resolution MEMS inertial sensor with integrated capacitance readings. The resonant frequency of the sensor changes with the tilt angle. When the angle with the horizontal plane is 34°, the resonant frequency of the sensor is observed to be 8.7Hz. According to the noise of the displacement detection circuit and the mechanical sensitivity of the MEMS sensor, its noise power spectrum density is 17ng/√Hz. At present, the CG-5 automatic relative gravimeter designed by the United States using "Fused Silica" technology is widely used as a commercial gravimeter. It has user-friendly operation, no need to reset readings, a resolution of 0.001mGal, a noise power spectrum density of 2μGal/√Hz@1Hz, and a range of 8000mGal. Qu Ziqiang and others from Huazhong University of Science and Technology designed a suspended MEMS gravimeter, and obtained the noise power spectrum density of the MEMS gravimeter to be 2.4ng/√Hz@10Hz through a fiber optic displacement sensor. In addition, R.P.Middlemiss and others from the University of Glasgow designed a MEMS gravimeter with a three-cantilever beam structure. This asymmetric "geometrical anti-spring" design makes the MEMS gravimeter have an extremely low resonant frequency. According to reports, its noise power spectrum density is 40μGal/√Hz@1Hz, and the drift reaches 111μGal/day.

The research on gravimeters gradually matured at the end of the last century, such as FG5-X, CG-5, etc. The FG5-X gravimeter developed by Micro-g&LaCoste has an accuracy of 15μGal, but its total weight reaches 150Kg and its volume is ^1.5m3 . It is precisely because of the defects of traditional commercial gravimeters such as large volume, high cost and non-popularity that the difficulty and research cost of gravity detection are increased. This paper miniaturizes the traditional large-volume gravimeter by combining MEMS technology, reducing the production cost of the gravimeter.

In order to make the MEMS gravimeter more sensitive to slight changes in gravitational acceleration, according to the formula: Δa = Δx·(2πf ₀ ² )

Where Δa is the change in acceleration, Δx is the displacement of the central mass block, and _f0 is the resonant frequency of the MEMS gravimeter. When the MEMS gravimeter has an extremely low resonant frequency, a slight change in gravity acceleration will cause a large displacement of the central mass block. This design is beneficial for subsequent displacement detection. According to the formula:

Where k is the stiffness of the MEMS gravimeter, and m is the mass of the MEMS gravimeter. Traditional commercial gravimeters can reduce the resonant frequency by increasing the mass of the sensor, but the characteristic of MEMS technology is to miniaturize the gravimeter, so the volume and mass of the MEMS gravimeter are much smaller than those of the commercial superconducting gravimeter GWR-iGrv, atomic interferometer gravimeter Micro-g FG-515, etc. How to design a gravimeter with extremely low stiffness and resonant frequency is a problem currently under development.

Utility Model Content

The utility model aims to provide a symmetrical MEMS gravimeter, which has the advantages of reduced volume, mass and manufacturing cost.

The above technical objectives of the utility model are achieved through the following technical solutions:

A symmetrical MEMS gravimeter comprises a central mass block, an outer frame and two groups of buckling beams, wherein the two groups of buckling beams are respectively a group of positive stiffness buckling beams and a group of negative stiffness buckling beams.

The outer frame provides fixed support for the buckling beam, and an outer frame limiting space is provided inside the outer frame, and the outer frame limiting space is used to limit the displacement range of the central mass block;

The central mass block is located in a limited space of the outer frame, and the central mass block is displaced relative to the outer frame under the action of external forces;

The two groups of buckling beams are connected to the central mass block at one end and to the outer frame that can provide fixed support at the other end.

Preferably, the positive stiffness buckling beam and the negative stiffness buckling beam are connected in parallel to perform stiffness compensation.

Preferably, the positive stiffness buckling beam comprises a first positive stiffness buckling beam and a second positive stiffness buckling beam, and the negative stiffness buckling beam comprises a first negative stiffness buckling beam and a second negative stiffness buckling beam, the first positive stiffness buckling beam and the second positive stiffness buckling beam are left-right symmetrical about the central mass block, and the first negative stiffness buckling beam and the second negative stiffness buckling beam are also left-right symmetrical about the central mass block.

Preferably, four central support structures are provided on the central mass block, the four central support structures are central support structure 1, central support structure 2, central support structure 3 and central support structure 4, central support structure 1 and central support structure 2 are symmetrical about the central mass block, and central support structure 3 and central support structure 4 are symmetrical about the central mass block;

Four frame support structures are provided on the inner side surface of the outer frame, and the four frame support structures are frame support structure 1, frame support structure 2, frame support structure 3 and frame support structure 4;

The two ends of the first positive stiffness buckling beam are respectively connected to the central support structure one and the frame support structure one; the two ends of the second positive stiffness buckling beam are respectively connected to the central support structure two and the frame support structure two; the two ends of the first negative stiffness buckling beam are respectively connected to the central support structure three and the frame support structure three, and the two ends of the second negative stiffness buckling beam are respectively connected to the central support structure four and the frame support structure four.

Preferably, when the central mass block is displaced relative to the outer frame under the action of gravity, causing the group of negative stiffness buckling beams to exhibit negative stiffness characteristics, the group of positive stiffness buckling beams are still positive stiffness, and the positive stiffness buckling beams and the negative stiffness buckling beams are connected in parallel to compensate for stiffness, so that the symmetrical MEMS gravimeter has a quasi-zero stiffness characteristic, thereby effectively reducing the resonant frequency of the symmetrical MEMS gravimeter.

The beneficial effects of the utility model are:

(1) Under the action of gravity, the resonant frequency of the symmetrical MEMS gravimeter can reach 10 Hz or even lower, which means that the MEMS gravimeter is extremely sensitive to slight changes in acceleration;

(2) The design of the buckled beam ensures that the symmetrical MEMS gravimeter will not lose the quasi-zero stiffness characteristic due to the change of beam width caused by MEMS process errors, thereby reducing the impact of process processing;

(3) The microstructure size of the symmetrical MEMS gravimeter can be controlled within 20 mm × 20 mm × 0.2 mm, making it smaller in volume and mass than traditional gravimeters;

(4) Thanks to the mass production capability of MEMS technology, the symmetrical MEMS gravimeter can be mass-produced, effectively reducing the production cost of the MEMS gravimeter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the overall structure of a symmetrical MEMS gravimeter provided by an embodiment of the utility model;

FIG2 is a partial view of the top of the central mass block provided in an embodiment of the present utility model;

FIG3 is a force-displacement curve of a symmetrical MEMS gravimeter provided in an embodiment of the utility model;

FIG4 is a curve showing the resonant frequency of the symmetrical MEMS gravimeter provided in an embodiment of the present utility model and the angle between the MEMS gravimeter and the horizontal plane;

FIG. 5 a , FIG. 5 b and FIG. 5 c are force-displacement curves of a symmetrical MEMS gravimeter based on buckling beams of different widths provided in an embodiment of the present invention.

In all the drawings, "d" indicates a depth direction, "w" indicates a width direction, and "l" indicates a length direction, that is, a horizontal direction.

Figure markings: 1. Central mass block; 2. Outer frame; 3. Buckling beam; 3a. Positive stiffness buckling beam; 3a-1. First positive stiffness buckling beam; 3a-2. Second positive stiffness buckling beam; 3b. Negative stiffness buckling beam; 3b-1. First negative stiffness buckling beam; 3b-2. Second negative stiffness buckling beam; 4. Central support structure; 4a. Central support structure one; 4b. Central support structure two; 4c. Central support structure three; 4d. Central support structure four; 5. Frame support structure; 5a. Frame support structure one; 5b. Frame support structure two; 5c. Frame support structure three; 5d. Frame support structure four; 6. Outer frame defines space.

Detailed ways

In order to make the purpose, technical solution and advantages of the utility model clearer, the utility model 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 utility model and are not used to limit the utility model. In addition, the technical features involved in each embodiment of the utility model described below can be combined with each other as long as they do not conflict with each other.

As shown in FIG1 , in an embodiment of the utility model, a symmetrical MEMS gravimeter is disclosed, which includes: a central mass block 1, an outer frame 2, a group of positive stiffness buckling beams 3a and a group of negative stiffness buckling beams 3b. The buckling beams 3 are connected to the central mass block 1 at one end and to the outer frame 2 that can provide fixed support at the other end, and are symmetrical about the central mass block 1. The central mass block 1 is located in a limited space 6 of the outer frame 2, and is displaced relative to the outer frame 2 by external acceleration. The outer frame 2 provides fixed support for the buckling beams 3 and limits the displacement range of the central mass block 1.

As shown in FIG. 1 and FIG. 2, in the implementation of the utility model, a symmetrical MEMS gravimeter is disclosed, and the two ends of the central mass block 1 have four central support structures 4, and the four central support structures 4 are respectively a central support structure 1 4a, a central support structure 2 4b, a central support structure 3 4c and a central support structure 4 4d, and the inner side of the outer frame 2 has four frame support structures 5, and the four frame support structures 5 are respectively a frame support structure 1 5a, a frame support structure 2 5b, a frame support structure 3 5c and a frame support structure 4 5d, and the positive stiffness The buckling beam 3a is symmetrical about the central mass block 1, the negative stiffness buckling beam 3b is symmetrical about the central mass block 1, the two ends of the positive stiffness buckling beam 3a-1 are connected to the support structures 4a and 5a, the two ends of the positive stiffness buckling beam 3a-2 are connected to the support structures 4b and 5b, the two ends of the negative stiffness buckling beam 3b-1 are connected to the support structures 4c and 5c, and the two ends of the negative stiffness buckling beam 3b-2 are connected to the support structures 4d and 5d. This design reduces the stress at the root of the buckling beam 3 and improves the stability of the connection with the outer frame 2 and the central mass block 1. Figure 2 shows more clearly the relative size of the central mass block 1 and the positive stiffness buckling beam 3a in the embodiment. "Depth direction" is represented by "d", "width direction" is represented by "w", and "length direction" is represented by "l". In FIGS. 1 and 2 , the width of the positive stiffness buckling beam 3 a is represented by “w _flex ”, the thickness is represented by “d _flex ”, the width of the central mass block 1 is represented by “w _mass ”, the thickness is represented by “d _mass ”, and the length is represented by “l _mass ”.

As shown in FIG3 , the embodiment of the utility model provides a force-displacement relationship curve of a symmetrical MEMS gravimeter; the dotted line in the figure represents the force-displacement relationship curve of the negative stiffness buckling beam 3b, the dashed line in the figure represents the force-displacement relationship curve of the positive stiffness buckling beam 3a, and the solid line in the figure represents the force-displacement relationship curve of the symmetrical MEMS gravimeter. In the force-displacement relationship curve, the positive stiffness buckling beam 3a and the negative stiffness buckling beam 3b in the region I both show positive stiffness, the positive stiffness buckling beam 3a in the region II shows positive stiffness, and the negative stiffness buckling beam 3b shows negative stiffness. By performing stiffness compensation on the positive stiffness buckling beam 3a and the negative stiffness buckling beam 3b, the symmetrical MEMS gravimeter has extremely low stiffness, and the stiffness is a fixed value. This design scheme can effectively reduce the stiffness and resonant frequency of the symmetrical MEMS gravimeter, and the positive stiffness buckling beam 3a and the negative stiffness buckling beam 3b in the region III both show positive stiffness.

As shown in Figure 4, the embodiment of the utility model provides a resonant frequency-angle curve of the MEMS gravimeter with the horizontal plane of the symmetrical MEMS gravimeter. When the angle range of the symmetrical MEMS gravimeter with the horizontal plane is 0° to 90°, the resonant frequency decreases with the increase of the angle. When the angle range of the symmetrical MEMS gravimeter with the horizontal plane is 90° to 92°, the resonant frequency increases with the increase of the angle. When the angle range of the symmetrical MEMS gravimeter with the horizontal plane is 88° to 92°, the resonant frequency of the symmetrical MEMS gravimeter does not exceed 10Hz. When the angle with the horizontal plane is 90°, the resonant frequency is 8.9Hz. The mass of the central mass block 1 does not exceed 80mg.

As shown in FIG. 5 , the embodiment of the present invention provides force-displacement curves of symmetrical MEMS gravimeters with buckling beams of different widths. The deep reactive ion etching (DRIE) technology will affect the width “w _flex” of the buckling beam 3. 5a-5c respectively show the force-displacement curves of the symmetrical MEMS gravimeters with the width of the buckled beam 3 of 18μm, 16μm and 12μm. The symmetrical MEMS gravimeters with three different beam widths still have the quasi-zero stiffness characteristic, but the buckling load decreases with the decrease of the beam width, which means that the symmetrical MEMS gravimeter is fixed at a suitable angle, that is, when the gravity component in the direction of the sensitive axis is equal to the buckling load, the MEMS gravimeter can have the quasi-zero stiffness characteristic and extremely low resonant frequency. When the width of the buckled beam 3 is 18μm, the resonant frequency of the symmetrical MEMS gravimeter is 6.87Hz, when the width of the buckled beam 3 is 16μm, the resonant frequency of the symmetrical MEMS gravimeter is 8.44Hz, and when the width of the buckled beam 3 is 12μm, the resonant frequency of the symmetrical MEMS gravimeter is 5.16Hz.

It is easy for those skilled in the art to understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (4)

1. A symmetrical MEMS gravimeter, comprising a central mass block, an outer frame and two groups of buckling beams, wherein the two groups of buckling beams are respectively a group of positive stiffness buckling beams and a group of negative stiffness buckling beams, characterized in that: The outer frame provides fixed support for the buckling beam, and an outer frame limiting space is provided inside the outer frame, and the outer frame limiting space is used to limit the displacement range of the central mass block; The central mass block is located in a limited space of the outer frame, and the central mass block is displaced relative to the outer frame under the action of external forces; The two groups of buckling beams are connected to the central mass block at one end and to the outer frame that can provide fixed support at the other end. 2. A symmetrical MEMS gravimeter according to claim 1, characterized in that the positive stiffness buckling beam and the negative stiffness buckling beam are connected in parallel to perform stiffness compensation. 3. A symmetrical MEMS gravimeter according to claim 1, characterized in that the positive stiffness buckling beam includes a first positive stiffness buckling beam and a second positive stiffness buckling beam, the negative stiffness buckling beam includes a first negative stiffness buckling beam and a second negative stiffness buckling beam, the first positive stiffness buckling beam and the second positive stiffness buckling beam are left-right symmetrical about the central mass block, and the first negative stiffness buckling beam and the second negative stiffness buckling beam are also left-right symmetrical about the central mass block. 4. A symmetrical MEMS gravimeter according to claim 1, characterized in that four central support structures are provided on the central mass block, the four central support structures are central support structure 1, central support structure 2, central support structure 3 and central support structure 4, central support structure 1 and central support structure 2 are symmetrical about the central mass block, and central support structure 3 and central support structure 4 are symmetrical about the central mass block; Four frame support structures are provided on the inner side surface of the outer frame, and the four frame support structures are frame support structure 1, frame support structure 2, frame support structure 3 and frame support structure 4; The two ends of the first positive stiffness buckling beam are respectively connected to the central support structure one and the frame support structure one; the two ends of the second positive stiffness buckling beam are respectively connected to the central support structure two and the frame support structure two; the two ends of the first negative stiffness buckling beam are respectively connected to the central support structure three and the frame support structure three, and the two ends of the second negative stiffness buckling beam are respectively connected to the central support structure four and the frame support structure four.