Frequency matched microhemispherical resonator and manufacturing method

Abstract

This invention discloses a frequency-matched micro-hemispherical resonator and its manufacturing method. The frequency-matched micro-hemispherical resonator includes a micro-shell structure and a stiffness amplification structure. The micro-shell structure includes a shell and a hollow support column disposed within the shell. The bottom of the hollow support column is flat. The stiffness amplification structure is disposed on the outside of the shell. The stiffness amplification structure is used to increase the equivalent mass and equivalent stiffness of the micro-shell structure in any direction. The micro-shell structure and the stiffness amplification structure are integrally fabricated using fused silica material. This invention adds a stiffness amplification structure to the micro-shell structure, which can simultaneously increase the equivalent mass and equivalent stiffness on the mode axis in any direction. Therefore, even if there are manufacturing errors in the micro-shell structure, the stiffness amplification structure can still adjust the natural frequency to achieve frequency matching.

Description

Technical Field

[0001] This invention relates to the field of gyroscope resonator technology, and more specifically, to a frequency-matched micro-hemispherical resonator and its manufacturing method. Background Technology

[0002] Currently, the mainstream fabrication method for micro-hemispherical gyroscope resonators involves first softening a fused silica sheet using a high-temperature torch, then releasing the resonator from the fused silica sheet using methods such as laser, etching, and chemical mechanical polishing. Based on this method, the University of Michigan and the National University of Defense Technology have successively fabricated resonators with different shapes and structures, including microshell, bell-shaped, Birdbath-shaped, variable-thickness PSI-shaped, and micro-hemispherical resonators. The University of Michigan typically uses chemical mechanical polishing for structural release, while the National University of Defense Technology uses femtosecond laser ablation to process T-shaped and toothed mass blocks at the edges of the micro-hemispherical resonator, increasing the gyroscope's driving and detection efficiency. After releasing the micro-hemispherical resonator, subsequent processes such as coating and assembly are performed to form the gyroscope head.

[0003] Based on existing designs from the University of Michigan and the National University of Defense Technology, micro-hemispherical resonators typically exhibit frequency fragmentation on the order of 10 Hz. Micro-hemispherical resonators used in gyroscopes often require material removal processes such as laser ablation and ion beam etching to maintain structural balance and reduce frequency fragmentation. Generally, rate-mode gyroscopes require frequency fragmentation on the order of 0.1 Hz, while full-angle-mode gyroscopes have even higher requirements. Therefore, mechanical tuning of the micro-hemispherical resonator is crucial.

[0004] The principle of mechanical adjustment using methods such as laser ablation, ion beam etching, and chemical etching is to adjust the two inherent modes of the resonator. By removing or adding material, the inherent frequencies of the two modes are brought closer together, thus reducing frequency fragmentation. This post-processing method has several drawbacks: 1. Low efficiency. Because each resonator has different processing errors, modal testing is required for each resonator individually to determine process parameters, often requiring multiple iterations in the adjustment process. Each sample needs a separate adjustment process, which restricts the mass production of micro-hemispherical resonant gyroscopes; 2. Structural damage. Mechanical adjustment requires the removal of some material, resulting in an incomplete structure and potentially introducing new performance damage, such as deteriorated surface quality, reduced quality factor, and burns to the electrode gold film. Therefore, it is indeed necessary to provide a frequency-matched micro-hemispherical resonator and its manufacturing method. Summary of the Invention

[0005] The purpose of this invention is to provide a frequency-matched micro-hemispherical resonator and its manufacturing method to overcome the defects of the prior art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A frequency-matched micro-hemispherical resonator includes a micro-shell structure and a stiffness amplification structure. The micro-shell structure includes a shell and a hollow support column disposed within the shell. The bottom of the hollow support column is a plane. The stiffness amplification structure has the same equivalent mass and equivalent stiffness. The micro-shell structure and the stiffness amplification structure are integrally fabricated using fused silica material.

[0008] Furthermore, the micro-shell structure is a rotationally symmetric curved shell structure, and the stiffness amplification structure is a planar ring, which is integrally disposed on the outside of the shell.

[0009] Furthermore, the surface of the curved shell structure is an arbitrary shape surface.

[0010] Furthermore, the stiffness amplification structure is a planar circular ring or a regular N-gon structure, where N is 8 or a multiple of 8.

[0011] The present invention also provides a method for fabricating the frequency-matched micro-hemispherical resonator according to the above, comprising the following steps:

[0012] S1. Blowing: A double-sided polished molten quartz sheet is placed on the upper surface of a graphite mold. The molten quartz sheet is softened by heating and enters the graphite mold cavity to form a micro-shell structure.

[0013] S2, Release, including pre-release, modal testing, and batch release. The pre-release includes: taking out a set number of samples blown in step S1 and fixing them onto a circular fixture; placing the circular fixture on a femtosecond laser processing stage for software positioning; and releasing each sample to produce a stiffness amplification structure of different sizes. The modal testing includes performing modal tests on the pre-released samples to obtain batch release processing parameters. The batch release includes using the batch release processing parameters to batch release all the samples blown in step S1.

[0014] S3. Clean and anneal the frequency-matched micro-hemispherical resonators after batch release.

[0015] Furthermore, in step S1, the graphite mold cavity is connected to a vacuum control system through air holes, and the vacuum control system is used to maintain a constant negative pressure inside the graphite mold cavity.

[0016] Furthermore, in step S1, a flame of propane and oxygen combustion is used to heat the surface of the molten quartz sheet using a high-temperature torch, and the temperature of the molten quartz sheet surface is adjusted by controlling the flow rate of propane and oxygen.

[0017] Furthermore, in step S1, the graphite mold is fixed on a high-speed rotating platform, and both the graphite mold and the molten quartz sheet are in a high-speed rotating state during the heating of the molten quartz sheet surface.

[0018] Furthermore, in the modal test of step S2, if frequency matching exists, the stiffness of the sample is enlarged and the structural dimensions are determined as the batch release processing parameters; if no sample with frequency matching exists, the pre-release and modal test steps are repeated.

[0019] Furthermore, in the repeated pre-release step, the size of the stiffness amplification structure is changed to be different from the size of the stiffness amplification structure used in the previous pre-release. When the outer diameter of the stiffness amplification structure of the previous pre-release sample is larger and the frequency fragmentation is greater, the size of the stiffness amplification structure of the current pre-release is reduced; when the outer diameter of the stiffness amplification structure of the previous pre-release sample is larger and the frequency fragmentation is smaller, the size of the stiffness amplification structure of the current pre-release is increased.

[0020] Compared with the prior art, the advantages of the present invention are as follows: The present invention adds a stiffness amplification structure to the micro-shell structure, which can simultaneously increase the equivalent mass and equivalent stiffness on the mode axis in any direction. Therefore, even if there are manufacturing errors in the micro-shell structure, the stiffness amplification structure can still control the natural frequency to achieve frequency matching. The present invention finds the stiffness amplification structure size of the frequency matching micro-hemispherical resonator through one or more pre-release and modal tests. The stiffness amplification structure size is determined as the batch release processing parameter, so that the frequency matching micro-hemispherical resonator can be mass-produced. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 Image a is a schematic diagram of the frequency-matched micro-hemispherical resonator of the present invention, and image b is a cross-sectional view of the structure.

[0023] Figure 2 This is a schematic diagram of the batch release process in this invention. Detailed Implementation

[0024] The preferred embodiments of the present invention will now be described in detail 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, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0025] See Figure 1and Figure 2 As shown, this embodiment discloses a frequency-matched micro-hemispherical resonator, including a micro-shell structure 1 and a stiffness amplification structure 2. The micro-shell structure includes a shell and a hollow support column 3 disposed within the shell. The bottom of the hollow support column 3 is flat and can be used for anchoring. The stiffness amplification structure is disposed on the outside of the shell. The stiffness amplification structure is used to increase the equivalent mass and equivalent stiffness of the micro-shell structure in any direction. The micro-shell structure and the stiffness amplification structure are integrally fabricated using fused silica material.

[0026] In this embodiment, the microshell structure 1 is a rotationally symmetric curved shell structure (i.e., a curved thin-walled portion), and the stiffness amplification structure 2 is a planar ring. This planar ring is integrally disposed on the outside of the shell, increasing the equivalent mass and equivalent stiffness of the microshell structure. Furthermore, it increases the same equivalent mass and equivalent stiffness in any mode axis direction. Even if there are manufacturing errors in the microshell structure, the two natural frequencies of the resonator can be adjusted by increasing this part of the equivalent mass and equivalent stiffness to achieve frequency matching.

[0027] For example, when the fused silica sheet is 250µm thick and the blown microshell structure has a diameter of 11.7mm, the thin-walled portion of the curved surface of the microshell structure exhibits a fourth harmonic. If the existing release method is used, releasing a toothed mass block at the edge of the microshell structure, frequency fragmentation occurs, and the magnitude of the frequency fragmentation is directly proportional to the magnitude of the fourth harmonic of the wall thickness; a 1µm fourth harmonic will cause a 15Hz frequency fragmentation. If a 13.1mm diameter stiffness amplification structure is released at the edge of the microshell structure, then frequency fragmentation is almost nonexistent regardless of the magnitude of the fourth harmonic. That is, the stiffness amplification structure modulates the resonator's natural frequency, achieving frequency matching.

[0028] Preferably, the surface of the curved shell structure is an arbitrary shape.

[0029] Preferably, the stiffness amplification structure is a regular polygonal structure, which can be a regular octagon, a regular hexagon, etc., as long as the same equivalent mass and equivalent stiffness can be added in all directions.

[0030] The present invention also provides a method for fabricating the frequency-matched micro-hemispherical resonator according to the above, comprising the following steps:

[0031] Step S1: Blowing. Place the double-sided polished molten quartz sheet on the upper surface of the graphite mold. Soften the molten quartz sheet by heating and allow it to enter the graphite mold cavity to form a micro-shell structure.

[0032] The graphite mold cavity is connected to a vacuum control system through air holes. The vacuum control system is used to maintain a constant negative pressure inside the graphite mold cavity.

[0033] In this embodiment, a propane and oxygen combustion flame is used to heat the surface of a molten quartz sheet via a high-temperature blowtorch, and the temperature of the molten quartz sheet surface is regulated by controlling the flow rates of propane and oxygen. As the flame heats the sheet, the temperature rises above its softening temperature. Under the pressure difference between the upper and lower surfaces, the softened molten quartz sheet deforms into the graphite mold cavity, forming a three-dimensional shell structure.

[0034] In this embodiment, a graphite mold is fixed on a high-speed rotating platform. During the heating of the molten quartz sheet surface, both the graphite mold and the molten quartz sheet are in a high-speed rotating state, which can make the temperature on the molten quartz sheet more uniform and improve the symmetry of the resonant structure.

[0035] In this embodiment, to ensure the consistency of the resonant structure dimensions during processing, strict control of the flame temperature and heating time is required. Precise control of the flame temperature is achieved by controlling the pressure and flow rate of propane and oxygen. The gas output from the gas cylinder's pressure reducing valve is at a constant pressure, and a flow meter is used to adjust the flow rate, ensuring stable heating temperature through constant pressure and flow. The heating time is controlled by the Z-axis moving platform. Once the gas flow rate reaches the set value, the PLC rapidly moves the flame torch to the designated height to heat the molten quartz sheet. After heating for the set time, the torch moves upward, reducing the gas flow rate, thus completing the processing.

[0036] In this embodiment, to improve the uniformity of temperature distribution on the fused silica sheet, it is necessary to prioritize ensuring the axial runout of the rotating platform. During processing, the installation position of the graphite mold is adjusted using a roundness gauge to ensure that the mold center coincides with the center of the rotating platform, thereby guaranteeing the symmetry of the temperature distribution on the fused silica sheet during heating. The horizontal displacement platform is used for adjusting the position of the flame center and the rotation axis center, while the Z-axis displacement platform is used for controlling the flame height. Due to the large diameter and length of the flame, and the continuous temperature variation within the flame, the positioning accuracy of the displacement platform (±0.01mm) ensures a uniform temperature distribution.

[0037] Step S2, Release, includes pre-release, modal testing, and batch release.

[0038] The pre-release includes: taking out a set number of samples blown in step S1 and sticking them on the disc fixture 4; placing the disc fixture 4 on the femtosecond laser processing stage for software positioning; and releasing stiffness amplification structures of different sizes for each sample. Specifically, the outer diameter of the stiffness amplification structure of different samples varies in a gradient.

[0039] The modal testing includes: performing modal testing on the pre-released samples to obtain batch release processing parameters, specifically:

[0040] If a sample with frequency matching exists, the stiffness of that sample is enlarged to determine the batch release processing parameters.

[0041] If no frequency-matched sample is available, repeat the pre-release and modal testing. Change the dimensions of the stiffness amplification structure to differ from the size of the stiffness amplification structure used in the previous pre-release. Specifically, if the outer diameter D of the stiffness amplification structure in the previous pre-release sample is larger and the frequency fragmentation is greater, decrease the size of the stiffness amplification structure in this pre-release; conversely, if the outer diameter D of the stiffness amplification structure in the previous pre-release sample is larger and the frequency fragmentation is smaller, increase the size of the stiffness amplification structure in this pre-release.

[0042] Until a frequency-matching sample is found among the pre-release samples, the stiffness enlargement structural dimensions of that sample are determined as the batch release processing parameters.

[0043] The batch release includes batch releasing all the blown samples in step S1 using batch release processing parameters, that is: a large number of blown samples are fixed on the disc fixture 4, the disc fixture 4 is placed on the femtosecond laser processing stage, and software positioning is performed. Each sample is released with the same size stiffness amplification structure using the batch release processing parameters determined in the modal test.

[0044] The release process can be femtosecond laser ablation, nanosecond laser ablation, picosecond laser ablation, wet etching, chemical mechanical polishing, laser-assisted wet etching, etc., as long as it can release the structure according to the designed size.

[0045] Step S3: Clean and anneal the frequency-matched micro-hemispherical resonators after batch release.

[0046] The micro-hemispherical resonator of this invention differs from existing designs. It adds a stiffness amplification structure to the micro-shell structure, which can simultaneously increase the equivalent mass and equivalent stiffness on the mode axis in any direction. Thus, even if there are manufacturing errors in the micro-shell structure, the stiffness amplification structure can still adjust the natural frequency to achieve frequency matching.

[0047] This invention proposes a method for manufacturing a frequency-matched micro-hemispherical resonator. The blowing process in step S1 and the post-processing in step S3 are consistent with methods used in existing literature. The key point lies in step S2, release. Through one or more pre-releases and modal tests, the stiffness amplification structure dimensions of the frequency-matched micro-hemispherical resonator are determined, primarily by the outer diameter of the stiffness amplification structure. This stiffness amplification structure dimension is then used as the batch release processing parameter, enabling the mass production of frequency-matched micro-hemispherical resonators.

[0048] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, the patent owner may make various modifications or alterations within the scope of the appended claims, as long as they do not exceed the protection scope described in the claims of the present invention, they shall be within the protection scope of the present invention.

Claims

1. A method for fabricating a frequency matched microhemispherical resonator, comprising: The frequency-matched micro-hemispherical resonator includes a micro-shell structure and a stiffness amplification structure. The micro-shell structure includes a shell and a hollow support column disposed within the shell. The bottom of the hollow support column is flat. The stiffness amplification structure is disposed on the outside of the shell. The stiffness amplification structure is used to increase the equivalent mass and equivalent stiffness of the micro-shell structure in any direction. The micro-shell structure and the stiffness amplification structure are integrally fabricated using fused silica material. ​ The microshell structure is a rotationally symmetric curved shell structure, and the stiffness amplification structure is a planar ring, which is integrally disposed on the outside of the shell. Alternatively, the stiffness-enhancing structure may be a regular N-gon structure, where N is 8 or a multiple of 8; The method for fabricating the frequency-matched micro-hemispherical resonator includes the following steps: S1. Blowing: Place a double-sided polished fused silica sheet on the upper surface of a graphite mold. Soften the fused silica sheet by heating and allow it to enter the graphite mold cavity to form a frequency-matched micro-hemispherical resonator sample with a micro-shell structure. S2, Release, including pre-release, modal testing, and batch release. The pre-release includes: taking out a set number of samples blown in step S1 and fixing them onto a circular jig; placing the circular jig on a femtosecond laser processing stage for software positioning; and releasing each sample to produce a stiffness amplification structure of different sizes. The modal testing includes performing modal tests on the pre-released samples to obtain batch release processing parameters. The batch release includes using the batch release processing parameters to batch release all the samples blown in step S1. S3. Clean and anneal the frequency-matched micro-hemispherical resonators after batch release.

2. The method of claim 1, wherein the frequency matching micro-hemispherical resonator is formed by the steps of: The curved surface of the curved shell structure can be any shape.

3. The method for fabricating a frequency-matched micro-hemispherical resonator according to claim 1, characterized in that, In step S1, the graphite mold cavity is connected to a vacuum control system through air holes. The vacuum control system is used to maintain a constant negative pressure inside the graphite mold cavity.

4. The method for fabricating a frequency-matched micro-hemispherical resonator according to claim 1, characterized in that, In step S1, a flame of propane and oxygen combustion is used to heat the surface of the molten quartz sheet using a high-temperature torch, and the temperature of the molten quartz sheet surface is adjusted by controlling the flow rate of propane and oxygen.

5. The method for fabricating a frequency-matched micro-hemispherical resonator according to claim 1, characterized in that, In step S1, the graphite mold is fixed on a high-speed rotating platform, and both the graphite mold and the molten quartz sheet are in a high-speed rotating state during the heating of the molten quartz sheet surface.

6. The method for fabricating a frequency-matched micro-hemispherical resonator according to claim 1, characterized in that, If frequency matching exists in the modal test of step S2, the stiffness of the sample is enlarged and the structural dimensions are determined as the batch release processing parameters. If no frequency matching exists, the pre-release and modal test steps are repeated.

7. The method for fabricating a frequency-matched micro-hemispherical resonator according to claim 6, characterized in that, In the repeated pre-release step, the size of the stiffness amplification structure is changed to be different from that of the stiffness amplification structure used in the previous pre-release. If the outer diameter of the stiffness amplification structure of the previous pre-release sample is larger and the frequency fragmentation is greater, the size of the stiffness amplification structure of the current pre-release is reduced; if the outer diameter of the stiffness amplification structure of the previous pre-release sample is larger and the frequency fragmentation is smaller, the size of the stiffness amplification structure of the current pre-release is increased.

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