Quartz pendulum plate based on four flexible beam structure and forming method thereof

Abstract

The present application relates to a quartz pendulum plate based on four flexible beam structures and a forming method thereof, the quartz pendulum plate comprising a pendulum tongue, a support ring and flexible beams flexibly connecting the pendulum tongue to the support ring, the flexible beams being four, the four flexible beams being arranged in parallel, wherein two main flexible beams provide main rigidity and are responsible for supporting the pendulum tongue; the other two auxiliary flexible beams are relatively thin and narrow and are responsible for electrically connecting the support ring and the surface gold film of the pendulum tongue. The present application, on one hand, suppresses the influence of thermal stress caused by the mismatch of the thermal expansion coefficients of the pendulum plate material and the film material through the design of the auxiliary flexible beam structure; on the other hand, the two main flexible beams are no longer affected by the creep of the gold film layer, and the gradual round corner setting of the root of the flexible beam reduces the stress concentration of the sharp corner, thereby solving the problem of micro-yield creep of the flexible beam caused by long-term placement in a fixed posture, and further improving the temperature stability and time stability of the quartz flexible accelerometer.

Description

Technical Field

[0001] This invention belongs to the field of inertial sensor technology, specifically relating to a quartz pendulum based on a four-flexible beam structure and its forming method. Background Technology

[0002] Quartz flexible accelerometers are currently the simplest and most widely used high-precision accelerometers in domestic inertial navigation and guidance systems. With increasing system requirements, accelerometers are demanding extremely high stability over long periods and across the entire temperature range, as well as adaptability to environments such as shock, vibration, high humidity, and high heat.

[0003] The quartz flexible accelerometer employs a technical solution that uses flexible supports to sensitively detect mass, capacitance to detect displacement changes, and a permanent magnet torque generator to generate inertial torque, thus achieving acceleration measurement. The pendulum is the core component inside the accelerometer. Figure 1 This is a schematic diagram of the pendulum structure of a traditional quartz flexible accelerometer. It includes a pendulum tongue 4 (the sensitive sensing mass, the moving part), a support ring 1, and two flexible beams 2 and 3 that flexibly connect the pendulum tongue to the support ring. Three bosses 5, 6, and 7 are axially positioned on the support ring. Conductive gold films 8 and 9 are on the support ring, 10 is on the pendulum tongue, and 11 and 12 are on the flexible beams. The same gold films are symmetrically distributed on the other side of the pendulum (not shown in the diagram). This allows the pendulum tongue to swing along the input sensing axis (perpendicular to the plane of the paper). Generally, the pendulum material is quartz glass with a coefficient of linear expansion of 0.54 × 10⁻⁶. -6 / ℃. Conductive metal films are formed on both sides of the pendulum using vacuum deposition technology in specific areas of the pendulum tongue, thus forming the moving electrode of the parallel plate capacitor. A conductive metal film and necessary conductive pads are formed in specific areas of the support ring. These pads are partially responsible for electrical connections to the leads on the accelerometer via gold wires. Some examples of the flexible beam may include at least one thin-film lead that establishes an electrical connection between the conductive film layer of the support ring and the conductive film layer of the pendulum tongue; this lead is generally a gold film deposited on the surface of the flexible beam using vacuum deposition technology, with gold having a coefficient of linear expansion of 14.2 × 10⁻⁶. -6 / ℃.

[0004] Most existing quartz flexible accelerometer pendulums adopt a double flexible beam symmetrical structure, such as... Figure 1 As shown, it achieves acceleration sensitivity by supporting the pendulum tongue with double beams. Gold films are plated onto the double beams to provide electrical connection between the support ring and the pendulum tongue. However, the following problems exist:

[0005] First, the accelerometer output exhibits temperature hysteresis. During manufacturing and operation, the accelerometer's output becomes unstable or exhibits temperature hysteresis due to temperature effects, and it may even fail to return to zero after the temperature change ends. For the pendulum, one of the main influencing factors of this effect is the unavoidable processing errors in the gold film coating on the flexible beam surface, such as asymmetry between the front and back films (including width, thickness, and positional deviations), film ghosting, etc. Furthermore, because the thermal expansion coefficients of the gold film coating on the flexible beam do not match those of the quartz material on the flexible beam substrate, thermal stress is introduced, causing changes in the mechanical zero position of the pendulum or changes in the capacitance gap between the pendulum tongue and the upper and lower stators, ultimately altering the accelerometer's zero bias.

[0006] Secondly, poor time stability can easily cause accelerometer output drift. Long-term operation of the pendulum tongue movement or prolonged bending in a certain posture (such as +1g or -1g posture) may cause the gold film coated on the flexible beam of the pendulum to yield (e.g., the yield strength of the gold film is about 80MPa), resulting in temporary or permanent micro-deformation of the entire flexible beam. This creep or fatigue of the flexible beam will affect the accelerometer output.

[0007] To address the aforementioned issues, US Patent US10036765 (Rducing hysteresis effects in an accelerometer) proposed modifying the film material (e.g., adding graphene, molybdenum, tungsten, hafnium, or zirconium) on the existing pendulum flexible beam structure to reduce the linear expansion coefficient of the film material and improve the film's resistance to deformation. However, this approach requires coating different materials onto the pendulum in different areas, and the connection process between the films in different areas is quite complex, involving adjustments to the entire coating process (multiple coatings). Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention proposes a quartz pendulum based on a four-flexible beam structure and its molding method, which can improve the zero-bias stability and time stability of accelerometers.

[0009] One of the above-mentioned objectives of the present invention is achieved by the following technical solution:

[0010] A quartz pendulum structure based on a four-flexible-beam structure includes a pendulum tongue, a support ring, and flexible beams flexibly connecting the pendulum tongue to the support ring. There are four flexible beams arranged in parallel, with two main flexible beams and two auxiliary flexible beams. The two auxiliary flexible beams are positioned between the two main flexible beams or on the outer sides of the two main flexible beams. The width and thickness of the two auxiliary flexible beams are both less than the width and thickness of the two main flexible beams. A gold film is plated on the surface of the two auxiliary flexible beams to electrically connect the gold film on the support ring surface to the gold film on the pendulum tongue surface.

[0011] Furthermore, each of the four flexible beams has a gradually rounded chamfer at its root, with a chamfer radius R of 0.2 to 0.4 mm.

[0012] Moreover, the centers of mass of the four flexible beams are arranged coplanarly in the direction of the sensitive axis of the quartz pendulum.

[0013] Furthermore, the two auxiliary flexible beams are positioned between the two main flexible beams, and the positional distribution of the two auxiliary flexible beams conforms to d = 2e, where d is the distance between the two auxiliary flexible beams and e is the distance between the auxiliary flexible beams and the adjacent main flexible support beam.

[0014] Furthermore, the width of a single main flexible beam is 2.5–3 mm, the length is 2.5–3 mm, the thickness is 0.02–0.03 mm, and the stiffness is 7–10 g / rad; the width of a single auxiliary flexible beam is 0.8–1 mm, the length is 2.5–3 mm, and the thickness is 0.01–0.02 mm.

[0015] Moreover, the width of the gold film on the surface of the two auxiliary flexible beams is 0.4 to 0.6 mm.

[0016] The second objective of this invention is achieved through the following technical solution:

[0017] A method for forming a quartz pendulum structure based on a four-flexible beam structure includes the following steps:

[0018] Step 1: The pendulum plate is shaped by laser cutting, including the production of the support ring, pendulum tongue and flexible beam on the pendulum plate. This step is the shaping process of the pendulum plate. After processing, the three bosses on the support ring and the four flexible beams all have a machining allowance.

[0019] Step 2: Use chemical etching to finish the three bosses and four flexible beams on the support ring to achieve the designed thickness value;

[0020] Step 3: The gold film on the plate is formed in one step by vacuum coating.

[0021] Moreover, step 2 includes:

[0022] 2.1. Cover the area outside the four flexible beams with a mask, erode the four flexible beams, and make the main flexible beams reach the set thickness.

[0023] 2.2 Cover the area outside the two auxiliary flexible beams with a mask, and then continue to etch the two auxiliary flexible beams to the set thickness;

[0024] 2.3. Use a mask to cover only the three protrusion areas on both sides, and continue etching to remove excess material, etching out the thickness of the three protrusions on both sides;

[0025] 2.4. Cover the area outside the two main flexible beams with a mask and continue to erode the main flexible beams to adjust the stiffness and achieve the final design dimensions.

[0026] Furthermore, in step 3, gold film is deposited using electron beam evaporation with a thickness of 200-300 nanometers, and a 10-20 nanometer chromium layer is deposited on both sides of the plate before gold film deposition.

[0027] The advantages and positive effects of this invention are as follows:

[0028] 1. This invention eliminates the influence of thermal stress of the film layer on the main flexible beam by adding two thin and narrow auxiliary flexible beams for gold coating, thereby greatly avoiding the problem of thermal hysteresis in accelerometer output and improving the zero bias stability of accelerometer.

[0029] 2. The present invention uses four flexible beams to prevent the two main flexible beams from being affected by the creep of the gold film layer, and the gradually rounded corners at the root of the flexible beams reduce the stress concentration at sharp corners, thereby suppressing the creep effect of the overall pendulum structure and improving the time stability of the accelerometer.

[0030] 3. Modal simulation of the four flexible beam pendulum of this invention proves that the four-beam structure suppresses higher-order vibration modes, reduces cross-coupling interference, and improves the environmental adaptability of the accelerometer to vibration resistance. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the pendulum structure of a traditional quartz flexible accelerometer;

[0032] Figure 2 This is a schematic diagram of the quartz pendulum based on a four-flexible beam structure according to the present invention;

[0033] Figure 3 This is a partially enlarged view of the four flexible beams of the quartz pendulum plate based on the four flexible beam structure of the present invention;

[0034] Figure 4 This is a diagram of the corrosion process of a quartz pendulum based on a four-flexible beam structure, according to the present invention. Detailed Implementation

[0035] The structure of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that these embodiments are descriptive and not limiting.

[0036] Please refer to the section on a quartz pendulum based on a four-flexible beam structure. Figures 2-4 The invention comprises a swing tongue 4, a support ring 1, and flexible beams flexibly connecting the swing tongue to the support ring. The invention features four flexible beams arranged in parallel. Two of these are main flexible beams, and the other two are auxiliary flexible beams. The two auxiliary flexible beams can be positioned between the two main flexible beams or separately on the outer sides of the two main flexible beams. The two main flexible beams provide primary stiffness and support the swing tongue 4. The two main flexible beams are located on the outer sides of the support ring. Figure 2 and 3 The first two are labeled 13 and 14 respectively; the other two auxiliary flexible beams are used for gold film plating, responsible for establishing an electrical connection between the conductive gold film of the support ring 1 (labeled 8 and 9 in the attached figure) and the conductive gold film 10 of the swing tongue 4. The two auxiliary flexible beams are attached... Figure 2 and 3 The numbers 15 and 16 are used to indicate the gold film on the surfaces of the two auxiliary flexible beams. Figure 2 and 3 The numbers are labeled 11 and 12 respectively.

[0037] The quartz pendulum is made of quartz glass. Gold films are deposited on both sides of the pendulum using vacuum deposition technology. In this embodiment of the invention, electron beam evaporation is used, and the gold film thickness is generally 200 to 300 nanometers. To increase the adhesion of the gold film, a 10 to 20 nanometer chromium layer can be deposited before depositing the gold film. The quartz pendulum forming process is as follows:

[0038] Step 1: The pendulum plate is shaped by laser cutting, including the support ring, pendulum tongue and flexible beam on the pendulum plate. This step is the shaping process of the pendulum plate. After processing, the three protrusions on the support ring (marked by numbers 5, 6 and 7 in the attached figure) and the four flexible beams all have a machining allowance.

[0039] Step 2: Using chemical etching, the two main flexible beams, two auxiliary flexible beams, and three protrusions are precision-machined to achieve the designed thickness, thus adjusting the stiffness of the quartz pendulum. The chemical etching equipment used is an automatic pendulum etching machine, with the temperature of its storage tank set to 40℃ and the robotic arm swing time set to 5 seconds. The etching process is as follows: Figure 4As shown, the main technical points are as follows: First, by covering the area outside the four flexible beams with a mask, the four flexible beams are etched to achieve the set thickness of the main flexible beams; then, by covering the area outside the two auxiliary flexible beams with a mask, the two auxiliary flexible beams are etched to the set thickness; next, by covering only the three boss areas on both sides with a mask, the thickness of the three bosses on both sides is etched out; finally, by covering the area outside the two main flexible beams with a mask, the main flexible beams are etched (thickness direction removal) to adjust the stiffness and achieve the final design dimensions. Secondly, regarding the selection of the etching solution, HF, HF+CH3COOH, NH4HF2, and NH4F+HF solutions are commonly used for etching quartz materials. The etching solution should have a uniform etching rate to facilitate quality control and minimal corrosion of the protective mask. This invention selects HF+CH3COOH solution as the etching solution, with a volume ratio of 7:3, which meets the above requirements. Thirdly, regarding the selection of the mask protection method, the protective film should be customizable in shape, easy to operate, and able to withstand strong acid etching. This invention selects fluorosilicone rubber, which is resistant to strong acid etching. After immersion in the etching solution for 10 hours, it only produces slight swelling (i.e., etching), and the etched edges are very neat.

[0040] Step 3: The gold film on the plate is formed in one step by vacuum coating.

[0041] The advantages of this invention, without significantly altering the pendulum forming process, are as follows: First, by setting two thin and narrow auxiliary flexible beams 15 and 16 for coating gold films 11 and 12, even if thermal stress in the film layer exists due to coating errors and mismatches in the linear expansion coefficients of the materials, the thinness and narrowness of the auxiliary flexible beams 15 and 16, along with the narrowness of the gold films 11 and 12, greatly reduces the impact on the main flexible beams 13 and 14 and the overall pendulum structure. This significantly avoids the problem of thermal hysteresis in the accelerometer output and improves the zero-bias stability of the accelerometer. Second, the use of four flexible beams, especially the two main flexible beams 13 and 14, which are no longer affected by the creep of the gold film layer, and the gradual rounded corners at the roots of the flexible beams to reduce stress concentration at sharp corners, suppresses the creep effect of the overall pendulum structure and improves the temporal stability of the accelerometer. Third, by ensuring that the centroids of the four flexible beams are coplanar in the direction of the sensitive axis during the processing, the cross-coupling interference is reduced; the modal simulation of the four flexible beam pendulum proves that the four-beam structure suppresses high-order vibration modes. As shown in Table 1, the modal analysis of the pendulum was carried out by finite element simulation software. Among them, the four-beam structure has a significant improvement in the vibration frequencies above the fourth order compared with the double-beam structure, which improves the environmental adaptability of the accelerometer to vibration resistance and other aspects.

[0042] Table 1 Comparison of pendulum resonant frequencies

[0043]

[0044] Figure 3This is a partial schematic diagram of the quartz pendulum flexible beam structure with four flexible beams provided in this embodiment of the invention. The length b, width a, and thickness of the two main flexible beams 13 and 14 are mainly calculated based on the main stiffness requirements of the flexible beam. In this embodiment, the width a of a single main flexible beam is (2.5~3) mm, the length b is (2.5~3) mm, the thickness is (0.02~0.03) mm, and the stiffness is approximately (7~10) g / rad. Two auxiliary flexible beams 15 and 16 are located between the two main flexible beams 13 and 14, with their positions distributed according to d = 2e, where d is the distance between the two auxiliary flexible beams and e is the distance between the auxiliary flexible beams and the adjacent main flexible support beams. The two auxiliary flexible beams 15 and 16 are narrower and thinner than the main flexible beams, and are coated with a gold film, responsible for electrically connecting the support ring to the gold film on the swing tongue. In this embodiment, the width c of a single auxiliary flexible beam is (0.8–1) mm, the length b is (2.5–3) mm, the thickness is (0.01–0.02) mm, and the gold film width f is (0.4–0.6) mm. The roots of the four flexible beams have gradually rounded chamfers, with the chamfer radius R typically taken as (0.2–0.4) mm to avoid stress concentration at sharp corners. During processing, it is essential to ensure that the centers of mass of the four flexible beams are coplanar in the direction of the sensitive axis (acceleration input sensitive axis direction), thereby reducing the influence of cross-coupling.

[0045] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A quartz pendulum structure based on a four-flexible beam structure, comprising a pendulum tongue, a support ring, and a flexible beam flexibly connecting the pendulum tongue to the support ring; characterized in that: The flexible beams consist of four parallel beams. Two of them are main flexible beams, and the other two are auxiliary flexible beams. The two auxiliary flexible beams are positioned between the two main flexible beams or on the outer sides of the two main flexible beams. The width and thickness of the two auxiliary flexible beams are both less than the width and thickness of the two main flexible beams. A gold film is plated on the surface of the two auxiliary flexible beams to electrically connect the gold film on the surface of the support ring to the gold film on the surface of the swing tongue.

2. The quartz pendulum structure based on a four-flexible beam structure according to claim 1, characterized in that: A gradually rounded chamfer is provided at the root of each of the four flexible beams, with the chamfer radius R ranging from 0.2 to 0.4 mm.

3. The quartz pendulum structure based on a four-flexible beam structure according to claim 1, characterized in that: The centers of mass of the four flexible beams are arranged in a coplanar manner along the sensitive axis of the quartz pendulum.

4. The quartz pendulum structure based on a four-flexible beam structure according to claim 1, characterized in that: The two auxiliary flexible beams are positioned between the two main flexible beams, and the positions of the two auxiliary flexible beams are distributed in accordance with d = 2e, where d is the distance between the two auxiliary flexible beams and e is the distance between the auxiliary flexible beams and the adjacent main flexible support beam.

5. The quartz pendulum structure based on a four-flexible beam structure according to claim 1, characterized in that: The width of a single main flexible beam is 2.5–3 mm, the length is 2.5–3 mm, the thickness is 0.02–0.03 mm, and the stiffness is 7–10 g / rad; the width of a single auxiliary flexible beam is 0.8–1 mm, the length is 2.5–3 mm, and the thickness is 0.01–0.02 mm.

6. A method for forming a quartz pendulum structure based on a four-flexible beam structure according to any one of claims 1-5, comprising the following steps: Step 1: The pendulum plate is shaped by laser cutting, including the production of the support ring, pendulum tongue and flexible beam on the pendulum plate. This step is the shaping process of the pendulum plate. After processing, the three bosses on the support ring and the four flexible beams all have a machining allowance. Step 2: Use chemical etching to finish the three bosses and four flexible beams on the support ring to achieve the designed thickness value; Step 3: The gold film on the plate is formed in one step by vacuum coating.

7. The molding method for a quartz pendulum structure based on a four-flexible beam structure according to claim 6, characterized in that: Step 2 includes: 2.

1. Cover the area outside the four flexible beams with a mask, erode the four flexible beams, and make the main flexible beams reach the set thickness. 2.2 Cover the area outside the two auxiliary flexible beams with a mask, and then continue to etch the two auxiliary flexible beams to the set thickness; 2.

3. Use a mask to cover only the three protrusion areas on both sides, and continue etching to remove excess material, etching out the thickness of the three protrusions on both sides; 2.

4. Cover the area outside the two main flexible beams with a mask and continue to erode the main flexible beams to adjust the stiffness and achieve the final design dimensions.

8. The molding method for a quartz pendulum structure based on a four-flexible beam structure according to claim 6, characterized in that: In step 3, gold film is deposited using electron beam evaporation with a thickness of 200-300 nanometers. Before depositing the gold film, a 10-20 nanometer chromium layer is deposited on both sides of the plate.

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