Quartz pendulous reed based on four-flexible-beam structure and forming method thereof

Abstract

The invention relates to a quartz pendulous reed based on a four-flexible-beam structure and a forming method of the quartz pendulous reed, the quartz pendulous reed comprises a pendulous tongue, a supporting ring and four flexible beams for flexibly connecting the pendulous tongue into the supporting ring, the number of the flexible beams is four, the four flexible beams are arranged in parallel, and two main flexible beams provide main rigidity and are responsible for supporting the pendulous tongue; and the other two auxiliary flexible beams are relatively thin and narrow and are used for electrically connecting the supporting ring with the gold film on the surface of the swing tongue. On one hand, the influence of thermal stress caused by mismatching of thermal expansion coefficients of a pendulous reed material and a film layer material is inhibited by designing the auxiliary flexible beam structure; and on the other hand, the two main flexible beams are not influenced by creep deformation of the gold film layer any more, sharp corner stress concentration and the like are reduced through the arrangement of the gradually-changed round corners at the roots of the flexible beams, the problem of micro yield creep deformation of the flexible beams caused by long-term placement in a fixed posture and the like is solved, and then the temperature stability and the time stability of the quartz flexible accelerometer are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of inertial sensors, and in particular relates to a quartz pendulum piece based on a four-flexible beam structure and a forming method thereof. Background Art

[0002] Quartz flexure accelerometers are the simplest, high-precision accelerometers currently used in domestic inertial navigation and guidance systems. As system requirements increase, accelerometers must exhibit extremely high stability over long periods of time and across the entire temperature range, while also meeting environmental requirements for shock, vibration, high humidity, and high heat.

[0003] The quartz flexible accelerometer uses a flexible support to detect sensitive mass, a capacitor to detect displacement changes, and a permanent magnet torquer to generate inertia torque to achieve 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, which includes a pendulum tongue 4 (the sensitive detection mass part, which is the active 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 arranged axially on the support ring, conductive gold films 8 and 9 on the support ring, conductive gold film 10 on the pendulum tongue, conductive gold films 11 and 12 on the flexible beams, and the same gold film is symmetrically distributed on the other side of the pendulum (not shown in this figure). The pendulum tongue is allowed to swing along the input sensitive axis (perpendicular to the paper). Generally speaking, the pendulum material is quartz glass, and the linear expansion coefficient is 0.54×10 -6 / ℃. On both sides of the pendulum, a conductive metal film layer is formed in a specific area of ​​the pendulum tongue by vacuum coating technology, thereby forming the dynamic plate of the flat-plate capacitor; a conductive metal film layer and necessary conductive pads are formed in a specific area of ​​the support ring, and these pads are responsible for electrically connecting with the pins on the accelerometer through gold wires. Some examples of flexible beams may include at least one thin film lead, which can establish an electrical connection between the conductive film layer of the support ring and the conductive film layer of the pendulum tongue; the lead is generally a gold film coated on the surface of the flexible beam by vacuum coating technology, and the linear expansion coefficient of gold is 14.2×10 -6 / ℃.

[0004] Existing quartz flexible accelerometer pendulums mostly use a double flexible beam symmetrical structure, such as Figure 1 As shown in the figure, it realizes acceleration sensitivity by supporting the swing tongue with dual beams. The dual beams are coated with gold film to provide electrical connection between the support ring and the swing tongue. However, there are the following problems:

[0005] First, the accelerometer output produces temperature hysteresis. During the manufacturing and working process of the accelerometer, due to the effect of temperature, its output is unstable or produces temperature hysteresis effect, and it may even be unable to return to zero position after the temperature change ends. For the pendulum, one of the main factors affecting this effect is the inevitable processing error of the gold film plated on the surface of the flexible beam, such as asymmetry of the positive and negative film layers (including width, thickness and position deviation, etc.), film layer ghosting, etc., and because the thermal expansion coefficient of the gold film plated on the flexible beam does not match that of the flexible beam base quartz material, thermal stress is introduced, causing the mechanical zero position of the pendulum to change or the capacitance gap between the pendulum tongue and the upper and lower stators to change, which ultimately changes the zero bias of the accelerometer;

[0006] Second, poor temporal stability can easily cause accelerometer output drift. Long-term pendulum movement or prolonged bending in a certain posture (such as +1g or -1g) can cause the gold film coating on the pendulum's flexible beam to yield (the yield strength of the gold film is approximately 80MPa), resulting in temporary or permanent micro-deformation of the entire flexible beam. This creep or fatigue of the flexible beam can affect the accelerometer's output.

[0007] In order to solve the above problems, U.S. Patent US10036765 (Rducing hysteresis effects in an accelerometer) was retrieved, which proposed changing the membrane material (such as adding graphene, molybdenum, tungsten, hafnium or zirconium, etc.) on the basis of the existing pendulum flexible beam structure to reduce the linear expansion coefficient of the membrane material and improve the membrane's resistance to deformation. However, this solution requires coating membranes of different materials in different areas on the pendulum, and the connection process between membrane layers in different areas is relatively complicated, involving adjustments to the entire coating process (multiple coatings), etc. Summary of the Invention

[0008] In view of the deficiencies in the prior art, the present invention proposes a quartz pendulum based on a four-flexure beam structure and a forming method thereof, which can improve the zero bias stability and time stability of the accelerometer.

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

[0010] A quartz pendulum structure based on a four-flexible beam structure, comprising a pendulum tongue, a support ring, and a flexible beam that flexibly connects the pendulum tongue to the support ring; there are four flexible beams, and the four flexible beams are arranged in parallel, wherein two flexible beams are main flexible beams, and the other two flexible beams are auxiliary flexible beams, and the two auxiliary flexible beams are arranged between the two main flexible beams or respectively on the outside of the two main flexible beams; the width of the two auxiliary flexible beams is smaller than the width of the two main flexible beams, and the thickness of the two auxiliary flexible beams is smaller than the thickness of the two main flexible beams; the surfaces of the two auxiliary flexible beams are coated with a gold film, which is used to electrically connect the gold film on the surface of the support ring with the gold film on the surface of the pendulum tongue.

[0011] Moreover, the roots of the four flexible beams are all provided with a gradual round chamfer, and the round chamfer radius R is 0.2 to 0.4 mm.

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

[0013] Moreover, the two auxiliary flexible beams are arranged between the two main flexible beams, and the position 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 beam and the main flexible support beam on the adjacent side.

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

[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 object of the present invention is achieved by the following technical solutions:

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

[0018] Step 1: Laser cutting is used to shape the pendulum piece, including processing the support ring, swing tongue and flexible beam on the pendulum piece. This step is the shaping of the pendulum piece. After processing, the three bosses on the support ring and the four flexible beams are left with a finishing allowance.

[0019] Step 2: Finish the three bosses and four flexible beams on the support ring by chemical etching to achieve the designed thickness.

[0020] Step 3: Form the gold film on the pendulum piece through vacuum coating in one step.

[0021] Furthermore, the step 2 includes:

[0022] 2.1. Cover the area outside the four flexible beams with a mask and etch the four flexible beams to make the main flexible beam 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 boss areas on both sides, and continue etching to remove the thickness of the three bosses on both sides;

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

[0026] Moreover, in the step 3, the gold film is plated by electron beam evaporation, the thickness of the gold film is 200-300 nanometers, and a 10-20 nanometer chromium layer is plated on both sides of the swing plate before the gold film is plated.

[0027] The advantages and positive effects of the present invention are:

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

[0029] 2. The present invention sets four flexible beams so that the two main flexible beams are no longer affected by the creep of the gold film layer, and the gradual rounded corner setting at the root of the flexible beam reduces the stress concentration at the sharp corner, thereby suppressing the creep effect of the overall pendulum structure and improving the time stability of the accelerometer.

[0030] 3. The modal simulation of the four-flexible beam pendulum of the present invention proves that the four-beam structure suppresses high-order vibration modes, reduces cross-coupling interference, and improves the environmental adaptability of the accelerometer such as anti-vibration. BRIEF DESCRIPTION OF THE DRAWINGS

[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 structural diagram of a quartz pendulum based on a four-flexible beam structure according to the present invention;

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

[0034] Figure 4 This is a diagram of the corrosion process of the quartz pendulum based on the four-flexible beam structure of the present invention. DETAILED DESCRIPTION

[0035] The structure of the present invention will be further described below with reference to the accompanying drawings and through examples. It should be noted that the present examples are descriptive rather than restrictive.

[0036] A quartz pendulum based on a four-flexure beam structure, see Figure 2-Figure 4 , comprising a swing tongue 4, a support ring 1 and a flexible beam that flexibly connects the swing tongue to the support ring. The invention point is: there are four flexible beams, which are arranged in parallel. Among them, two flexible beams are main flexible beams, and the other two flexible beams are auxiliary flexible beams. The two auxiliary flexible beams can be arranged between the two main flexible beams or on the outside of the two flexible beams. The two main flexible beams provide the main stiffness and are responsible for supporting the swing tongue 4. The two main flexible beams are attached to the Figure 2 and 3 The other two auxiliary flexible beams are used for gold film plating and are responsible for establishing electrical connection between the conductive gold film of the support ring 1 (labeled as 8 and 9 in the figure) and the conductive gold film 10 of the swing tongue 4. Figure 2 and 3 The gold films on the surfaces of the two auxiliary flexible beams are marked with 15 and 16 respectively. Figure 2 and 3 They are marked with 11 and 12 respectively.

[0037] The quartz pendulum is made of quartz glass. Both sides of the pendulum are coated with gold via vacuum coating technology. In this embodiment, electron beam evaporation is used. The thickness of the gold film is generally 200 to 300 nanometers. To increase the adhesion of the gold film, a 10 to 20 nanometer chromium layer can be applied before the gold film is plated. The quartz pendulum molding process is as follows:

[0038] Step 1: Laser cutting is used to form the pendulum piece, including processing the support ring, swing tongue and flexible beam on the pendulum piece. This step is the forming process of the pendulum piece. After processing, the three bosses on the support ring (marked with numbers 5, 6 and 7 in the accompanying drawings) and the four flexible beams are left with finishing allowances;

[0039] Step 2: Use chemical etching to fine-process the two main flexible beams, two auxiliary flexible beams and three protrusions to achieve the designed thickness value and realize the stiffness adjustment of the quartz pendulum. The equipment used for chemical etching is an automatic pendulum etching machine, and the temperature of its liquid storage tank is set to 40℃ and the swing time of the robot arm is set to 5s. Figure 4As shown, the main technical points are: first, cover the area outside the four flexible beams with a mask, corrode the four flexible beams, and make the main flexible beam reach the set thickness; then cover the area outside the two auxiliary flexible beams with a mask, and continue to corrode the two auxiliary flexible beams to the set thickness; again use the mask to cover only the three boss areas on both sides, continue to corrode and remove the amount, and corrode the thickness of three bosses on two sides; finally, cover the area outside the two main flexible beams with a mask, continue to corrode the main flexible beam (remove in the thickness direction), adjust the stiffness, and reach the final design size. Second, the selection of etching solution. Currently, HF, HF+CH3COOH, NH4HF2, and NH4F+HF solutions are commonly used to etch quartz materials. The etching solution requires: a uniform etching rate to facilitate the control of etching quality, and minimal corrosion to the protective mask. The present invention selects HF+CH3COOH solution as the etching solution, with a ratio (volume ratio) of 7:3 to meet the above requirements. Third, the selection of the mask protection method requires that the shape of the protective film can be processed as needed, the operation is convenient, and it can withstand strong acid etching. The present invention selects fluorosilicone rubber, which is resistant to strong acid etching and only slightly swells (i.e., etches) after immersion in the etching solution for 10 hours, and the etched edges are very neat.

[0040] Step 3: Form the gold film on the pendulum piece through vacuum coating in one step.

[0041] On the basis of basically not changing the swing piece forming process, the advantages of the design of the present invention are: First, by setting two thin and narrow auxiliary flexible beams 15 and 16 for plating the gold films 11 and 12, even if there is thermal stress in the film layer due to coating errors and mismatch of material linear expansion coefficients, the auxiliary flexible beams 15 and 16 are thin and narrow, and the gold films 11 and 12 plated thereon are relatively narrow, so the impact on the main flexible beams 13 and 14 and the overall swing piece structure is greatly reduced, thereby greatly avoiding the problem of thermal lag in the accelerometer output and improving the zero bias stability of the accelerometer. Second, by setting up four flexible beams, especially the two main flexible beams 13 and 14 are no longer affected by the creep of the gold film layer, and the gradual rounded corner setting at the root of the flexible beam reduces the stress concentration at the sharp corner, etc., the creep effect of the overall swing piece structure is suppressed, and the time stability of the accelerometer is improved. Third, by ensuring that the centroids of the four flexible beams are coplanar in the direction of the sensitive axis during the processing, 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 using finite element simulation software. Among them, the four-beam structure has a significantly improved high-order vibration frequency above the fourth order compared with the double-beam structure, which improves the accelerometer's anti-vibration and other environmental adaptability.

[0042] Table 1 Comparison of pendulum resonance frequencies

[0043]

[0044] Figure 3This is a partial schematic diagram of the four-flexible beam structure of the quartz pendulum provided by an embodiment of the present invention. The length b, width a, and thickness of the two main flexible beams 13 and 14 are calculated primarily based on the required main stiffness of the flexible beams. 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. The two auxiliary flexible beams 15 and 16 are located between the two main flexible beams 13 and 14, with a position distribution consistent with d = 2e, where d is the distance between the two auxiliary flexible beams and e is the distance between the auxiliary flexible beam and the adjacent main flexible support beam. 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 bases of the four flexible beams are provided with a gradually rounded chamfer, with a radius R generally set at (0.2-0.4) mm to avoid stress concentration at sharp corners. During processing, the centers of mass of the four flexible beams must be coplanar along the sensitive axis (the acceleration input sensitive axis) to minimize cross-coupling effects.

[0045] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various replacements, changes and modifications are possible without departing from the spirit 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: There are four flexible beams, which are arranged in parallel. Among them, two flexible beams are main flexible beams, and the other two flexible beams are auxiliary flexible beams. The two auxiliary flexible beams are arranged between the two main flexible beams or respectively arranged on the outside of the two main flexible beams; the width of the two auxiliary flexible beams is smaller than the width of the two main flexible beams, and the thickness of the two auxiliary flexible beams is smaller than the thickness of the two main flexible beams; the surface of the two auxiliary flexible beams is plated with gold film, which is used to electrically connect the gold film on the surface of the support ring with 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: The roots of the four flexible beams are all provided with a gradual round chamfer, and the round chamfer radius R is 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 centroids of the four flexible beams are coplanarly arranged in the direction of 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 arranged between the two main flexible beams, and the position distribution of the two auxiliary flexible beams conforms to d=2e, wherein d is the distance between the two auxiliary flexible beams, and e is the distance between the auxiliary flexible beam and the main flexible support beam on the adjacent side.

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 to 5, comprising the following steps: Step 1: Laser cutting is used to shape the pendulum piece, including processing the support ring, swing tongue and flexible beam on the pendulum piece. This step is the shaping of the pendulum piece. After processing, the three bosses on the support ring and the four flexible beams are left with a finishing allowance. Step 2: Finish the three bosses and four flexible beams on the support ring by chemical etching to achieve the designed thickness. Step 3: Form the gold film on the pendulum piece through vacuum coating in one step.

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

1. Cover the area outside the four flexible beams with a mask and etch the four flexible beams to make the main flexible beam 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 boss areas on both sides, and continue etching to remove the thickness of the three bosses on both sides; 2.

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

8. The method for forming a quartz pendulum structure based on a four-flexible beam structure according to claim 6, characterized in that: In the step 3, a gold film is plated by electron beam evaporation, the thickness of the gold film is 200-300 nanometers, and a 10-20 nanometer chromium layer is plated on both sides of the pendulum before the gold film is plated.

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