MEMS friction sensor for measuring friction on rough surface and its manufacturing and design method

Abstract

The present invention belongs to the technical field of micro-electromechanical systems, and discloses a MEMS friction sensor for measuring friction on a rough surface and a method for making and designing the same. The MEMS friction sensor is decomposed into a floating element, a silicon microstructure, an electrode substrate, an interface circuit, and a packaging shell, which are then processed and assembled separately. The manufacturing method includes a micro-assembly device and a micro-assembly method. The design method includes mechanical analysis, mechanical calculation, process design, and displacement calculation. The MEMS friction sensor for measuring friction on a rough surface of the present invention and a method for making and designing the same realize the complex environment measurement capability of the MEMS friction sensor, with a measurement range of 0 to 100 Pa, a resolution of 0.1 Pa, and a measurement bandwidth of 0 to 200 Hz. It has the characteristics of small size, good temperature stability, and high reliability, and can accurately measure the surface friction resistance of complex aerodynamic shapes.

Description

Technical Field

[0001] The invention belongs to the technical field of micro-electromechanical systems, and in particular relates to a MEMS friction sensor for measuring the friction of a rough surface and a manufacturing and design method thereof. Background Art

[0002] MEMS friction sensors are mainly used to test the surface friction resistance of aircraft, and then determine the size and distribution of the surface friction resistance of aircraft, which is of great significance to aircraft design. Traditional surface friction resistance test devices are mainly micro-strain friction resistance balances, but they are limited by factors such as sensitivity, temperature, volume and cost, and are difficult to be widely used in the field of aircraft design. MEMS friction sensors based on micro-electromechanical system technology have outstanding advantages such as small size, low cost and high reliability, and can be widely used in fields such as aircraft design.

[0003] At present, MEMS friction sensors are divided into comb capacitive and piezoresistive types, which are mainly used in surface friction measurement tests in low-speed wind tunnels. In 2001, Jiang Zhe et al. [A MEMS device for measurement of skinfriction with capacitive sensing, Microelectromechanical Systems Conference, 24~26 August, 2001[C].] designed a cantilever beam-supported flat plate differential capacitive MEMS friction sensor with a measurement range of only 0.1~2Pa, which is suitable for low-speed wind tunnels. In 2011, Jessica Meloy et al. [Experimental verification of a MEMS based skin friction sensor for quantitative wall shearstress measurement, 41st AIAA Fluid Dynamics Conference and Exhibit, 27~30June 2011, Honolulu, Hawaii[C].] designed a four-beam supported comb-tooth capacitive MEMS friction sensor with a measurement range of 0.1~5Pa. In order not to destroy the flow field, the floating element and the comb-tooth capacitor must be exposed to the wind tunnel flow field. It is only suitable for low-speed wind tunnels with high gas purity.

[0004] However, many applications require surface friction resistance testing in hypersonic wind tunnel flow fields. Currently, the test of model surface friction resistance in hypersonic wind tunnel flow fields still uses traditional micro friction resistance balances. In 2010, Joseph A. Schetz et al. [Direct measurement of skin friction in complex flows, 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition 4~7 January 2010, Orlando, Florida [C].] developed a strain gauge micro friction resistance balance to measure model surface friction resistance in a hypersonic wind tunnel flow field at Ma=4. However, this micro balance has low sensitivity, poor temperature stability, and a large volume, and cannot be used to accurately measure the distribution of aircraft surface friction resistance. Moreover, the normal load in the hypersonic wind tunnel flow field is large, which puts higher requirements on the design and development of MEMS friction resistance sensors.

[0005] In 2014, the Chinese Patent Literature Library published an invention by the inventor team entitled "A micromechanical friction sensor and its fabrication method" (ZL201418003582.X). The floating element of the micromechanical friction sensor, i.e., the MEMS friction sensor, is connected to an elastic beam structure with a sensitive capacitor element through a support rod. The surface friction resistance felt by the floating element is transmitted to the elastic beam structure through the support rod, driving the sensitive capacitor vibrating plates on both sides of the elastic beam to deflect. The measured surface friction resistance can be solved by the difference of the sensitive capacitors on both sides. The results of the static calibration of the prototype and the hypersonic wind tunnel verification test show that the MEMS friction sensor has high sensitivity and good stability, and the header structure and packaging form are suitable for the hypersonic wind tunnel test environment [Fabrication, calibration and proof experiments in hypersonic wind tunnelfor a novel MEMS skin friction sensor, Microsystem Technologies, vol.23,No.8, 2017 [J].].

[0006] In 2022, the China Patent Literature Library disclosed the invention of the inventor team as a high-frequency response, large-range MEMS friction sensor (ZL202210154250.5). The measurement bandwidth of this MEMS friction sensor is greater than 3000Hz, the measurement range is 0~1500Pa, and the resolution is better than 2Pa. It is suitable for shock wave wind tunnels with millisecond operating times and high-temperature arc wind tunnels with second operating times.

[0007] With the rapid development of hypersonic technology, the aerodynamic shape and thermal protection structure design of aircraft in engineering are becoming more and more complex. Most of the surfaces to be measured on aircraft are no longer simple smooth surfaces, but have a certain rough texture. The surfaces to be measured of the aforementioned MEMS friction sensors are all smooth surfaces (201418003582.X; ZL202210154250.5), which cannot meet the requirements of accurate measurement.

[0008] Currently, there is an urgent need to develop a MEMS friction sensor suitable for measuring the friction resistance of rough textured material surfaces in hypersonic wind tunnel flow fields, as well as a manufacturing method and a design method thereof. Summary of the invention

[0009] One technical problem to be solved by the present invention is to provide a MEMS friction sensor for measuring the friction of a rough surface. Another technical problem to be solved by the present invention is to provide a method for manufacturing a MEMS friction sensor for measuring the friction of a rough surface. Still another technical problem to be solved by the present invention is to provide a method for designing a MEMS friction sensor for measuring the friction of a rough surface, so as to overcome the shortcomings of existing MEMS friction sensors.

[0010] The MEMS friction sensor for measuring the friction of a rough surface of the present invention is characterized in that the MEMS friction sensor comprises a packaging cover plate, a meter head structure, an interface circuit and a packaging tube shell;

[0011] The package tube shell comprises a package cover plate and a package tube seat stacked in sequence from top to bottom; the package tube seat is cylindrical, and a groove is arranged on the surface; a package positioning boss is arranged on the upper surface of the package tube seat along the periphery of the groove, a circular adapter is mounted on the package positioning boss, and a stepped circular tube-shaped package cover plate is mounted outside the adapter, the bottom surface diameter of the package cover plate is equal to the top surface diameter of the package tube seat, and the top surface diameter of the package cover plate is smaller than the top surface diameter of the package tube seat; a meter head structure and an interface circuit are installed in the stepped cylindrical central cavity of the package cover plate;

[0012] The meter head structure includes a floating element, a silicon microstructure and an electrode substrate. The meter head structure is used to sense the friction resistance on the surface of the aircraft model and convert it into a differential capacitance signal. The floating element includes a centrally symmetrical disc-shaped probe, a support rod and a positioning step connected in sequence from top to bottom. The probe and the packaging cover plate are flush with the surface of the aircraft model. The surfaces of the probe and the packaging cover plate have a continuous surface texture. There is an annular gap between the probe and the packaging cover plate. The probe senses the friction resistance on the surface of the aircraft model. The support rod converts the friction resistance into a friction resistance torque and transmits it to the silicon microstructure through the positioning step. The positioning step is used to determine the position of the floating element in the vertical direction of the silicon microstructure.

[0013] The silicon microstructure includes an elastic beam, a vibration pole plate and a support frame; the support frame is a square flat plate, and continuous cutting is performed on the support frame to obtain a Chinese-character shaped component at the center; the parts extending from the left and right ends of the Chinese-character shaped component are left-right symmetrical elastic beams, and the elastic beams are fixed beams at both ends. The torsional stiffness of the elastic beams is less than the normal stiffness, and mainly torsional deformation occurs when inducing friction resistance; the middle part of the Chinese-character shaped component is a vibration pole plate that is symmetrical up and down relative to the elastic beam; a through hole corresponding to the positioning step is arranged at the center of the vibration pole plate; a probe installation alignment line is arranged on the upper surface of the support frame; the support frame supports the vibration pole plate and the floating element through the elastic beam;

[0014] The electrode substrate includes a lead electrode, a glass boss and a gold electrode; the upper surface of the electrode substrate is provided with two gold electrodes symmetrically arranged in the upper and lower directions corresponding to the vibration pole plate, each gold electrode extends to the left and right respectively, and the extended part forms a lead electrode, and a glass boss is arranged in the remaining area of ​​the upper surface of the electrode substrate; the gold electrode and the vibration pole plate of the silicon microstructure together constitute a sensitive capacitor element; the glass boss is anodically bonded to the supporting frame of the silicon microstructure, and the height of the glass boss is the capacitor gap constituting the sensitive capacitor. h 0; the upper surface of the electrode substrate is engraved with alignment lines I and II;

[0015] The interface circuit includes a circuit substrate, which is placed in a groove of a packaging tube seat. A number of electronic components and solder pads are arranged on the circuit substrate, and the solder pads are used to connect to the lead electrodes of the electrode substrate. The upper surface of the circuit substrate is engraved with a silicon capacitor installation alignment line corresponding to the alignment line I of the electrode substrate, and a floating element installation alignment line corresponding to the alignment line II of the electrode substrate.

[0016] Furthermore, one processing method for the continuous surface texture on the surface of the probe and the packaging cover plate is to use an adapter to fix the probe and the packaging cover plate on the same processing surface for synchronous engraving, and another processing method is to stick a material layer consistent with the surface material of the aircraft model on the surface of the probe and the packaging cover plate.

[0017] Furthermore, the silicon microstructure is processed by deep reactive ion etching technology of single crystal silicon material; the electrode substrate is made by Pyrex glass wet etching and metal deposition technology; the interface circuit is made by ceramic-based precision microstrip circuit technology; the floating element is processed by a duralumin material precision instrument lathe, and the package shell is processed by duralumin material precision machinery;

[0018] Ceramic-based precision microstrip circuit technology uses a ceramic-based precision circuit substrate and is manufactured using a precision ceramic microstrip circuit process. The precision ceramic microstrip circuit process includes substrate cutting, double-sided metal sputtering, electroplating metal thickening and photolithography etching.

[0019] Furthermore, the alignment line I is aligned with the silicon capacitor installation alignment line, and the alignment line II is aligned with the floating element installation alignment line, so as to ensure that the surface textures of the probe and the packaging cover are continuous after installation.

[0020] Furthermore, the electronic components arranged on the interface circuit include a capacitance detection chip AD7747, a single-chip microcomputer C8051F411, an FPC seat and a peripheral circuit; the capacitance detection chip AD7747 converts the differential capacitance signal into a digital signal; the single-chip microcomputer C8051F411 controls the working state of AD7747 and receives the capacitance value collected in real time by AD7747, and sends the capacitance value to the host computer for subsequent processing; the host computer is programmed using Labwindows CVI; the data acquisition update rate of the interface circuit is 20Hz, and the capacitance resolution is 4.99×10 ~4 pF.

[0021] The method for manufacturing a MEMS friction sensor for measuring friction of a rough surface of the present invention comprises the following steps:

[0022] S11. Based on the design indicators of the MEMS friction sensor, use CFD software to optimize the design of each component and circuit of the MEMS friction sensor;

[0023] S12. Processing the components of the MEMS friction sensor separately;

[0024] S13. Assembling silicon microstructure and electrode substrate;

[0025] Under the precision vision equipment, the interface circuit is fixed at position I on the three-degree-of-freedom micro-operation alignment platform; the alignment line I of the electrode substrate is aligned with the silicon capacitor installation alignment line on the interface circuit, the alignment line II of the electrode substrate is aligned with the floating element installation alignment line on the interface circuit, and the electrode substrate is fixed to the interface circuit with epoxy resin; then the silicon microstructure is aligned with the electrode substrate, and the silicon microstructure is fixed to the electrode substrate with epoxy resin;

[0026] S14. Assemble the floating element;

[0027] Under the precision visual equipment, the positioning step of the floating element is inserted into the through hole of the vibrating plate of the silicon microstructure, and then the texture direction of the probe is rotated to the probe installation alignment line on the upper surface of the support frame of the silicon microstructure, and finally the positioning step is fixed by epoxy resin to obtain an assembly;

[0028] S15. Fixed package socket;

[0029] Fix the packaged tube holder on position II of the three-degree-of-freedom micro-operation alignment platform;

[0030] S16. Identify the installation position of the package cover;

[0031] The package cover plate is mounted on the package tube holder to ensure that there is no step on the side of the package tube holder; the package cover plate is photographed by using the visual precision positioning system of the precision visual equipment, and the position of the circular hole on the surface of the package cover plate is identified by the image recognition system;

[0032] S17. Assemble the components;

[0033] Remove the package cover plate, place the interface circuit of the assembly in the groove of the package socket, clamp the assembly with a vacuum suction head, use the visual precision positioning system and the vacuum suction head to move the assembly in the groove, align the probe with the circular hole on the surface of the package cover plate, and fix the assembly on the package socket with epoxy resin;

[0034] S18. Welding circuit;

[0035] Welding the lead wire between the lead electrode and the pad by spot welding;

[0036] S19. Assemble the package cover;

[0037] Put the adapter on the package positioning boss of the package tube holder, then put the package cover on the adapter, make sure that the package cover is coaxial with the probe, and complete the assembly of the MEMS friction sensor.

[0038] The design method of the MEMS friction sensor for measuring the friction of a rough surface of the present invention comprises the following steps:

[0039] S21. Mechanical analysis;

[0040] Probe Sensing and Surface Area A Proportional to and perpendicular to x Frictional resistance in the axial direction f s , the support rod will reduce the friction resistance f s Converted into friction torque T s , friction resistance torque Ts The elastic beam fixed at both ends is torsionally deformed, and the vibrating pole plate rigidly connected to the elastic beam is torsionally deformed. y Twist angle of shaft θ , the sensitive capacitance on both sides of the elastic beam C 1 and sensitive capacitor C 2 changes; the sensitive capacitance on both sides of the elastic beam is calculated by differential C 1 and sensitive capacitor C 2 The change of Δ C , and then calculate the friction resistance sensed by the probe f s ;

[0041] S22. Mechanical calculation;

[0042] The surface friction resistance sensed by the probe is proportional to the area. f s It can be expressed as:

[0043] ;

[0044] in, A is the surface area of ​​the probe, is the friction resistance per unit area;

[0045] Frictional resistance torque transmitted to the elastic beam T s :

[0046] ;

[0047] in, h 2 is the distance between the upper surface of the probe and the center line of the torsion axis;

[0048] Torsional elastic coefficient of elastic beam K :

[0049] ;

[0050] in, G is the shear elastic modulus of single crystal silicon; I p is the cross-sectional polar moment of inertia of the elastic beam, , w , h , l 1 are the width, thickness and length of the elastic beam, β is the torsion coefficient of the rectangular section, ;

[0051] The friction torque of the vibrating plate T sA certain torsion angle is generated under the action θ :

[0052] ;

[0053] It can be seen that the torsion angle θ With friction resistance f s is proportional to;

[0054] Vibrating pole plate produces torsion angle θ The differential sensing capacitance Δ C :

[0055] ;

[0056] in, h 0 is the initial gap of the sensitive capacitor; w 1 is the distance between the vibration plate and the elastic beam; w 2 is the width of the vibrating plate, w 3 is the length of the vibrating plate, ε 0 is the dielectric constant or permittivity of air, ε 0 =8.85×10 -12 F / m; is the tensile and compressive elastic modulus, is Poisson's ratio;

[0057] It can be seen that the differential detection capacitance Δ C Torsion angle with the vibrating plate θ related, and when the torsion angle θ When it is smaller, it has better linearity;

[0058] S23.Process design;

[0059] S231. Use an adapter to adjust the height of the probe so that the probe and the upper surface of the package cover are located in the same plane, which is convenient for fixing the probe and the package cover on the same processing surface for synchronous engraving, or pasting material layers, so that the probe and the package cover surface have a coherent surface texture during processing;

[0060] S232. Alignment lines are used for positioning, and the electrode substrate and the interface circuit are aligned and installed by setting corresponding alignment lines on the electrode substrate and the interface circuit; the probe installation alignment line is set on the upper surface of the support frame, so that the probe and the package cover plate have a coherent surface texture after assembly;

[0061] S233. Use CFD software to optimize the design of components and circuits of MEMS friction sensors;

[0062] S234. Use visual precision positioning system, three-degree-of-freedom micro-manipulation alignment platform, vacuum suction head and image recognition system to assemble MEMS friction sensor;

[0063] S24. Displacement calculation;

[0064] S241. Give the typical dimensions of MEMS friction sensors;

[0065] S242. Typical load of a given MEMS friction sensor;

[0066] S243. Under the premise of not changing the flow characteristics of the aircraft model surface, determine the maximum width of the annular gap between the probe and the package cover through ANSYS simulation calculation; determine the maximum width of the annular gap between the probe and the package cover through ANSYS simulation calculation under the typical load of the test. x The maximum displacement of the axis and the capacitance gap of the sensitive capacitance element are determined at the same time h 0.

[0067] The MEMS friction sensor for measuring the friction of a rough surface of the present invention is decomposed into a floating element, a silicon microstructure, an electrode substrate, an interface circuit and a packaging tube shell, which are then processed and assembled separately; wherein the silicon microstructure is processed by a deep reactive ion etching technology of single crystal silicon material, the electrode substrate is manufactured by a Pyrex glass wet etching and metal deposition technology, the interface circuit is manufactured by a ceramic-based precision microstrip circuit technology, the floating element is processed by a duralumin material precision instrument lathe, and the packaging tube shell is processed by a duralumin material precision machinery.

[0068] The MEMS friction sensor for measuring the friction of a rough surface of the present invention adopts a special manufacturing method, and the manufacturing method includes micro-assembly equipment and a micro-assembly method; wherein the micro-assembly equipment is composed of a visual precision positioning system, a three-degree-of-freedom micro-operation alignment platform, a vacuum suction head and an image recognition system; the silicon microstructure is rigidly connected to the electrode substrate through an anodic bonding technology, and the floating element is rigidly connected to the vibration plate of the silicon microstructure by a boss positioning and epoxy resin pasting method to form a header structure of the MEMS friction sensor; the header structure adopts a manufacturing method of visual precision positioning and micro-operation alignment, and is fixed to the surface of the interface circuit by epoxy resin; the header structure and the interface circuit adopt a manufacturing method of visual precision positioning and micro-operation alignment, and are fixed in the packaging tube seat by epoxy resin to realize the assembly of the MEMS friction sensor.

[0069] The MEMS friction sensor for measuring the friction of rough surfaces adopts a three-dimensional MEMS head structure in which a floating element is flush with the surface of an aircraft model to be measured, a signal output microstructure is isolated from a wind tunnel flow field, and a plate capacitor differential detection measurement method.

[0070] The MEMS friction sensor for measuring the friction of a rough surface of the present invention adopts a rough texture surface, realizing the complex environment measurement capability of the MEMS friction sensor, with a measurement range of 0-100Pa, a resolution of 0.1Pa, and a measurement bandwidth of 0-200Hz. It has the characteristics of small size, good temperature stability, and high reliability, and can accurately measure the surface friction resistance of complex aerodynamic shapes. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 It is a schematic diagram of the overall structure of the MEMS friction sensor for measuring the friction of a rough surface according to the present invention;

[0072] Figure 2 An exploded view of the overall structure of the MEMS friction sensor for measuring the friction of a rough surface according to the present invention;

[0073] Figure 3 It is a schematic diagram of the structure of the floating element in the MEMS friction sensor for measuring the friction of a rough surface of the present invention;

[0074] Figure 4 A schematic diagram of a silicon microstructure in a MEMS friction sensor for measuring friction on a rough surface according to the present invention;

[0075] Figure 5 This is a schematic diagram of the electrode substrate structure in the MEMS friction sensor for measuring the friction of a rough surface according to the present invention;

[0076] Figure 6 A schematic diagram of a "silicon-glass" bonding structure established between a silicon microstructure and an electrode substrate in a MEMS friction sensor for measuring friction on a rough surface of the present invention;

[0077] Figure 7 It is a schematic diagram of the structure of the meter head in the MEMS friction sensor for measuring the friction of a rough surface of the present invention;

[0078] Figure 8 It is an exploded view of the installation of the adapter, the floating element and the packaging tube shell in the MEMS friction sensor for measuring the friction of a rough surface of the present invention;

[0079] Fig. 9 A schematic diagram of a circuit in a MEMS friction sensor for measuring friction on a rough surface according to the present invention;

[0080] Fig.10 The figure is a schematic diagram of the working principle of the MEMS friction sensor for measuring the friction of a rough surface according to the present invention.

[0081] In the figure, 1. packaging cover; 2. floating element; 3. silicon microstructure; 4. electrode substrate; 5. interface circuit; 6. packaging tube seat; 7. solder pad; 8. packaging positioning boss; 9. probe; 10. support rod; 11. positioning step; 12. support frame; 13. elastic beam; 14. vibration plate; 15. lead electrode; 16. glass boss; 17. gold electrode; 18. sensitive capacitor element; 19. adapter; 20. silicon capacitor installation alignment line; 21. floating element installation alignment line. DETAILED DESCRIPTION

[0082] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0083] Embodiment 1:

[0084] The structure of the MEMS friction sensor of the embodiment is as follows Figure 1 , Figure 2 As shown, it is decomposed into a package cover plate 1, a floating element 2, a silicon microstructure 3, an electrode substrate 4, an interface circuit 5 and a package base 6, which are processed separately and then assembled. The package base 6 includes a package positioning boss 8. Among them, the floating element 2 includes a probe 9, a support rod 10 and a positioning step 11, as shown in FIG. Figure 3 As shown; the silicon microstructure 3 comprises a support frame 12, a torsion beam 13 and a vibration plate 14, as Figure 4 The electrode substrate 4 comprises a lead electrode 15, a glass boss 16 and a gold electrode 17, as shown Figure 5 The vibrating plate 14 of the silicon microstructure 3 and the gold electrode 17 of the electrode substrate 4 constitute a differential sensitive capacitor element 18 to achieve differential capacitance detection, such as Figure 6 The floating element 2, the silicon microstructure 3 and the electrode substrate 4 together constitute the header structure of the MEMS friction sensor, as shown in FIG. Figure 7 shown.

[0085] Working principle of MEMS friction sensor: Probe 9 sensing and surface area A Proportional to and perpendicular to x Frictional resistance in the axial direction f s , the support rod 10 will reduce the friction resistance f s Convert to friction torque T s , friction torque T s The elastic beam 13 fixed at both ends is torsionally deformed, and the vibration pole plate 14 rigidly connected to the elastic beam 13 is torsionally deformed. y Twist angle of shaft θ , the sensitive capacitance on both sides of the elastic beam 13 C 1 and sensitive capacitor C 2 Produce certain changes, such as Figure 8By differentially calculating the change Δ of the sensitive capacitance on both sides of the elastic beam 13 C , and then calculate the friction resistance sensed by the probe 9 f s .

[0086] The real material is numerically modeled, and a suitable rough texture is designed. The probe 9 and the package cover plate 1 are fixed on the same processing surface by using the adapter 19 for integral engraving, which can ensure the consistency of the engraved texture of the probe 9 and the package cover plate 1. Fig. 9 As shown; in order to facilitate the precise alignment and assembly of the chip, the floating element 2 and the electrode substrate 4, alignment lines I and II are engraved on the upper surface of the electrode substrate 4, and the layout of the components and the on-board fixed resistors, capacitors and bonding wires are optimized by CFD software, as shown in FIG. Fig.10 As shown;

[0087] The surface friction resistance sensed by the probe 9 is proportional to the area. f s It can be expressed as:

[0088] ;

[0089] in, A is the area of ​​probe 9, is the friction resistance per unit area;

[0090] The friction resistance torque transmitted to the elastic beam 13 T s :

[0091] ;

[0092] in, h 2 is the distance between the upper surface of the probe 9 and the center line of the torsion axis;

[0093] Torsional elastic coefficient of elastic beam 13 K :

[0094] ;

[0095] in, G is the shear elastic modulus of single crystal silicon; I p is the polar moment of inertia of the cross section of the elastic beam 13, , w , h , l 1 are the width, thickness and length of the elastic beam 13, respectively, β is the torsion coefficient of the rectangular section, ;

[0096] The vibration plate 14 has a friction resistance moment T s A certain torsion angle is generated under the action θ :

[0097] ;

[0098] It can be seen that the torsion angle θ With friction resistance f s is proportional to;

[0099] The vibration pole plate 14 generates a torsion angle θ The differential sensing capacitance Δ C :

[0100] ;

[0101] in, h 0 is the initial gap of the sensitive capacitor; w 1 is the distance between the vibration plate 14 and the elastic beam 13; w 2 is the width of the vibration plate 14, w 3 is the length of the vibrating plate, ε 0 is the dielectric constant or permittivity of air, ε 0 =8.85×10 -12 F / m; is the tensile and compressive elastic modulus, is Poisson's ratio.

[0102] Equation (4) shows that the angular displacement θ With friction resistance f s is proportional to; (5) shows that the differential detection capacitance Δ C The angle between the vibration plate 14 θ Related, and when θ The smaller the value, the better the linearity. The typical size of the elastic beam 13 in this embodiment is 2000 microns × 130 microns × 500 microns, the area of ​​the capacitor plate 14 is 2050 microns × 4000 microns, and the initial gap of the sensitive capacitor element 18 is h0 is 10 microns. The range of the MEMS friction sensor is 0~100Pa, and the resolution is 0.5Pa. The resolution of the corresponding differential detection capacitor is about 10fF (currently, the detection resolution under weak capacitance stable conditions is 5fF). When the friction resistance per unit area to be measured is 100Pa, the ANSYS simulation results show that the maximum normal displacement of the vibration plate 14 is about 2.3 microns; when a normal load of 2000Pa is applied at the same time, the ANSYS simulation results show that the overall normal movement of the vibration plate 14 is about 0.2 microns, which is much smaller than the initial capacitance gap of the sensitive capacitor element 18. h 0 and the normal displacement of the vibrating plate 14 caused by friction resistance have little effect on the differential detection capacitance.

[0103] In order not to change the flow characteristics of the airflow on the surface of the aircraft model, the upper surface of the probe 9 must be flush with the surface of the aircraft model. This embodiment is implemented by packaging the tube shell, and the upper surface of the packaging cover plate 1 is flush with the surface of the aircraft model and the upper surface of the probe 9. x The friction resistance in the axial direction is transmitted to the elastic beam 13 through the support rod 10, and causes the probe 9 to generate a rotation y The torsion of the shaft ( Fig.10 ), a certain movement gap must be maintained between the probe 9 and the package cover plate 1 ( Figure 1 ). ANSYS simulation results show that the probe 9 x The maximum movement displacement of the axis is about 10 microns; CFD simulation results show that when the annular gap between the probe 9 and the package cover plate 1 is no more than 150 microns, the flow characteristics of the aircraft model surface will not be changed. Therefore, the gap between the probe 9 and the package cover plate 1 is designed to be 100 microns, which is achieved through visual alignment technology.

[0104] This embodiment innovates in the rough texture surface design of the MEMS friction sensor for measuring rough textured surfaces, and innovates in the process methods for processing and assembling the MEMS friction sensor, thereby improving the processing and assembly accuracy of the MEMS friction sensor, and further improving its accuracy in measuring the surface friction resistance of the aircraft model in the hypersonic wind tunnel flow field, and realizing the complex surface measurement capability of the MEMS friction sensor, with a measurement range of 0~100Pa, a resolution of 0.5Pa, and a measurement bandwidth of 0~200Hz. It has the characteristics of small size, good temperature stability, and high reliability, and can measure the surface friction resistance of the complex surface of the aircraft model in the hypersonic flow field.

[0105] The above embodiments only express typical implementations of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention's patent shall be subject to the attached claims.

[0106] The above embodiments only express typical implementations of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention's patent shall be subject to the attached claims.

Claims

1. A MEMS friction sensor for measuring friction on a rough surface, characterized in that: The MEMS friction sensor comprises a packaging cover plate (1), a meter head structure, an interface circuit (5) and a packaging tube shell; The package tube shell comprises a package cover plate (1) and a package tube seat (6) stacked in sequence from top to bottom; the package tube seat (6) is cylindrical and has a groove on its surface; a package positioning boss (8) is provided on the upper surface of the package tube seat (6) along the periphery of the groove; a circular adapter (19) is mounted on the package positioning boss (8); a stepped circular tube-shaped package cover plate (1) is mounted outside the adapter (19); the bottom surface diameter of the package cover plate (1) is equal to the top surface diameter of the package tube seat (6), and the top surface diameter of the package cover plate (1) is smaller than the top surface diameter of the package tube seat (6); a meter head structure and an interface circuit (5) are mounted in the stepped cylindrical central cavity of the package cover plate (1); The head structure comprises a floating element (2), a silicon microstructure (3) and an electrode substrate (4), and the head structure is used to sense the friction resistance of the aircraft model surface and convert it into a differential capacitance signal; the floating element (2) comprises a centrally symmetrical disc-shaped probe (9), a support rod (10) and a positioning step (11) connected in sequence from top to bottom; the probe (9) and the packaging cover plate (1) are flush with the surface of the aircraft model, the surfaces of the probe (9) and the packaging cover plate (1) have a continuous surface texture, and there is an annular gap between the probe (9) and the packaging cover plate (1); the probe (9) senses the friction resistance of the aircraft model surface, and the support rod (10) converts the friction resistance into a friction resistance torque and transmits it to the silicon microstructure (3) through the positioning step (11); the positioning step (11) is used to determine the position of the floating element (2) in the vertical direction of the silicon microstructure (3); The silicon microstructure (3) comprises an elastic beam (13), a vibration pole plate (14) and a support frame (12); the support frame (12) is a square flat plate, and continuous cutting is performed on the support frame (12) to obtain a Chinese-character-shaped component at the center; the parts extending from the left and right ends of the Chinese-character-shaped component are left-right symmetrical elastic beams (13), the elastic beams (13) are fixed beams at both ends, the torsional stiffness of the elastic beams (13) is less than the normal stiffness, and mainly torsional deformation occurs when inducing friction resistance; the middle part of the Chinese-character-shaped component is a vibration pole plate (14) that is symmetrical in height relative to the elastic beam (13); a through hole corresponding to the positioning step (11) is provided at the center of the vibration pole plate (14); a probe (9) installation alignment line is provided on the upper surface of the support frame (12); the support frame (12) supports the vibration pole plate (14) and the floating element (2) through the elastic beam (13); The electrode substrate (4) comprises a lead electrode (15), a glass boss (16) and a gold electrode (17); the upper surface of the electrode substrate (4) is provided with two gold electrodes (17) symmetrically arranged in the upper and lower directions corresponding to the vibration pole plate (14); each gold electrode (17) extends to the left and right respectively, and the extended part forms the lead electrode (15); the glass boss (16) is arranged in the remaining area of ​​the upper surface of the electrode substrate (4); the gold electrode (17) and the vibration pole plate (14) of the silicon microstructure (3) together constitute a sensitive capacitor element (18); the glass boss (16) and the support frame (12) of the silicon microstructure (3) are anodic bonded, and the height of the glass boss (16) is equal to the capacitance gap constituting the sensitive capacitor element (18). h 0; the upper surface of the electrode substrate (4) is engraved with alignment lines I and II; The interface circuit (5) comprises a circuit substrate, which is placed in a groove of a package tube seat (6). A plurality of electronic components and a soldering pad (7) are arranged on the circuit substrate, and the soldering pad (7) is used to connect to the lead electrode (15) of the electrode substrate (4). The upper surface of the circuit substrate is engraved with a silicon capacitor installation alignment line (20) corresponding to the alignment line I of the electrode substrate (4), and a floating element installation alignment line (21) corresponding to the alignment line II of the electrode substrate (4). One processing method for forming the continuous surface texture on the surfaces of the probe (9) and the package cover plate (1) is to use an adapter (19) to fix the probe (9) and the package cover plate (1) on the same processing surface for synchronous engraving. Another processing method is to adhere a material layer consistent with the surface material of the aircraft model on the surfaces of the probe (9) and the package cover plate (1); The alignment line I is aligned with the silicon capacitor installation alignment line (20), and the alignment line II is aligned with the floating element installation alignment line (21), so as to ensure that the surface textures of the probe (9) and the packaging cover plate (1) are continuous after installation.

2. The MEMS friction sensor for measuring friction on a rough surface according to claim 1, characterized in that: The silicon microstructure (3) is processed by deep reactive ion etching technology of single crystal silicon material; the electrode substrate (4) is manufactured by Pyrex glass wet etching and metal deposition technology; the interface circuit (5) is manufactured by ceramic-based precision microstrip circuit technology; the floating element (2) is processed by a hard aluminum material precision instrument lathe, and the packaging tube shell is processed by hard aluminum material precision machinery; Ceramic-based precision microstrip circuit technology uses a ceramic-based precision circuit substrate and is manufactured using a precision ceramic microstrip circuit process. The precision ceramic microstrip circuit process includes substrate cutting, double-sided metal sputtering, electroplating metal thickening and photolithography etching.

3. The MEMS friction sensor for measuring friction on a rough surface according to claim 1, characterized in that: The interface circuit (5) is provided with a plurality of electronic components including a capacitance detection chip AD7747, a single-chip microcomputer C8051F411, an FPC seat and a peripheral circuit; the capacitance detection chip AD7747 converts a differential capacitance signal into a digital signal; the single-chip microcomputer C8051F411 controls the working state of the AD7747 and receives the capacitance value collected in real time by the AD7747, and sends the capacitance value to a host computer for subsequent processing; the host computer is programmed using Labwindows CVI; the data acquisition update rate of the interface circuit (5) is 20 Hz, and the capacitance resolution is 4.99×10 ~4 pF.

4. A method for manufacturing a MEMS friction sensor for measuring friction on a rough surface, which is used to manufacture the MEMS friction sensor for measuring friction on a rough surface as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: S11. Based on the design indicators of the MEMS friction sensor, use CFD software to optimize the design of each component and circuit of the MEMS friction sensor; S12. Processing the components of the MEMS friction sensor separately; S13. Assembling the silicon microstructure (3) and the electrode substrate (4); Under a precision visual device, the interface circuit (5) is fixed at position I on a three-degree-of-freedom micro-operation alignment platform; the alignment line I of the electrode substrate (4) is aligned with the silicon capacitor installation alignment line (20) on the interface circuit (5), the alignment line II of the electrode substrate (4) is aligned with the floating element installation alignment line (21) on the interface circuit (5), and the electrode substrate (4) is fixed to the interface circuit (5) using epoxy resin; the silicon microstructure (3) is then aligned with the electrode substrate (4), and the silicon microstructure (3) is fixed to the electrode substrate (4) using epoxy resin; S14. Assembling the floating element (2); Under a precision visual device, the positioning step (11) of the floating element (2) is inserted into the through hole of the vibration plate (14) of the silicon microstructure (3), and then the texture direction of the probe (9) is rotated to the probe (9) installation alignment line on the upper surface of the support frame (12) of the silicon microstructure (3), and finally the positioning step (11) is fixed by gluing with epoxy resin to obtain an assembly; S15. Fixed package tube holder (6); Fixing the package tube holder (6) at position II of the three-degree-of-freedom micro-operation alignment platform; S16. Identify the installation position of the package cover (1); The packaging cover plate (1) is mounted on the packaging tube seat (6), ensuring that the packaging cover plate (1) is mounted on the side of the packaging tube seat (6) without any steps; using a visual precision positioning system of a precision visual device to take a picture of the packaging cover plate (1), and identifying the position of the circular hole on the surface of the packaging cover plate (1) through an image recognition system; S17. Assemble the components; Remove the package cover plate (1), place the interface circuit (5) of the assembly into the groove of the package tube seat (6), clamp the assembly with a vacuum suction head, use the visual precision positioning system and the vacuum suction head to move the assembly in the groove, align the probe (9) with the circular hole on the surface of the package cover plate (1), and fix the assembly on the package tube seat (6) with epoxy resin; S18. Welding circuit; spot welding the lead wire between the lead electrode (15) and the pad (7); S19. Assembling the packaging cover plate (1); The adapter (19) is mounted on the package positioning boss (8) of the package tube seat (6), and then the package cover plate (1) is mounted on the adapter (19), and the package cover plate (1) is ensured to be coaxial with the probe (9), thereby completing the assembly of the MEMS friction sensor.

5. A method for designing a MEMS friction sensor for measuring friction on a rough surface, which is used to design a MEMS friction sensor for measuring friction on a rough surface as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: S21. Mechanical analysis; Probe (9) sensing and surface area A Proportional to and perpendicular to x Frictional resistance in the axial direction f s , the support rod (10) reduces the friction resistance f s Converted into friction torque T s , friction resistance torque T s The elastic beam (13) fixedly supported at both ends is subjected to torsional deformation, and the vibration pole plate (14) rigidly connected to the elastic beam (13) is subjected to torsional deformation. y Twist angle of shaft θ , the sensitive capacitance on both sides of the elastic beam (13) C 1 and sensitive capacitor C 2 changes; by differential calculation of the sensitive capacitance on both sides of the elastic beam (13) C 1 and sensitive capacitor C 2 The change of Δ C , and then calculate the friction resistance sensed by the probe (9) f s ; S22. Mechanical calculation; The surface friction resistance sensed by the probe (9) is proportional to the area. f s It can be expressed as: ； in, A is the surface area of ​​the probe (9), is the friction resistance per unit area; The friction resistance torque transmitted to the elastic beam (13) T s : ； in, h 2 is the distance between the upper surface of the probe (9) and the center line of the torsion axis; Torsional elastic coefficient of the elastic beam (13) K : ； in, G is the shear elastic modulus of single crystal silicon; I p is the polar moment of inertia of the cross section of the elastic beam (13), , w , h , l 1 are the width, thickness and length of the elastic beam (13), β is the torsion coefficient of the rectangular section, ； The friction resistance torque of the vibrating plate (14) T s A certain torsion angle is generated under the action θ : ； It can be seen that the torsion angle θ With friction resistance f s is proportional to; The vibrating pole plate (14) generates a torsion angle θ The differential sensing capacitance Δ C : ； in, h 0 is the initial gap of the sensitive capacitor; w 1 is the distance between the vibration pole plate (14) and the elastic beam (13); w 2 is the width of the vibration plate (14), w 3 is the length of the vibrating plate, ε 0 is the dielectric constant or permittivity of air, ε 0 =8.85×10 -12 F / m; is the tensile and compressive elastic modulus, is Poisson’s ratio; It can be seen that the differential detection capacitance Δ C The torsion angle with the vibration pole plate (14) θ related, and when the torsion angle θ When it is smaller, it has better linearity; S23.Process design; S231. The height of the probe (9) is adjusted by using an adapter (19) so that the upper surfaces of the probe (9) and the package cover plate (1) are located in the same plane, so that the probe (9) and the package cover plate (1) are conveniently fixed on the same processing surface for synchronous engraving, or for pasting material layers, so that the surfaces of the probe (9) and the package cover plate (1) have a continuous surface texture during processing; S232. Alignment lines are used for positioning, and corresponding alignment lines are provided on the electrode substrate (4) and the interface circuit (5) to achieve alignment and installation of the electrode substrate (4) and the interface circuit (5); alignment lines for installing the probe (9) are provided on the upper surface of the support frame (12), so that after assembly, the probe (9) and the packaging cover plate (1) have a continuous surface texture; S233. Use CFD software to optimize the design of components and circuits of MEMS friction sensors; S234. Use visual precision positioning system, three-degree-of-freedom micro-operation alignment platform, vacuum suction head and image recognition system to assemble MEMS friction sensor; S24. Displacement calculation; S241. Give the typical dimensions of MEMS friction sensors; S242. Typical load of a given MEMS friction sensor; S243. Under the premise of not changing the flow characteristics of the aircraft model surface, the maximum width of the annular gap between the probe (9) and the package cover (1) is determined by ANSYS simulation calculation; under the typical load of the calibration, the maximum width of the annular gap between the probe (9) and the package cover (1) is determined by ANSYS simulation calculation. x The maximum displacement of the shaft is determined by the capacitive gap of the sensitive capacitive element (18) h 0.

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