Conformal MEMS friction resistance sensor for measuring surface friction resistance of cone model and assembling method of conformal MEMS friction resistance sensor

Abstract

The invention belongs to the technical field of micro electro mechanical systems, and discloses a conformal MEMS friction sensor for measuring friction on the surface of a cone model and an assembling method of the conformal MEMS friction sensor. The conformal MEMS friction resistance sensor comprises a packaging tube shell, a meter head structure and an interface circuit, the packaging tube shell protects the meter head structure and the interface circuit through the packaging cover plate and the packaging tube base which are locked up and down. The conformal MEMS friction resistance sensor is perpendicular to the generatrix of the cone model and is installed on the surface of the cone model, the surface friction resistance in the direction parallel to the generatrix is directly measured, and friction resistance measurement of automatically deducting differential pressure resistance is carried out. The assembling method comprises the steps of assembling the silicon-glass microstructure and the interface circuit, assembling the floating element and assembling the packaging tube shell. The conformal MEMS friction resistance sensor for measuring the friction resistance on the surface of the cone model and the assembly method have the characteristics of small size, good temperature stability, high reliability and the like, and the friction resistance on the surface of the cone model can be accurately measured.

Description

Technical Field

[0001] The invention belongs to the technical field of micro-electromechanical systems, and in particular relates to a conformal MEMS friction sensor for measuring friction on a cone model surface and an assembling 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. Due to the limitations of sensitivity, temperature, volume and cost, it is 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 the field of 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] Since many applications require surface friction resistance testing in hypersonic wind tunnel flow fields, the current 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 with 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. A related article [Fabrication, calibration and proof experiments in hypersonic wind tunnel for a novel MEMS skin friction sensor, Microsystem Technologies, vol.23, No.8, 2017 [J].] was published based on this research.

[0006] In 2022, the China Patent Literature Library disclosed the invention of the inventor team, named as a high-frequency response and 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] In 2023, the China Patent Literature Library disclosed the invention of the inventor team, entitled MEMS friction sensor for measuring friction on rough surfaces and its manufacturing and design method (ZL202311226952.0). The MEMS friction sensor has 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. It can accurately measure the surface friction resistance of complex aerodynamic shapes and is suitable for hypersonic flow fields.

[0008] With the rapid development of hypersonic technology, the aerodynamic shape and aerodynamic structure design of aircraft in engineering are becoming increasingly complex. The surface to be measured on the aircraft is generally no longer a simple smooth plane, but a profiled surface with certain curvature characteristics. The measurement surfaces of the aforementioned MEMS friction sensors are all smooth planes, which cannot meet the demand for accurate measurement of friction on the aircraft surface. In hypersonic wind tunnel test research, the cone model is another typical profiled surface test research object different from the flat plate model. It is necessary to use the cone model to carry out friction measurement test research on conformal surfaces. In the design of aircraft, there are strict requirements for the conformal adaptability of friction sensors and aircraft surfaces, and not all sensors can meet this requirement. The MEMS friction sensor (ZL201418003582.X, ZL202210154250.5, ZL202311226952.0) designed by the inventor's team adopts the characteristics of mesoscopic three-dimensional header structure decomposition processing and vision-based alignment and high-precision micro-assembly process, which makes the conformal processing of the sensor probe and the upper surface of the packaging cover feasible, and has the potential to be conformal with the wall of the cone model.

[0009] Currently, there is an urgent need to develop a conformal MEMS friction sensor and assembly method for measuring friction on the surface of a cone model. Summary of the invention

[0010] One technical problem to be solved by the present invention is to provide a conformal MEMS friction sensor for measuring the friction resistance of a cone model surface. Another technical problem to be solved by the present invention is to provide an assembly method for a conformal MEMS friction sensor for measuring the friction resistance of a cone model surface, so as to conduct experimental research on the measurement of friction resistance of a cone model surface in a hypersonic wind tunnel.

[0011] The conformal MEMS friction sensor for measuring the friction of the cone model surface of the present invention comprises a packaging tube shell, a meter head structure and an interface circuit; The package tube shell comprises a package cover plate and a package tube seat stacked in sequence from top to bottom; wherein a groove is arranged at the bottom of the package cover plate, a package positioning boss is arranged on the upper surface of the package base, and the package cover plate and the package tube seat are connected and locked through the groove and the package positioning boss; The meter head structure is a sensitive element of the common MEMS friction sensor, which converts the friction resistance measured by the common MEMS friction sensor into a capacitance signal; the meter head structure includes a floating element, a silicon microstructure and an electrode substrate connected in sequence from top to bottom; the silicon microstructure and the electrode substrate are anodically bonded to form a silicon-glass microstructure; The floating element comprises a probe, a support rod and a positioning step connected in sequence from top to bottom; wherein the upper surface of the probe and the upper surface of the package cover are flush with the conical model, the surfaces of the probe and the package cover are conformal, and there is an annular gap between the probe and the package cover; the positioning step is embedded in the positioning hole of the silicon microstructure to ensure that the floating element is vertically connected to the silicon microstructure; when the probe is subjected to friction resistance, the probe is deflected by force, and the support rod converts the friction resistance into friction resistance torque and transmits it to the silicon microstructure through the positioning step; The silicon microstructure comprises an elastic beam, a vibration pole plate and a support frame, wherein the silicon microstructure is cut from a rectangular parallelepiped, the vibration pole plate is at the center of the silicon microstructure, the elastic beam is a fixed support beam at both ends, and is located on both sides of the vibration pole plate; the support frame is located around the vibration pole plate and the support frame, and the vibration pole plate and the floating element are supported by the elastic beam; when the floating element transmits the friction torque through the support rod, the elastic beam is subjected to torsion deformation, driving the vibration pole plate to occur y Deflection of direction; The electrode substrate comprises lead electrodes, glass bosses and two Au electrodes, wherein the lead electrodes are divided into two groups, which are located on both sides of the electrode substrate. Each group of lead electrodes extends left and right and converges into two Au electrodes in the middle. The lead electrodes are connected to the interface circuit leads. The glass bosses are arranged in the remaining area on the upper surface of the electrode substrate. The Au electrodes and the vibration plates constitute the upper and lower plates of the sensitive capacitor element. The glass bosses and the support frame are anodic bonded. The upper and lower gaps constitute the capacitor gap of the sensitive capacitor element. h 0 ; When the vibrating plate is deflected by force, the capacitor plate of the sensitive capacitor element is deflected, and the capacitance value of the sensitive capacitor element changes; The interface circuit is a ceramic circuit substrate, which is placed in a groove of a package tube seat. A high-frequency micro-capacitance detection chip Pcap01, a single-chip microcomputer STM32F411CEU6, an FPC seat, a variety of capacitance elements, resistance elements and a plurality of pads are arranged on the circuit substrate. The pads are connected to lead electrode leads, the FPC seat is connected to the interface circuit and an acquisition computer, the micro-capacitance detection chip converts a differential capacitance signal into a digital signal, the single-chip microcomputer controls the working state of the micro-capacitance detection chip, receives the converted digital signal and sends it to the acquisition computer, and the sampling rate of the interface circuit is 100 Hz.

[0012] The assembly method of the conformal MEMS friction sensor for measuring the friction of the cone model surface of the present invention comprises the following steps: S21. Install the conformal MEMS friction sensor on the surface of the cone model perpendicular to the generatrix of the cone model; the floating element of the sensor is symmetrical along the neutral plane where the elastic beam is located, and the left and right sides have the same shape and size; S22. When the probe diameter is less than or equal to 5 mm, the pressure distribution on both sides of the neutral surface of the elastic beam is the same, and the surface friction resistance in the direction parallel to the generatrix is ​​directly measured, excluding the pressure difference resistance caused by the pressure imbalance along the airflow direction, so as to realize the friction resistance measurement with automatic deduction of the pressure difference resistance; S23. When the diameter of the probe is greater than 5mm, the pressure distribution on both sides of the neutral plane of the elastic beam is also the same; when no wind tunnel test is conducted, the floating element is in a deflected state, the elastic beam is in a torsion state, and the interface circuit outputs the initial value of the capacitance signal; when the wind tunnel test is conducted, the deflection angle of the floating element increases, the elastic beam also increases its torsion, and the interface circuit outputs the test value of the capacitance signal; the difference between the initial value of the capacitance signal and the test value of the capacitance signal is calculated to offset the normal force of the sensitive capacitance elements on both sides of the floating element in the static and blowing states, and the change in capacitance in the test state is obtained, and the surface friction resistance of the floating element is calculated through the performance parameters of the sensor and the force-sensitive mechanism of the head structure of the common MEMS friction sensor.

[0013] Furthermore, the force-sensitive mechanism calculation process includes the following steps: S31. Perform mechanical analysis; The probe surface of the floating element is flush with the wall to be measured as the measuring surface, and the probe sensing is proportional to the force area A of the probe and is perpendicular to Frictional resistance in the axial direction , the support rod will reduce the friction resistance Convert to friction torque , friction torque The elastic beam fixed at both ends will produce torsional deformation, and the vibrating pole plate rigidly connected to the elastic beam will produce torsional deformation. Twist angle of shaft , the capacitance value of the sensitive capacitor element and Produce changes; calculate the change in sensitive capacitance by differential , and then calculate the friction resistance sensed by the sensor ; S32. Perform mechanical calculations; Frictional resistance sensed by the probe : ; Where A is the force-bearing area of ​​the floating element; It is the friction resistance sensed by the probe per unit area; Friction torque transmitted to the elastic beam through the support rod : ; in, is the distance between the upper surface of the probe and the center line of the torsion axis; Torsional elastic coefficient of elastic beam : ; in, is the shear elastic modulus of single crystal silicon; is the cross-sectional polar moment of inertia of the elastic beam; is the torsion coefficient; is the height of the elastic beam; is the width of the elastic beam; is the length of the elastic beam; Friction torque of the vibrating plate Torsion angle : ; Vibrating pole plate produces torsion angle The differential sensing capacitor : ; in, is the capacitance gap of the sensitive capacitance element; , and is the structural parameter of the vibrating plate; is the dielectric constant of vacuum, ; is Young's modulus; is Poisson's ratio; When not testing, the floating element is in a deflected state, the capacitor plates of the sensitive capacitor element are displaced, and the differential detection capacitor Differential sensing capacitor During the wind tunnel test, the deflection angle of the floating element increases, the displacement of the capacitor plate of the sensitive capacitor element increases, and the capacitance difference is , substituting into formula (5), the capacitance difference caused by airflow is : ; The shear stress on the wall of the floating element caused by high-speed airflow for: ; in, is the friction coefficient, dynamic pressure .

[0014] Further, the assembly method includes the assembly of the silicon-glass microstructure and the interface circuit, the assembly of the floating element and the assembly of the package tube shell; The silicon-glass microstructure and interface circuit assembly are as follows: aligning the silicon microstructure and the electrode substrate, fixing the silicon microstructure on the electrode substrate by epoxy resin, and anodically bonding the silicon microstructure and the electrode substrate to obtain the silicon-glass microstructure; fixing the interface circuit on a fixed stage I of a precision visual alignment instrument, aligning the silicon capacitor installation alignment line of the interface circuit with the alignment line I of the electrode substrate, aligning the floating element installation alignment line of the interface circuit with the marking line of the floating element, and fixing the silicon-glass microstructure on the interface circuit by epoxy resin; spot welding the lead between the lead electrode and the pad to obtain an assembly of the silicon-glass microstructure and the interface circuit; Floating element assembly: insert the positioning step of the floating element into the through hole of the silicon microstructure, rotate the angle of the floating element so that the marking line on the probe surface and the boundary line of the elastic beam of the silicon wafer are perpendicular, and fix the positioning step in the through hole with epoxy resin to obtain the assembly of the head structure and the interface circuit; Package shell assembly: fix the package socket on the fixed table II of the precision vision alignment instrument, place the assembly of the interface circuit and the header structure in the groove of the package socket, clamp the assembly with the vacuum suction head, move the assembly to the center position, vertically install the package cover plate through the package positioning boss, align the marking lines on the surface of the package shell and the floating element to ensure the coaxiality and direction of the two, fix the position of the interface circuit with epoxy resin, lock the package shell and the package socket with screws, and complete the assembly of the common MEMS friction sensor.

[0015] Furthermore, the errors controlled by the assembly method include the coaxial error between the package tube shell and the probe and the flush error between the package tube shell and the floating element; Coaxial error: The coaxial error of the conformal MEMS friction sensor is measured by a precision visual alignment instrument. After the interface circuit is fixed with epoxy resin, the position of the interface circuit is adjusted by a vacuum suction head to ensure that the coaxial error between the package cover and the probe is controlled within ±5μm. Flush error: A reference surface that is at the same height as the center of the floating element is installed on the sensor package shell. The MEMS topography measurement system divides the conformal surface into several surface patches through adaptive image segmentation, calculates the relative position relationship between each surface patch and the reference surface, extracts several points from each surface patch, calculates the position from the point to the reference plane, marks the height with color, and ensures that the flush error Δh of the sensor is controlled within ±10μm by adding or removing metal gaskets between the package cover and the package socket.

[0016] Furthermore, the assembly method adopts deep reactive ion etching technology of single crystal silicon material to process the silicon microstructure, and the processing techniques include photolithography, cavity etching, metal sputtering and deep etching; the electrode substrate is made by Pyrex glass wet etching and metal deposition technology, and the processing techniques include cleaning, sputtering, photolithography of electrode patterns and removal of excess metal; the interface circuit is made by ceramic-based precision microstrip circuit technology, and the manufacturing process includes the design of the interface circuit, the processing of the ceramic substrate and the welding of the interface circuit; the floating element is processed by a precision instrument lathe made of duralumin material, and the packaging tube shell is processed by precision machinery made of duralumin material, and the floating element and the packaging cover plate are processed for common integration through tooling to ensure that the common parameters of the floating element and the packaging cover plate are consistent.

[0017] The conformal MEMS friction sensor and assembly method for measuring friction on the surface of a cone model of the present invention adopts a conical conformal surface to realize the conformal surface measurement capability of the MEMS friction sensor, with a measurement range of 0-100Pa, a resolution better than 0.2Pa, and a measurement bandwidth of 0-100Hz. It has the characteristics of small size, good temperature stability, high reliability, etc., and can accurately measure the friction resistance on the surface of a cone model. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the overall structure of a conformal MEMS friction sensor for measuring friction on a cone model surface of the present invention; Figure 2 An exploded view of the overall structure of a conformal MEMS friction sensor for measuring friction on a cone model surface according to the present invention; Figure 3 It is an exploded view of the header structure of the conformal MEMS friction sensor for measuring the friction of the cone model surface of the present invention; Figure 4 A schematic diagram of the structure of a floating element in a conformal MEMS friction sensor for measuring friction on a cone model surface according to the present invention; Figure 5 A schematic diagram of the silicon microstructure in a conformal MEMS friction sensor for measuring friction on a cone model surface of the present invention; Figure 6 A schematic diagram of the electrode substrate structure in a conformal MEMS friction sensor for measuring friction on a cone model surface according to the present invention; Figure 7 A schematic diagram of the silicon-glass bonding structure in a conformal MEMS friction sensor for measuring friction on a cone model surface according to the present invention; Figure 8 It is a schematic diagram of the interface circuit structure in the conformal MEMS friction sensor for measuring the friction of the cone model surface of the present invention; Fig. 9 It is a schematic diagram of the packaging tube seat structure in the conformal MEMS friction sensor for measuring the friction of the cone model surface of the present invention; Fig.10 It is a schematic diagram of conformal installation of a conformal MEMS friction sensor for measuring friction on a cone model surface of the present invention; Fig.11 It is a schematic diagram of the installation of a conformal MEMS friction sensor for measuring the friction of a cone model surface according to the present invention; Fig.12 It is a cross-sectional view of the installation of a conformal MEMS friction sensor for measuring friction on a cone model surface of the present invention; Fig.13 A schematic diagram of the working principle of the conformal MEMS friction sensor for measuring the friction of a cone model surface according to the present invention; Fig.14 It is a force analysis diagram of the conformal MEMS friction sensor for measuring the friction of the cone model surface of the present invention; Fig.15 It is a schematic diagram of the assembly of the silicon-glass microstructure and interface circuit of the conformal MEMS friction sensor for measuring the friction of the cone model surface of the present invention; Fig.16 It is a schematic diagram of assembling the floating element of the conformal MEMS friction sensor for measuring the friction of the cone model surface of the present invention; Fig.17 It is a schematic diagram of assembling the package tube shell of the conformal MEMS friction sensor for measuring the friction of the cone model surface of the present invention; Fig.18 A schematic diagram of the coaxial error of a conformal MEMS friction sensor for measuring friction on a cone model surface according to the present invention; Fig.19 A schematic diagram of the flatness error of a conformal MEMS friction sensor for measuring friction on a cone model surface according to the present invention.

[0019] In the figure, 1. package cover; 2. header structure; 3. interface circuit; 4. package tube seat; 5. floating element; 6. silicon microstructure; 7. electrode substrate; 8. silicon-glass microstructure; 9. probe; 10. support rod; 11. positioning step; 12. sensitive capacitor element; 13. support frame; 14. elastic beam; 15. vibration plate; 16. lead electrode; 17. glass boss; 18. Au electrode; 19. pad; 20. package positioning boss; 21. floating element installation alignment line; 22. silicon capacitor installation alignment line. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0021] Example: Figure 1 , Figure 2 As shown in FIG. 1 , the structure of the conformal MEMS friction sensor for measuring the friction of the cone model surface in this embodiment is decomposed into a package cover plate 1, a header structure 2, an interface circuit 3 and a package socket 4. Each component is processed with high precision and then micro-assembled and integrated; Figure 3 As shown, the header structure 2 includes a floating element 5, a silicon microstructure 6 and an electrode substrate 7. Figure 4 As shown, the floating element 5 includes a probe 9, a support rod 10 and a positioning step 11. Figure 5 As shown, the silicon microstructure 6 includes a support frame 13, an elastic beam 14 and a vibration plate 15. Figure 6 As shown, the electrode substrate 7 includes a lead electrode 16, a glass boss 17 and an Au electrode 18. Figure 7 As shown, the silicon microstructure 6 and the electrode substrate 7 are anodically bonded to obtain a silicon-glass microstructure 8, and the vibration plate 15 of the silicon microstructure 6 and the Au electrode 18 of the electrode substrate 7 constitute a differential sensitive capacitor element 12 to achieve differential capacitance detection. Figure 8 As shown, the interface circuit 3 is a ceramic circuit substrate, on which a high-frequency micro-capacitance detection chip Pcap01, a single-chip microcomputer STM32F411CEU6, an FPC seat, resistor elements, various capacitor elements and pads 19 are arranged.

[0022] The package tube shell comprises a package cover plate 1 and a package tube base 4 stacked in sequence from top to bottom; wherein a groove is arranged at the bottom of the package cover plate 1, and a package positioning boss 20 is arranged on the upper surface of the package base, such as Fig. 9 As shown, the package cover plate 1 and the package tube seat 4 are connected and locked via the groove and the package positioning boss 20; The meter head structure 2 is a sensitive element of the common MEMS friction sensor, which converts the friction resistance measured by the common MEMS friction sensor into a capacitance signal; the meter head structure 2 includes a floating element 5, a silicon microstructure 6 and an electrode substrate 7 connected in sequence from top to bottom; the silicon microstructure 6 and the electrode substrate 7 are anodically bonded to form a silicon-glass microstructure 8; The floating element 5 comprises a probe 9, a support rod 10 and a positioning step 11 connected in sequence from top to bottom; wherein the upper surface of the probe 9 and the upper surface of the package cover plate 1 are flush with the cone model, the surfaces of the probe 9 and the package cover plate 1 are conformal, and there is an annular gap between the probe 9 and the package cover plate 1; the positioning step 11 is embedded in the positioning hole of the silicon microstructure 6 to ensure that the floating element 5 is vertically connected to the silicon microstructure 6; when the probe 9 is subjected to friction resistance, the probe 9 is deflected by force, and the support rod 10 converts the friction resistance into friction resistance torque and transmits it to the silicon microstructure 6 through the positioning step 11; The silicon microstructure 6 includes an elastic beam 14, a vibration pole plate 15 and a support frame 13, wherein the silicon microstructure 6 is cut from a rectangular parallelepiped, the vibration pole plate 15 is at the center of the silicon microstructure 6, the elastic beam 14 is a fixed support beam at both ends, and is located on both sides of the vibration pole plate 15; the support frame 13 is located around the vibration pole plate 15 and the support frame 13, and the vibration pole plate 15 and the floating element 5 are supported by the elastic beam 14; when the floating element 5 transmits the friction torque through the support rod 10, the elastic beam 14 is subjected to force to twist and deform, driving the vibration pole plate 15 to occur y Deflection of direction; The electrode substrate 7 includes a lead electrode 16, a glass boss 17 and two Au electrodes 18, wherein the lead electrode 16 is divided into two groups, located on both sides of the electrode substrate 7, each group of lead electrodes 16 extends left and right and converges in the middle to form two Au electrodes 18, the lead electrode 16 is connected to the interface circuit 3 by a lead wire, and the glass boss 17 is arranged in the remaining area on the upper surface of the electrode substrate 7; the Au electrode 18 and the vibration plate 15 constitute the upper and lower plates of the sensitive capacitor element 12, the glass boss 17 and the support frame 13 are anodic bonded, and the upper and lower gaps constitute the capacitance gap of the sensitive capacitor element 12 h 0 ; When the vibrating plate 15 is deflected by force, the capacitor plate of the sensitive capacitor element 12 is deflected, and the capacitance value of the sensitive capacitor element 12 changes; The interface circuit 3 is a ceramic board circuit substrate, which is placed in the groove of the packaging tube seat 4. A high-frequency micro-capacitance detection chip Pcap01, a single-chip microcomputer STM32F411CEU6, an FPC seat, a variety of capacitive elements, resistive elements and a number of pads 19 are arranged on the circuit substrate. The pads 19 are connected to the lead electrodes 16 by leads. The FPC seat connects the interface circuit 3 and the acquisition computer. The micro-capacitance detection chip converts the differential capacitance signal into a digital signal. The single-chip microcomputer controls the working state of the micro-capacitance detection chip and receives the converted digital signal and sends it to the acquisition computer. The sampling rate of the interface circuit 3 is 100Hz.

[0023] The assembly method of the conformal MEMS friction sensor for measuring the friction of the cone model surface of this embodiment is based on the conformal MEMS friction sensor head 9 surface being parallel to the generatrix of the cone model, and the support rod 10 of the floating element 5 being conformally installed perpendicular to the generatrix of the cone model, such as Fig.10 As shown, the conformal MEMS friction sensor is installed on the surface of the cone model perpendicular to the generatrix of the cone model; The assembly method uses the sensor floating element 5 to be symmetrical along the neutral plane where the elastic beam 14 is located, and the left and right sides have the same shape and size; when the diameter of the probe 9 is less than or equal to 5mm, the pressure change along the flow direction is not considered, and the pressure distribution of the probe 9 along the neutral plane on both sides of the elastic beam 14 is the same, and the surface friction resistance in the direction parallel to the generatrix is ​​directly measured, and the pressure difference resistance caused by the pressure imbalance along the flow direction of the airflow is not included, so that the friction resistance measurement with the pressure difference resistance automatically deducted is realized; At the same time, the floating element 5 is symmetrical along the neutral plane where the elastic beam 14 is located, and the interchangeable direction of the conformal MEMS friction sensor does not affect the measurement result when measuring the surface of the cone model; the support rod 10 of the floating element 5 is perpendicular to the generatrix of the cone model, and the surface of the probe 9 is parallel to the generatrix of the cone model. The conformal structure shape and size at any position in the direction of the generatrix of the cone model are consistent, such as Fig.11 , Fig.12 As shown in the figure, the conformal MEMS friction sensor can be installed at any position along the generatrix of the cone model without affecting the measurement results. The conformal MEMS friction sensor is installed on the surface of the cone model perpendicular to the normal of the cone model, and the areas on the left and right sides of the center line of the floating element 5 are the same; when the wind tunnel test is not carried out, the floating element 5 is in a deflected state, the elastic beam 14 is in a torsion state, and the interface circuit 3 outputs the initial value of the capacitance signal; when the wind tunnel test is carried out, the deflection angle of the floating element 5 is increased, the torsion of the elastic beam 14 is increased, and the interface circuit 3 outputs the test value of the capacitance signal; the difference between the initial value of the capacitance signal and the test value of the capacitance signal is calculated to offset the normal force of the sensitive capacitance elements 12 on both sides of the floating element 5 in the static and blowing states, and the change in the capacitance in the test state is obtained, and the surface friction resistance of the floating element 5 is calculated through the performance parameters of the sensor and the force-sensitive mechanism of the header structure 2 of the conformal MEMS friction sensor.

[0024] Furthermore, the force-sensitive mechanism calculation process includes the following steps: S31. Perform mechanical analysis; The probe 9 surface of the floating element 5 is used as a measuring surface and is flush with the wall to be measured. The probe 9 senses a force area A proportional to the probe 9 and perpendicular to the Frictional resistance in the axial direction , the support rod 10 will reduce the friction resistance Convert to friction torque , friction torque The elastic beam 14 fixed at both ends is torsionally deformed, and the vibration pole plate 15 rigidly connected to the elastic beam 14 is torsionally deformed. Twist angle of shaft ,like Fig.13 As shown, the capacitance value of the sensitive capacitor element 12 is and Produce changes; calculate the change in sensitive capacitance by differential , and then calculate the friction resistance sensed by the sensor ; S32. Perform mechanical calculations; Friction resistance sensed by probe 9 : ; Wherein, A is the force bearing area of ​​the floating element 5; is the friction resistance sensed per unit area by the probe 9; The friction torque transmitted to the elastic beam 14 by the support rod 10 : ; in, 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 14 : ; in, is the shear elastic modulus of single crystal silicon; is the polar moment of inertia of the cross section of the elastic beam 14; is the torsion coefficient; is the height of the elastic beam 14; is the width of the elastic beam 14; is the length of the elastic beam 14; The vibration plate 15 has a friction resistance Torsion angle generated by torque : ; The vibration pole plate 15 generates a torsion angle The differential sensing capacitor : ; in, is the capacitance gap of the sensitive capacitance element 12; , and is the structural parameter of the vibration plate 15; is the dielectric constant of vacuum, ; is Young's modulus; is Poisson's ratio; When the test is not performed, the floating element 5 is in a deflected state, the capacitor plate of the sensitive capacitor element 12 is displaced, and the differential detection capacitor Differential sensing capacitor When conducting wind tunnel tests, the deflection angle of the floating element 5 increases, the displacement of the capacitor plate of the sensitive capacitor element 12 increases, and the capacitance difference is , substituting into formula (5), the capacitance difference caused by airflow is : ; like Fig.14 As shown, the high-speed airflow acts on the wall shear stress of the floating element 5. for: ; in, is the friction coefficient, dynamic pressure .

[0025] Furthermore, the assembly method includes the assembly of the silicon-glass microstructure 8 and the interface circuit 3, the assembly of the floating element 5 and the assembly of the packaging tube shell; The silicon-glass microstructure 8 and the interface circuit 3 are assembled as follows: Fig.15 As shown, align the silicon microstructure 6 and the electrode substrate 7, fix the silicon microstructure 6 on the electrode substrate 7 by epoxy resin, and anodically bond the silicon microstructure 6 and the electrode substrate 7 to obtain a silicon-glass microstructure 8; fix the interface circuit 3 on the fixing table I of the precision visual alignment instrument, align the silicon capacitor installation alignment line 22 of the interface circuit 3 with the alignment line I of the electrode substrate 7, align the floating element installation alignment line 21 of the interface circuit 3 with the marking line of the floating element 5, and fix the silicon-glass microstructure 8 on the interface circuit 3 by epoxy resin; spot weld the lead between the lead electrode 16 and the pad 19 to obtain an assembly of the silicon-glass microstructure 8 and the interface circuit 3; Floating element 5 assembly: Fig.16 As shown, the positioning step 11 of the floating element 5 is inserted into the through hole of the silicon microstructure 6, and the angle of the floating element 5 is rotated so that the marking line on the surface of the probe 9 and the boundary line of the elastic beam 14 of the silicon wafer are perpendicular, and the positioning step 11 is fixed in the through hole by epoxy resin to obtain the assembly of the header structure 2 and the interface circuit 3; Package shell assembly: Fig.17As shown, the package socket 4 is fixed on the fixed table II of the precision visual alignment instrument, the assembly of the interface circuit 3 and the header structure 2 is placed in the groove of the package socket 4, the assembly is clamped by a vacuum suction head, the assembly is moved to the center position, the package cover plate 1 is vertically installed through the package positioning boss 20, the marking lines on the surface of the package shell and the floating element 5 are aligned to ensure the coaxiality and direction of the two, the position of the interface circuit 3 is fixed by epoxy resin, the package shell and the package socket 4 are locked by screws, and the assembly of the common MEMS friction sensor is completed.

[0026] Furthermore, the errors controlled by the assembly method include the coaxial error between the package tube shell and the probe 9 and the flush error between the package tube shell and the floating element 5; Coaxial error: Fig.18 As shown, the coaxial error of the conformal MEMS friction sensor is measured by a precision visual alignment instrument. After the interface circuit 3 is fixed with epoxy resin, the position of the interface circuit 3 is adjusted by a vacuum suction head to ensure that the coaxial error between the package cover plate 1 and the probe 9 is controlled within ±5μm; Flush error: Fig.19 As shown, a reference surface that is at the same height as the center of the floating element 5 is installed on the sensor package tube shell, and the MEMS topography measurement system divides the conformal surface into a number of surface patches through adaptive image segmentation, calculates the relative position relationship between each surface patch and the reference surface, extracts a number of points of each surface patch, calculates the position of the point to the reference plane, marks the height by color, and ensures that the flush error Δh of the sensor is controlled within ±10μm by adding or removing metal gaskets between the package cover plate 1 and the package tube seat 4.

[0027] Furthermore, the assembly method uses deep reactive ion etching technology of single crystal silicon material to process the silicon microstructure 6, and the processing technology includes processes such as photolithography, cavity etching, metal sputtering and deep etching. The electrode substrate 7 is made by Pyrex glass wet etching and metal deposition technology, and the processing technology includes processes such as cleaning, sputtering, photolithography of electrode patterns and removal of excess metal. The interface circuit 3 is made by ceramic-based precision microstrip circuit technology, and the manufacturing process includes the design of the interface circuit 3, the processing of the ceramic substrate and the welding of the interface circuit 3. The floating element 5 is processed by a precision instrument lathe made of duralumin, and the packaging tube shell is processed by precision machining of duralumin. Before processing, this embodiment performs three-dimensional modeling on the cone model, designs the conformal parameters of the conformal MEMS friction sensor, and the conformal surface is processed by an integrated processing technology. First, the planar floating element 5 and the packaging cover plate 1 are processed by precision machining technology, and the processed floating element 5 and the packaging cover plate 1 are fixed by tooling. After the directions of the floating element 5 and the packaging cover plate 1 are marked, the conformal surface is processed in one piece to ensure the consistency of the conformal parameters of the floating element 5 and the packaging cover plate 1.

[0028] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes. For those familiar with the art, all features disclosed in the present invention, or steps in all methods or processes disclosed, except for mutually exclusive features and / or steps, can be combined in any way without departing from the principles of the present invention. The present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A conformal MEMS friction sensor for measuring friction on a cone model surface, characterized in that: The common MEMS friction sensor comprises a packaging tube shell, a header structure (2) and an interface circuit (3); The package tube shell comprises a package cover plate (1) and a package tube base (4) stacked in sequence from top to bottom; wherein a groove is provided at the bottom of the package cover plate (1), and a package positioning boss (20) is provided on the upper surface of the package base; the package cover plate (1) and the package tube base (4) are connected and locked via the groove and the package positioning boss (20); The meter head structure (2) is a sensitive element of a conformal MEMS friction sensor, and converts the friction resistance measured by the conformal MEMS friction sensor into a capacitance signal; the meter head structure (2) comprises a floating element (5), a silicon microstructure (6) and an electrode substrate (7) connected in sequence from top to bottom; the silicon microstructure (6) and the electrode substrate (7) are anodically bonded to form a silicon-glass microstructure (8); The floating element (5) comprises a probe (9), a support rod (10) and a positioning step (11) connected in sequence from top to bottom; wherein the upper surface of the probe (9) and the upper surface of the package cover plate (1) are flush with the conical model, the surfaces of the probe (9) and the package cover plate (1) are conformal, and an annular gap is provided between the probe (9) and the package cover plate (1); the positioning step (11) is embedded in the positioning hole of the silicon microstructure (6) to ensure that the floating element (5) is vertically connected to the silicon microstructure (6); when the probe (9) is subjected to frictional resistance, the probe (9) is deflected by force, and the support rod (10) converts the frictional resistance into a frictional resistance torque and transmits it to the silicon microstructure (6) through the positioning step (11); The silicon microstructure (6) comprises an elastic beam (14), a vibration pole plate (15) and a support frame (13), wherein the silicon microstructure (6) is cut from a rectangular parallelepiped, the vibration pole plate (15) is located at the center of the silicon microstructure (6), and the elastic beam (14) is a beam with two ends fixed and located on both sides of the vibration pole plate (15); the support frame (13) is located around the vibration pole plate (15) and the support frame (13), and supports the vibration pole plate (15) and the floating element (5) through the elastic beam (14); when the floating element (5) transmits a friction torque through the support rod (10), the elastic beam (14) is subjected to a torsion deformation, driving the vibration pole plate (15) to y Deflection of direction; The electrode substrate (7) comprises a lead electrode (16), a glass boss (17) and two Au electrodes (18), wherein the lead electrode (16) is divided into two groups, one on the left and one on the right, and is located on both sides of the electrode substrate (7); each group of lead electrodes (16) extends left and right and converges in the middle to form two Au electrodes (18); the lead electrode (16) is connected to the interface circuit (3) by lead wires; the glass boss (17) is arranged in the remaining area on the upper surface of the electrode substrate (7); the Au electrode (18) and the vibration plate (15) constitute the upper and lower plates of the sensitive capacitor element (12); the glass boss (17) and the support frame (13) are anodic bonded; the upper and lower gaps constitute the capacitor gap of the sensitive capacitor element (12) h 0 When the vibrating plate (15) is deflected by force, the capacitor plate of the sensitive capacitor element (12) is deflected, and the capacitance value of the sensitive capacitor element (12) changes; The interface circuit (3) is a ceramic circuit substrate, which is placed in a groove of a package tube seat (4). A high-frequency micro-capacitance detection chip Pcap01, a single-chip microcomputer STM32F411CEU6, an FPC socket, a plurality of capacitance elements, resistance elements, and a plurality of pads (19) are arranged on the circuit substrate. The pads (19) are connected to lead electrodes (16) by wires. The FPC socket is connected to the interface circuit (3) and a collection computer. The micro-capacitance detection chip converts a differential capacitance signal into a digital signal. The single-chip microcomputer controls the working state of the micro-capacitance detection chip and receives the converted digital signal and sends it to the collection computer. The sampling rate of the interface circuit (3) is 100 Hz.

2. A method for assembling a conformal MEMS friction sensor for measuring friction on a cone model surface, which is used to assemble the conformal MEMS friction sensor for measuring friction on a cone model surface according to claim 1, characterized in that: The assembly method comprises the following steps: S21. The conformal MEMS friction sensor is mounted on the surface of the conical model perpendicular to the generatrix of the conical model; the floating element (5) of the sensor is symmetrical along the neutral plane where the elastic beam (14) is located, and the shape and size of the left and right sides are consistent; S22. When the diameter of the probe (9) is less than or equal to 5 mm, the pressure distribution on both sides of the neutral surface of the elastic beam (14) along the probe (9) is the same, and the surface friction resistance in the direction parallel to the generatrix is ​​directly measured, excluding the pressure difference resistance caused by the pressure imbalance along the airflow direction, so as to realize the friction resistance measurement with automatic deduction of the pressure difference resistance; S23. When the diameter of the probe (9) is greater than 5 mm, the pressure distribution on both sides of the neutral surface of the elastic beam (14) of the probe (9) is also the same; when the wind tunnel test is not performed, the floating element (5) is in a deflected state, the elastic beam (14) is in a torsion state, and the interface circuit (3) outputs the initial value of the capacitance signal; when the wind tunnel test is performed, the deflection angle of the floating element (5) increases, the elastic beam (14) also increases the torsion, and the interface circuit (3) outputs the test value of the capacitance signal; the difference between the initial value of the capacitance signal and the test value of the capacitance signal is calculated to offset the normal force of the sensitive capacitance elements (12) on both sides of the floating element (5) in the static and blowing states, and obtain the capacitance change in the test state, and calculate the surface friction resistance of the floating element (5) through the performance parameters of the sensor and the force-sensitive mechanism of the head structure (2) of the common MEMS friction sensor.

3. The assembly method of the conformal MEMS friction sensor for measuring the friction of the cone model surface according to claim 2 is characterized in that: The force-sensitive mechanism calculation process includes the following steps: S31. Perform mechanical analysis; The probe (9) surface of the floating element (5) is used as a measuring surface and is flush with the wall surface to be measured. The probe (9) senses a force area A that is proportional to the probe (9) and is perpendicular to the Frictional resistance in the axial direction , the support rod (10) reduces the friction resistance Convert to friction torque , friction torque The elastic beam (14) fixed at both ends is torsionally deformed, and the vibration pole plate (15) rigidly connected to the elastic beam (14) is torsionally deformed. Twist angle of shaft , the capacitance value of the sensitive capacitance element (12) and Produce changes; calculate the change in sensitive capacitance by differential , and then calculate the friction resistance sensed by the sensor ; S32. Perform mechanical calculations; Friction resistance sensed by the probe (9) : ； Wherein, A is the force-bearing area of ​​the floating element (5); is the friction resistance per unit area sensed by the probe (9); The friction torque transmitted to the elastic beam (14) through the support rod (10) : ； in, 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 (14) : ； in, is the shear elastic modulus of single crystal silicon; is the polar moment of inertia of the cross section of the elastic beam (14); is the torsion coefficient; is the height of the elastic beam (14); is the width of the elastic beam (14); is the length of the elastic beam (14); The friction torque of the vibrating plate (15) Torsion angle : ； The vibrating pole plate (15) generates a torsion angle The differential sensing capacitor : ； in, is the capacitance gap of the sensitive capacitance element (12); , and are structural parameters of the vibration plate (15); is the dielectric constant of vacuum, ; is Young's modulus; is Poisson’s ratio; When the test is not being performed, the floating element (5) is in a deflected state, the capacitor plate of the sensitive capacitor element (12) is displaced, and the differential detection capacitor Differential sensing capacitor When conducting a wind tunnel test, the deflection angle of the floating element (5) increases, the displacement of the capacitor plate of the sensitive capacitor element (12) increases, and the capacitance difference is , substituting into formula (5), the capacitance difference caused by airflow is for: ； The high-speed airflow exerts shear stress on the wall of the floating element (5) for: ； in, is the friction coefficient, dynamic pressure .

4. The assembly method of the conformal MEMS friction sensor for measuring the friction of the cone model surface according to claim 2, characterized in that: The assembly method comprises the assembly of a silicon-glass microstructure (8) and an interface circuit (3), the assembly of a floating element (5) and the assembly of a packaging tube shell; The silicon-glass microstructure (8) and the interface circuit (3) are assembled as follows: the silicon microstructure (6) and the electrode substrate (7) are aligned, the silicon microstructure (6) is fixed on the electrode substrate (7) by epoxy resin, and the silicon microstructure (6) and the electrode substrate (7) are anodically bonded to obtain the silicon-glass microstructure (8); the interface circuit (3) is fixed on the fixing table I of the precision visual alignment instrument, the silicon capacitor installation alignment line (22) of the interface circuit (3) is aligned with the alignment line I of the electrode substrate (7), the floating element installation alignment line (21) of the interface circuit (3) is aligned with the marking line of the floating element (5), and the silicon-glass microstructure (8) is fixed on the interface circuit (3) by epoxy resin; the lead between the lead electrode (16) and the pad (19) is spot welded to obtain the assembly of the silicon-glass microstructure (8) and the interface circuit (3); Assembling the floating element (5): inserting the positioning step (11) of the floating element (5) into the through hole of the silicon microstructure (6), rotating the angle of the floating element (5) so that the marking line on the surface of the probe (9) and the boundary line of the elastic beam (14) of the silicon wafer are perpendicular, and fixing the positioning step (11) in the through hole with epoxy resin to obtain a combination of the header structure (2) and the interface circuit (3); Package tube shell assembly: fix the package tube seat (4) on the fixed table II of the precision visual alignment instrument, place the assembly of the interface circuit (3) and the header structure (2) in the groove of the package tube seat (4), clamp the assembly by a vacuum suction head, move the assembly to the center position, vertically install the package cover plate (1) through the package positioning boss (20), align the marking lines on the surface of the package tube shell and the floating element (5) to ensure the coaxiality and direction of the two, fix the position of the interface circuit (3) by epoxy resin, lock the package tube shell and the package tube seat (4) by screws, and complete the assembly of the common MEMS friction sensor.

5. The assembly method of the conformal MEMS friction sensor for measuring the friction of the cone model surface according to claim 4, characterized in that: The errors controlled by the assembly method include the coaxial error between the package tube shell and the probe (9) and the flush error between the package tube shell and the floating element (5); Coaxial error: The coaxial error of the conformal MEMS friction sensor is measured by a precision visual alignment instrument. After the interface circuit (3) is fixed with epoxy resin, the position of the interface circuit (3) is adjusted by a vacuum suction head to ensure that the coaxial error between the package cover plate (1) and the probe (9) is controlled within ±5 μm; Flush error: A reference surface with the same height as the center of the floating element (5) is installed on the sensor package tube shell. The MEMS topography measurement system divides the conformal surface into a number of surface patches through adaptive image segmentation, calculates the relative position relationship between each surface patch and the reference surface, extracts a number of points from each surface patch, calculates the position of the point to the reference plane, and marks the height by color. By adding or removing metal gaskets between the package cover plate (1) and the package tube seat (4), the flush error Δh of the sensor is ensured to be controlled within ±10μm.

6. The method for assembling a conformal MEMS friction sensor for measuring friction on a cone model surface according to claim 4, characterized in that: The assembly method adopts deep reactive ion etching technology of single crystal silicon material to process the silicon microstructure (6), and the processing technology includes photolithography, cavity etching, metal sputtering and deep etching. The electrode substrate (7) is manufactured by Pyrex glass wet etching and metal deposition technology, and the processing technology includes cleaning, sputtering, photolithography of electrode pattern and removal of excess metal. The interface circuit (3) is manufactured by ceramic-based precision microstrip circuit technology, and the manufacturing process includes the design of the interface circuit (3), the processing of the ceramic substrate and the welding of the interface circuit (3). The floating element (5) is processed by a hard aluminum material precision instrument lathe, and the packaging tube shell is processed by a hard aluminum material precision machine. The floating element (5) and the packaging cover plate (1) are processed into a common integrated form by a tooling part to ensure that the common parameters of the floating element (5) and the packaging cover plate (1) are consistent.

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