Conformal MEMS Friction Sensors for Measuring the Surface Friction of a Conical Model and Assembly Method

Abstract

The present invention belongs to the technical field of microelectromechanical systems, and discloses a conformal MEMS friction sensor for measuring the surface friction of a conical model and an assembly method thereof. The conformal MEMS friction sensor includes a packaging housing, a head structure and an interface circuit; the packaging housing protects the head structure and the interface circuit through an upper and lower locked packaging cover plate and a packaging base. The conformal MEMS friction sensor is installed on the surface of the conical model perpendicular to the generatrix of the conical model, directly measures the surface friction in the direction parallel to the generatrix, and performs friction measurement with automatic deduction of the pressure difference resistance. 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 packaging housing. The conformal MEMS friction sensor for measuring the surface friction of the conical model and the assembly method thereof of the present invention have the characteristics of small volume, good temperature stability, high reliability, etc., and can accurately measure the frictional resistance on the surface of the conical model.

Description

Technical Field

[0001] The present invention belongs to the technical field of microelectromechanical systems, and particularly relates to a conformal MEMS friction sensor for measuring the surface friction of a conical model and an assembly method thereof. Background Art

[0002] MEMS friction sensors are mainly used to measure the surface friction of aircraft, and then determine the magnitude and distribution of the surface friction of the aircraft, which is of great significance for aircraft design. Traditional surface friction measurement devices are mainly micro-strain friction balances.

[0003] Limited by factors such as sensitivity, temperature, volume and cost, it is difficult to be widely used in the field of aircraft design. MEMS friction sensors based on microelectromechanical 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.

[0004] At present, MEMS friction sensors are divided into comb-tooth capacitive and piezoresistive types, and are mainly used in surface friction measurement experiments in low-speed wind tunnels. In 2001, Jiang Zhe et al. [A MEMS device for measurement of skin friction with capacitive sensing, Microelectromechanical Systems Conference, 24~26 August, 2001[C].] designed a cantilever beam-supported flat differential capacitive MEMS friction sensor with a range of only 0.1~2 Pa, suitable for low-speed wind tunnels. In 2011, Jessica Meloy et al. [Experimental verification of a MEMS based skin friction sensor for quantitative wall shear stress measurement, 41st AIAA Fluid Dynamics Conference and Exhibit, 27~30 June 2011, Honolulu, Hawaii[C].] designed a four-beam-supported comb-tooth capacitive MEMS friction sensor with a range of 0.1~5 Pa. In order not to damage the flow field, the floating element and the comb-tooth capacitor must be exposed to the wind tunnel flow field, and it is only suitable for low-speed wind tunnels with high gas purity.

[0005] Since many application scenarios require surface friction drag testing in the hypersonic wind tunnel flow field, the current testing of the model surface friction drag in the hypersonic wind tunnel flow field still uses the traditional micro friction drag balance. 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 type micro friction drag balance and conducted the friction drag measurement experiment on the model surface in the 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 the surface friction drag of the aircraft. Moreover, the normal load in the hypersonic wind tunnel flow field is large, which puts forward higher requirements for the design and development of MEMS friction sensors.

[0006] In 2014, the Chinese patent literature database published the invention of the inventor team with the invention name of a micro mechanical friction sensor and its manufacturing method (ZL201418003582.X). The floating element of this micro mechanical friction sensor, that is, the MEMS friction sensor, is connected to the elastic beam structure with sensitive capacitive elements through a strut. The surface friction drag sensed by the floating element is transmitted to the elastic beam structure through the strut, driving the sensitive capacitive vibrating plates on both sides of the elastic beam to deflect. The differential of the sensitive capacitors on both sides can calculate the measured surface friction drag. The results of the prototype static calibration and hypersonic wind tunnel verification test show that this MEMS friction sensor has high sensitivity and good stability, and the head structure and packaging form are suitable for the hypersonic wind tunnel test environment. Based on this research, relevant articles were published [Fabrication, calibration and proof experiments in hypersonic wind tunnel for a novel MEMS skin friction sensor, Microsystem Technologies, vol.23, No.8, 2017 [J].].

[0007] In 2022, the Chinese Patent Literature Database published an invention named "A High-Frequency Response and Large-Range MEMS Friction Sensor" (ZL202210154250.5) by the inventor team. This MEMS friction sensor has a measurement bandwidth greater than 3000 Hz, a measurement range of 0 - 1500 Pa, and a resolution better than 2 Pa. It is applicable to shock tunnels with a running time in the millisecond level and high-temperature arc tunnels with a running time in the second level.

[0008] In 2023, the Chinese Patent Literature Database published an invention named "MEMS Friction Sensor for Measuring Friction on Rough Surfaces and Its Fabrication and Design Methods" (ZL202311226952.0) by the inventor team. This MEMS friction sensor has a measurement range of 0 - 100 Pa, a resolution of 0.1 Pa, and a measurement bandwidth of 0 - 200 Hz. 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 applicable to hypersonic flow fields.

[0009] 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 of an aircraft is generally no longer a simple smooth plane, but a special-shaped surface with certain curvature characteristics. The measurement surfaces of the aforementioned MEMS friction sensors are all smooth planes and cannot meet the accurate measurement requirements of the friction on the aircraft surface. In hypersonic wind tunnel test research, the cone model is another typical special-shaped curved surface test research object different from the flat plate model. It is necessary to select the cone model to carry out the co-shaped surface surface friction measurement test research. In the design of an aircraft, there are strict requirements for the co-shaped adaptability between the friction sensor and the aircraft surface, and not all sensors can meet this requirement. The mesoscopic three-dimensional head structure disassembly processing and the characteristics of vision alignment and high-precision micro-assembly technology adopted by the MEMS friction sensors designed by the inventor team (ZL201418003582.X, ZL202210154250.5, ZL202311226952.0) make it feasible to co-shape the processing of the sensor probe and the upper surface of the packaging cover plate, and it has the potential to be co-shaped with the wall surface of the cone model.

[0010] Currently, there is an urgent need to develop a co-shaped MEMS friction sensor for measuring the surface friction of a cone model and its assembly method. Summary of the Invention

[0011] One technical problem to be solved by the present invention is to provide a co-shaped MEMS friction sensor for measuring the surface friction of a cone model, and another technical problem to be solved by the invention is to provide an assembly method for the co-shaped MEMS friction sensor for measuring the surface friction of a cone model, so as to conduct test research on measuring the surface friction resistance of a cone model in a hypersonic wind tunnel.

[0012] The conformal MEMS friction sensor for measuring the surface friction of the conical model of the present invention includes a packaging shell, a head structure, and an interface circuit;

[0013] The packaging shell includes a packaging cover plate and a packaging base stacked in sequence from top to bottom; wherein, a groove is provided at the bottom of the packaging cover plate, a packaging positioning boss is provided on the upper surface of the packaging base, and the packaging cover plate and the packaging base are connected and locked through the groove and the packaging positioning boss;

[0014] The head structure is the sensitive element of the conformal MEMS friction sensor, which converts the frictional resistance measured by the conformal MEMS friction sensor into a capacitance signal; the 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 anodic bonded to form a silicon-glass microstructure;

[0015] The floating element includes a probe head, a support rod, and a positioning step connected in sequence from top to bottom; wherein, the upper surface of the probe head and the upper surface of the packaging cover plate are conformally flush with the conical model, the surfaces of the probe head and the packaging cover plate are conformal, and there is an annular gap between the probe head and the packaging cover plate; 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 head is subjected to frictional resistance, the probe head deflects under force, and the support rod converts the frictional resistance into a frictional resistance moment and transmits it to the silicon microstructure through the positioning step;

[0016] The silicon microstructure includes elastic beams, vibrating plates, and a support frame; wherein, the silicon microstructure is cut from a cuboid, the vibrating plate is at the center of the silicon microstructure, the elastic beams are fixed-end beams at both ends and are located on both sides of the vibrating plate; the support frame is located around the vibrating plate and the support frame, and the vibrating plate and the floating element are supported by the elastic beams; when the floating element transmits the frictional resistance moment through the support rod, the elastic beams are torsionally deformed under force, driving the vibrating plate to y deflect in a certain direction;

[0017] The electrode substrate includes lead electrodes, glass bosses, and 2 Au electrodes; wherein, the lead electrodes are divided into left and right groups and are located on both sides of the electrode substrate. Each group of lead electrodes extends left and right and converges in the middle into 2 Au electrodes. The lead electrodes are connected to the leads of the interface circuit, and glass bosses are provided in the remaining area on the upper surface of the electrode substrate; the Au electrodes and the vibrating plate form the upper and lower plates of the sensitive capacitance element, and the glass bosses and the support frame are anodic bonded, and the upper and lower gaps form the capacitance gap of the sensitive capacitance element h 0 ; when the vibrating plate deflects under force, the capacitance plates of the sensitive capacitance element deflect, and the capacitance value of the sensitive capacitance element changes;

[0018] The interface circuit mentioned above is a ceramic board circuit substrate. The circuit substrate is placed in the groove of the packaging socket. On the circuit substrate, there are arranged a high-frequency micro-capacitance detection chip Pcap01, a single-chip microcomputer STM32F411CEU6, an FPC socket, various capacitance elements, resistance elements, and several pads. The pads are connected to the lead electrodes by leads. The FPC socket connects the interface circuit 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, receives the converted digital signal, and sends it to the acquisition computer. The sampling rate of the interface circuit is 100Hz.

[0019] The assembly method of the conformal MEMS friction sensor for measuring the surface friction of the conical model in the present invention includes the following steps:

[0020] S21. Install the conformal MEMS friction sensor perpendicular to the generatrix of the conical model on the surface of the conical model; the floating element of the sensor is symmetric along the neutral plane where the elastic beam is located, and the shapes and sizes on the left and right sides are the same;

[0021] S22. When the diameter of the probe head is less than or equal to 5mm, the pressure distribution on both sides of the neutral plane of the elastic beam by the probe head is the same. Directly measure the surface friction in the direction parallel to the generatrix, excluding the pressure difference resistance generated by the pressure imbalance along the air flow direction, and realize the friction measurement that automatically deducts the pressure difference resistance;

[0022] S23. When the diameter of the probe head is greater than 5mm, the pressure distribution on both sides of the neutral plane of the elastic beam by the probe head is also the same; when no wind tunnel test is carried out, the floating element is in a deflected state, the elastic beam is in a torsional state, and the interface circuit outputs the initial value of the capacitance signal; when a wind tunnel test is carried out, the deflection angle of the floating element increases, the elastic beam also increases in torsion, and the interface circuit outputs the test value of the capacitance signal; find the difference between the initial value of the capacitance signal and the test value of the capacitance signal, cancel the normal forces of the sensitive capacitance elements on both sides of the floating element in the static and blowing states, obtain the transformation amount of the capacitance in the test state, and calculate the surface friction resistance of the floating element through the performance parameters of the sensor and the force-sensitive mechanism of the head structure of the conformal MEMS friction sensor.

[0023] Further, the force-sensitive mechanism calculation process includes the following steps:

[0024] S31. Conduct mechanical analysis;

[0025] The probe head surface of the floating element serves as the measurement surface and is conformal and flush with the wall surface to be measured. The friction resistance sensed by the probe head is proportional to the force-receiving area A of the probe head and is perpendicular to the axis direction , and the strut converts the friction resistance into a frictional torque , and the frictional torque A torsion deformation is generated in an elastic beam fixed at both ends, and a vibrating plate rigidly connected to the elastic beam generates a torsional angle around the axis , and the capacitance value of the sensitive capacitance element and changes; by calculating the change amount of the sensitive capacitance through differential calculation , and then calculating the frictional resistance sensed by the sensor ;

[0026] S32. Perform mechanical calculations;

[0027] The frictional resistance sensed by the probe :

[0028] ;

[0029] where A is the force-bearing area of the floating element; is the frictional resistance sensed per unit area of the probe;

[0030] The frictional torque transmitted to the elastic beam through the support rod :

[0031] ;

[0032] where is the distance between the upper surface of the probe and the center line of the torsional axis;

[0033] The torsional elastic coefficient of the elastic beam :

[0034] ;

[0035] where is the shear elastic modulus of single crystal silicon; is the polar moment of inertia of the cross section of the elastic beam; is the torsional coefficient; is the height of the elastic beam; is the width of the elastic beam; is the length of the elastic beam;

[0036] The vibrating plate generates a torsional angle under the action of the frictional torque :

[0037] ;

[0038] The differential detection capacitance after the vibrating plate generates a torsional angle :

[0039] ;

[0040] Among them, is the capacitance gap of the sensitive capacitance element; , and are the structural parameters of the vibrating plate; is the vacuum permittivity, ; is the Young's modulus; is the Poisson's ratio;

[0041] When no test is carried out, the floating element is in a deflected state, the capacitance plates of the sensitive capacitance element generate displacement, and the differential detection capacitance is the differential detection capacitance ; when a wind tunnel test is carried out, the deflection angle of the floating element increases, the displacement of the capacitance plates of the sensitive capacitance element becomes larger, and the generated capacitance difference is . Substituting it into formula (5), the capacitance difference generated by the action of the air flow is :

[0042] ;

[0043] The wall shear stress of the high-speed air flow acting on the floating element is:

[0044] ;

[0045] Among them, is the friction coefficient, and the dynamic pressure .

[0046] Furthermore, 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 packaging shell;

[0047] The assembly of the silicon-glass microstructure and the interface circuit: Align the silicon microstructure with the electrode substrate, fix the silicon microstructure on the electrode substrate through epoxy resin, and obtain the silicon-glass microstructure by anodic bonding of the silicon microstructure and the electrode substrate; Fix the interface circuit on the fixing table Ⅰ of the precision vision alignment instrument, align the silicon capacitance installation alignment line of the interface circuit with the alignment line Ⅰ of the electrode substrate, align the floating element installation alignment line of the interface circuit with the marking line of the floating element, and fix the silicon-glass microstructure on the interface circuit through epoxy resin; Spot-weld the leads between the lead electrodes and the pads to obtain the assembly of the silicon-glass microstructure and the interface circuit;

[0048] The assembly of the floating element: 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 surface of the probe head is perpendicular to the elastic beam boundary line of the silicon wafer, and fix the positioning step in the through hole through epoxy resin to obtain the combined component of the head structure and the interface circuit;

[0049] Encapsulation housing assembly: Fix the encapsulation base on the fixed table II of the precision vision alignment instrument. Place the assembly of the interface circuit and the meter head structure in the groove of the encapsulation base. Clamp the assembly with a vacuum chuck, move the assembly to the center position, vertically install the encapsulation cover plate through the encapsulation positioning boss, align the marking lines on the encapsulation housing and the surface of the floating element to ensure their coaxiality and consistent direction. Fix the position of the interface circuit with epoxy resin, and lock the encapsulation housing and the encapsulation base with screws to complete the assembly of the conformal MEMS friction sensor.

[0050] Furthermore, the errors controlled by the assembly method include the coaxial error between the encapsulation housing and the probe head and the flush error between the encapsulation housing and the floating element.

[0051] Coaxial error: Measure the coaxial error of the conformal MEMS friction sensor with a precision vision alignment instrument. After fixing the position of the interface circuit with epoxy resin, adjust the position of the interface circuit with a vacuum chuck to ensure that the coaxial error between the encapsulation cover plate and the probe head is controlled within ±5μm.

[0052] Flush error: Install a reference surface with the same center height as the floating element on the sensor encapsulation housing. 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 of the points 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 subtracting metal gaskets between the encapsulation cover plate and the encapsulation base.

[0053] Furthermore, for the silicon micro-structure in the assembly method, deep reactive ion etching technology with single-crystalline silicon material is used for processing, and the processing technology includes photolithography, cavity etching, metal sputtering, and deep etching. The electrode substrate is fabricated by wet etching of Pyrex glass and metal deposition technology, and the processing technology includes cleaning, sputtering, photolithography of electrode patterns, and removal of excess metal. The interface circuit is fabricated 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 machined with a precision instrument lathe using hard aluminum material, and the encapsulation housing is machined with precision machinery using hard aluminum material. The floating element and the encapsulation cover plate are processed in a conformal integration manner through tooling parts to ensure that the conformal parameters of the floating element and the encapsulation cover plate are consistent.

[0054] The conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention and its assembly method adopt a conical conformal surface to realize the conformal surface measurement ability of the MEMS friction sensor. The measurement range is 0 - 100 Pa, the resolution is better than 0.2 Pa, and the measurement bandwidth is 0 - 100 Hz. It has the characteristics of small volume, good temperature stability, and high reliability, and can accurately measure the frictional resistance on the surface of the conical model. Description of the Drawings

[0055] Figure 1 It is a schematic diagram of the overall structure of the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0056] Figure 2 It is an exploded view of the overall structure of the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0057] Figure 3 It is an exploded view of the head structure of the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0058] Figure 4 It is a schematic diagram of the floating element structure in the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0059] Figure 5 It is a schematic diagram of the silicon microstructure in the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0060] Figure 6 It is a schematic diagram of the electrode substrate structure in the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0061] Figure 7 It is a schematic diagram of the silicon - glass bonding structure in the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0062] Figure 8 It is a schematic diagram of the interface circuit structure in the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0063] Figure 9 It is a schematic diagram of the package socket structure in the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0064] Figure 10 It is a schematic diagram of the conformal installation of the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0065] Figure 11 It is a schematic diagram of the installation of the conformal MEMS friction sensor for measuring the surface friction of a conical model of the present invention;

[0066] Figure 12 Installation cross-sectional view of the conformal MEMS friction sensor for measuring the surface friction of the conical model of the present invention;

[0067] Figure 13 Schematic diagram of the working principle of the conformal MEMS friction sensor for measuring the surface friction of the conical model of the present invention;

[0068] Figure 14 Force analysis diagram of the conformal MEMS friction sensor for measuring the surface friction of the conical model of the present invention;

[0069] Figure 15 Assembly schematic diagram of the silicon-glass microstructure and interface circuit of the conformal MEMS friction sensor for measuring the surface friction of the conical model of the present invention;

[0070] Figure 16 Assembly schematic diagram of the floating element of the conformal MEMS friction sensor for measuring the surface friction of the conical model of the present invention;

[0071] Figure 17 Assembly schematic diagram of the package housing of the conformal MEMS friction sensor for measuring the surface friction of the conical model of the present invention;

[0072] Figure 18 Schematic diagram of the coaxial error of the conformal MEMS friction sensor for measuring the surface friction of the conical model of the present invention;

[0073] Figure 19 Schematic diagram of the flush error of the conformal MEMS friction sensor for measuring the surface friction of the conical model of the present invention.

[0074] In the figure, 1. Package cover plate; 2. Gauge head structure; 3. Interface circuit; 4. Package base; 5. Floating element; 6. Silicon microstructure; 7. Electrode substrate; 8. Silicon-glass microstructure; 9. Probe; 10. Support rod; 11. Positioning step; 12. Sensitive capacitance 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 capacitance installation alignment line. Detailed implementation manners

[0075] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0076] Embodiment: As Figure 1 、 Figure 2As shown, the structure of the conformal MEMS friction sensor for measuring the surface friction of the conical model in this embodiment is decomposed into a packaging cover plate 1, a sensor head structure 2, an interface circuit 3, and a packaging base 4. After high-precision machining of each component, they are micro-assembled and integrated; as Figure 3 shown, the sensor head structure 2 includes a floating element 5, a silicon microstructure 6, and an electrode substrate 7. As Figure 4 shown, the floating element 5 includes a probe 9, a support rod 10, and a positioning step 11. As Figure 5 shown, the silicon microstructure 6 includes a support frame 13, elastic beams 14, and vibrating plates 15. As Figure 6 shown, the electrode substrate 7 includes lead electrodes 16, glass bosses 17, and Au electrodes 18. As Figure 7 shown, the silicon microstructure 6 and the electrode substrate 7 are anodically bonded to obtain a silicon-glass microstructure 8. The vibrating plates 15 of the silicon microstructure 6 and the Au electrodes 18 of the electrode substrate 7 form a differential sensitive capacitance element 12 to achieve differential capacitance detection. As Figure 8 shown, the interface circuit 3 is a ceramic board circuit substrate. On the circuit substrate, a high-frequency micro-capacitance detection chip Pcap01, a single-chip microcomputer STM32F411CEU6, an FPC socket, resistance elements, various capacitance elements, and pads 19 are arranged.

[0077] The described packaging shell includes a packaging cover plate 1 and a packaging base 4 stacked on top of each other from top to bottom; among them, a groove is provided at the bottom of the packaging cover plate 1, and a packaging positioning boss 20 is provided on the upper surface of the packaging base. As Figure 9 shown, the packaging cover plate 1 and the packaging base 4 are connected and locked through the groove and the packaging positioning boss 20;

[0078] The described sensor head structure 2 is the sensitive element of the conformal MEMS friction sensor, which converts the friction resistance measured by the conformal MEMS friction sensor into a capacitance signal; the sensor 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;

[0079] The described floating element 5 includes a probe 9, a support rod 10, and a positioning step 11 connected in sequence from top to bottom; among them, the upper surface of the probe 9 and the upper surface of the packaging cover plate 1 are conformal and flush with the conical model. The surfaces of the probe 9 and the packaging cover plate 1 are conformal, and there is an annular gap between the probe 9 and the packaging 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 deflects under the force, and the support rod 10 converts the friction resistance into a friction resistance torque and transmits it to the silicon microstructure 6 through the positioning step 11;

[0080] The silicon microstructure 6 described above includes elastic beams 14, vibrating plates 15 and a support frame 13. Among them, the silicon microstructure 6 is cut from a cuboid. The vibrating plate 15 is at the center of the silicon microstructure 6. The elastic beams 14 are fixed-ended beams at both ends and are located on both sides of the vibrating plate 15. The support frame 13 is located around the vibrating plate 15 and the support frame 13, and supports the vibrating plate 15 and the floating element 5 through the elastic beams 14. When the floating element 5 transmits the frictional torque through the support rod 10, the elastic beams 14 are stressed and twisted, driving the vibrating plate 15 to y deflect in a certain direction;

[0081] The electrode substrate 7 described above includes lead electrodes 16, glass bosses 17 and two Au electrodes 18. Among them, the lead electrodes 16 are divided into left and right groups and are 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 electrodes 16 are wire-connected to the interface circuit 3 leads. Glass bosses 17 are arranged in the remaining area on the upper surface of the electrode substrate 7. The Au electrodes 18 and the vibrating plate 15 form the upper and lower plates of the sensitive capacitance element 12. The glass bosses 17 and the support frame 13 are anodic bonded, and the upper and lower gaps form the capacitance gap of the sensitive capacitance element 12 h 0 ; When the vibrating plate 15 is deflected by force, the capacitance plates of the sensitive capacitance element 12 are deflected, and the capacitance value of the sensitive capacitance element 12 changes;

[0082] The interface circuit 3 is a ceramic board circuit substrate. The circuit substrate is placed in the groove of the package socket 4. The circuit substrate is arranged with a high-frequency micro-capacitance detection chip Pcap01, a single-chip microcomputer STM32F411CEU6, an FPC socket, various capacitance elements, resistance elements and several pads 19. The pads 19 are wire-connected to the lead electrodes 16. The FPC socket 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.

[0083] The assembly method of the conformal MEMS friction sensor for measuring the surface friction of the conical model in this embodiment. According to the fact that the surface of the probe 9 of the conformal MEMS friction sensor is parallel to the generatrix of the conical model, a conformal installation is adopted in which the support rod 10 of the floating element 5 is perpendicular to the generatrix of the conical model. As Figure 10 shown, the conformal MEMS friction sensor is installed perpendicular to the generatrix of the conical model on the surface of the conical model;

[0084] The assembly method utilizes the fact that the sensor floating element 5 is symmetric about the neutral plane where the elastic beam 14 is located, and the shapes and sizes on the left and right sides are the same. When the diameter of the probe 9 is less than or equal to 5 mm, without considering the pressure change along the flow direction, the pressure distribution on both sides of the neutral plane of the elastic beam 14 by the probe 9 is the same. It directly measures the surface friction resistance in the direction of the parallel generatrix, without including the pressure difference resistance caused by the pressure imbalance along the air flow direction, and realizes the friction resistance measurement that automatically deducts the pressure difference resistance.

[0085] At the same time, the floating element 5 is symmetric about the neutral plane where the elastic beam 14 is located. When the conformal MEMS friction sensor measures on the conical model surface, changing the direction does not affect the measurement result; the strut 10 of the floating element 5 is perpendicular to the generatrix of the conical model, and the surface of the probe 9 is parallel to the generatrix of the conical model. The shapes and sizes of the conformal structures at any position in the direction of the conical model generatrix are the same. As Figure 11 、 Figure 12 shown, installing the conformal MEMS friction sensor at any position along the generatrix of the conical model also does not affect the measurement result.

[0086] Install the conformal MEMS friction sensor perpendicular to the normal of the conical model on the conical model surface. The areas on both sides of the center line of the floating element 5 are the same; when no wind tunnel test is carried out, the floating element 5 is in a deflected state, the elastic beam 14 is in a torsional state, and the interface circuit 3 outputs the initial value of the capacitance signal; when a wind tunnel test is carried out, the deflection angle of the floating element 5 increases, the elastic beam 14 increases torsion, and the interface circuit 3 outputs the test value of the capacitance signal; find the difference between the initial value of the capacitance signal and the test value of the capacitance signal, cancel the normal forces on the sensitive capacitance elements 12 on both sides of the floating element 5 in the static and blowing states, obtain the change amount of the capacitance 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 conformal MEMS friction sensor.

[0087] Furthermore, the force-sensitive mechanism calculation process includes the following steps:

[0088] S31. Conduct mechanical analysis;

[0089] The surface of the probe 9 of the floating element 5 is used as the measurement surface and is conformal and flush with the wall surface to be measured. The probe 9 senses the frictional resistance that is proportional to the force-bearing area A of the probe 9 and perpendicular to the axis direction , and the strut 10 converts the frictional resistance into a frictional torque , and the frictional torque causes the elastic beam 14 with both ends fixed to produce torsional deformation, and the vibrating plate 15 rigidly connected to the elastic beam 14 generates a torsional angle about the axis, as Figure 13 shown, the capacitance value and generate changes; calculate the change amount of the sensitive capacitance through differential calculation and then calculate the frictional resistance sensed by the sensor ;

[0090] S32. Perform mechanical calculations;

[0091] The frictional resistance sensed by the probe 9 :

[0092] ;

[0093] where A is the force-bearing area of the floating element 5; is the frictional resistance sensed per unit area by the probe 9;

[0094] The frictional torque transmitted to the elastic beam 14 through the support rod 10 :

[0095] ;

[0096] where, is the distance between the upper surface of the probe 9 and the center line of the torsion shaft;

[0097] The torsional elastic coefficient of the elastic beam 14 :

[0098] ;

[0099] where, 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;

[0100] The vibrating plate 15 generates a torsional angle under the action of the frictional torque : :

[0101] ;

[0102] The vibrating plate 15 generates a torsional angle and the differential detection capacitance after that :

[0103] ;

[0104] where, is the capacitance gap of the sensitive capacitance element 12; 、 and are the structural parameters of the vibrating plate 15; is the vacuum permittivity, ; is the Young's modulus; is the Poisson's ratio;

[0105] When no test is carried out, the floating element 5 is in a deflected state, the capacitor plates of the sensitive capacitor element 12 generate displacement, and the differential detection capacitor is the differential detection capacitor ; When a wind tunnel test is carried out, the deflection angle of the floating element 5 increases, the displacement of the capacitor plates of the sensitive capacitor element 12 becomes larger, and the generated capacitance difference is , substituting into formula (5), the capacitance difference generated by the airflow action is :

[0106] ;

[0107] Such as Figure 14 shown, the wall shear stress acting on the floating element 5 by the high-speed airflow is

[0108] ;

[0109] Among them, is the friction coefficient, and the dynamic pressure .

[0110] 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 shell;

[0111] The assembly of the silicon-glass microstructure 8 and the interface circuit 3: As Figure 15 shown, align the silicon microstructure 6 with the electrode substrate 7, fix the silicon microstructure 6 on the electrode substrate 7 through epoxy resin, and perform anodic bonding on the silicon microstructure 6 and the electrode substrate 7 to obtain the silicon-glass microstructure 8; Fix the interface circuit 3 on the fixing table I of the precision vision 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 through epoxy resin; Spot-weld the lead between the lead electrode 16 and the pad 19 to obtain the assembly of the silicon-glass microstructure 8 and the interface circuit 3;

[0112] The assembly of the floating element 5: As Figure 16As shown, insert the positioning step 11 of the floating element 5 into the through-hole of the silicon micro-structure 6, rotate the floating element 5 to make the marked line on the surface of the probe 9 perpendicular to the boundary line of the elastic beam 14 of the silicon wafer, and fix the positioning step 11 in the through-hole with epoxy resin to obtain the assembly of the head structure 2 and the interface circuit 3;

[0113] Encapsulation housing assembly: As Figure 17 shown, fix the encapsulation base 4 on the fixed stage II of the precision vision alignment instrument, place the assembly of the interface circuit 3 and the head structure 2 in the groove of the encapsulation base 4, clamp the assembly with a vacuum chuck, move the assembly to the center position, vertically install the encapsulation cover plate 1 through the encapsulation positioning boss 20, align the marked lines on the surfaces of the encapsulation housing and the floating element 5 to ensure the coaxiality and consistent direction of the two, fix the position of the interface circuit 3 with epoxy resin, and lock the encapsulation housing and the encapsulation base 4 with screws to complete the assembly of the conformal MEMS friction sensor.

[0114] Furthermore, the errors controlled by the assembly method include the coaxial error between the encapsulation housing and the probe 9 and the flush error between the encapsulation housing and the floating element 5;

[0115] Coaxial error: As Figure 18 shown, measure the coaxial error of the conformal MEMS friction sensor through a precision vision alignment instrument. After fixing the position of the interface circuit 3 with epoxy resin, adjust the position of the interface circuit 3 with a vacuum chuck to ensure that the coaxial error between the encapsulation cover plate 1 and the probe 9 is controlled within ±5 μm;

[0116] Flush error: As Figure 19 shown, install a reference surface with the same center height as the floating element 5 on the sensor encapsulation housing. 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 of each surface patch, calculates the position of the points to the reference plane, marks the height with color, and ensures that the flush error Δh of the sensor is controlled within ±10 μm by adding or subtracting metal gaskets between the encapsulation cover plate 1 and the encapsulation base 4.

[0117] Further, for the silicon microstructure 6, the deep reactive ion etching technology of single-crystal silicon material is adopted in the assembly method, and the processing technology includes photolithography, cavity etching, metal sputtering, deep etching and other processes. The electrode substrate 7 is fabricated by wet etching of Pyrex glass and metal deposition technology, and the processing technology includes cleaning, sputtering, photolithography of electrode patterns, and removal of excess metal and other processes. The interface circuit 3 is fabricated 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 machined by a precision instrument lathe using hard aluminum material, and the package case is machined by precision machining using hard aluminum material. Before processing, in this embodiment, a three-dimensional model of the conical model is established, the conformal parameters of the conformal MEMS friction sensor are designed, and the conformal surface is processed by an integrated processing technology. First, the planar floating element 5 and the package cover 1 are processed by precision machining technology, the processed floating element 5 and the package cover 1 are fixed by a tooling, and after marking the directions of the floating element 5 and the package cover 1, the integrated processing of the conformal surface is carried out to ensure the consistency of the conformal parameters of the floating element 5 and the package cover 1.

[0118] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and embodiments. For those skilled in the art, without departing from the principle of the present invention, all the features disclosed in the present invention, or all the steps in the disclosed methods or processes, except for the mutually exclusive features and / or steps, can be combined in any way. The present invention is not limited to the specific details and the illustrated examples here.

Claims

1. A method for assembling a conformal MEMS friction sensor for measuring friction on a cone model surface, which is used to assemble a conformal MEMS friction sensor for measuring friction on a cone model surface, and is 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 the 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. 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.

2. The assembly method of the conformal MEMS friction sensor for measuring the friction of the cone model surface according to claim 1 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; Frictional 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 centerline 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 .

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 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.

4. The assembly method of the conformal MEMS friction sensor for measuring the friction of the cone model surface according to claim 3 is 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.

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 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, and 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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