Static calibration method for wall shear stress sensor of floating element

Abstract

The invention relates to a static calibration method for a floating element wall surface shear stress sensor. The static calibration method comprises the following steps: fixing a flexible rod on an electric precision displacement table; the free end of the flexible rod is fixedly connected with the micro-force probe, and the free end of the micro-force probe is in contact with the side surface of the mass block; the mass block is in contact with the floating element sensitive chip and does not slide relative to the floating element sensitive chip; the floating element outputs a force measured by the calibrated wall surface shear stress sensor; the electric precision displacement table is controlled to generate target force, the deformation quantity of the flexible flexible rod is obtained based on the displacement of the electric precision displacement table and the displacement of the micro-force probe, and then the force borne by the flexible flexible rod is obtained; calculating the wall surface shear stress transmitted to the floating element by the mass block; obtaining a first error between the target force and the wall surface shear stress transmitted to the floating element by the mass block; if the first error exceeds the allowable range, the contact position of the micro-force probe and the side surface of the mass block is adjusted; and judging whether the calibrated wall surface shear stress sensor is qualified or not according to the target force and the measured force.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical metrology, and in particular to a static calibration method for a floating element wall shear stress sensor. Background Art

[0002] Wall shear stress is the viscous drag generated by fluid passing over an object's surface. It helps determine flow transitions, separation, and reattachment within the boundary layer and is a key parameter for evaluating aircraft equipment performance and surface friction distribution. Accurately measuring wall shear stress can further understand the internal structure of the boundary layer, monitor the motion of the fluid surrounding the aircraft, and prevent stall caused by flow separation, thus playing a vital role in maintaining aircraft flight safety. Accurately measuring wall shear stress is also crucial for understanding the viscous drag of aircraft and optimizing their structure. Reducing wall shear stress can reduce vehicle energy consumption and improve performance.

[0003] Although research on wall shear stress sensors has been going on for more than 20 years at home and abroad, there is currently little research on methods for calibrating wall shear stress sensors, and there is a lack of a static calibration method for wall shear stress sensors that takes into account both high precision and a large range. Summary of the Invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide a static calibration method for a floating element wall shear stress sensor, so as to solve the problem in the prior art of lacking a static calibration method for a wall shear stress sensor with both high precision and a large range.

[0005] An embodiment of the present invention provides a static calibration method for a floating element wall shear stress sensor, the method comprising: fixing one end of a flexible flexure rod assembly on an electric precision translation stage; fixedly connecting the free end of the flexible flexure rod assembly to the fixed end of a micro-force probe, wherein the free end of the micro-force probe contacts the side surface of a mass block to achieve force transmission; contacting the mass block with a sensitive chip of the floating element without relative sliding, so that the mass block transmits force to the floating element through static friction; the floating element senses the magnitude of the force and outputs the force measured by the calibrated wall shear stress sensor;

[0006] The electric precision translation stage is controlled to generate a target force, and the displacement of the micro-force probe is measured. The deformation of the flexible rod is obtained based on the displacement of the electric precision translation stage and the displacement of the micro-force probe, and the force F acting on the flexible rod is further obtained. The wall shear stress of the floating element transmitted by the mass block to the floating element is calculated based on the force F acting on the flexible rod and the contact area between the mass block and the floating element.

[0007] Obtaining a first error between the target force and the wall shear stress transmitted by the mass block to the floating element; if the first error exceeds an allowable range, adjusting the contact position between the free end of the micro-force probe and the side surface of the mass block until the error is within the allowable range;

[0008] Whether the calibrated wall shear stress sensor is qualified is judged according to the target force generated by the electric precision translation stage and the force measured by the calibrated wall shear stress sensor.

[0009] Furthermore, the calculation formula for the deformation variable Δx of the flexible flexure is:

[0010] Δx=x2-x1

[0011] Where x2 is the displacement of the micro-force probe, and x1 is the displacement of the electric precision translation stage.

[0012] Furthermore, the force F generated by the flexible flexible rod is calculated based on the stiffness k and the deformation of the flexible flexible rod. The calculation formula is:

[0013] F = k·(x2-x1).

[0014] Furthermore, if the first error exceeds the allowable range, the contact position between the free end of the micro-force probe and the side surface of the mass block is adjusted so that the lowest point of the free end of the micro-force probe is directly below the center point of the side surface of the mass block.

[0015] Furthermore, during the calibration process, the relative sliding between the mass block and the floating element sensitive chip is observed in real time through a zoom camera. If relative sliding occurs between the two, when the force measured by the calibrated wall shear stress sensor is in the range of 0.1-300Pa, the mass of the mass block is increased to ensure that no relative sliding occurs between the mass block and the floating element sensitive chip.

[0016] Furthermore, a rubber pad with a first thickness is adhered to the lower end of the mass block, and the rubber pad is in direct contact with the upper surface of the floating element. During the calibration process, the relative sliding between the mass block and the sensitive chip of the floating element is observed in real time through a zoom camera. If relative sliding occurs between the two, when the force range measured by the calibrated wall shear stress sensor is between 300-500Pa, the roughness of the rubber pad adhered under the mass block is increased to ensure that no relative sliding occurs between the mass block and the sensitive chip of the floating element.

[0017] Furthermore, judging whether the calibrated wall shear stress sensor is qualified according to the target force generated by the electric precision translation stage and the force measured by the calibrated wall shear stress sensor includes:

[0018] Step 1: A target force generated by the electric precision translation stage is used as the horizontal coordinate, with the deformation variable Δx of the flexible flexure as the horizontal coordinate and the force measured by the calibrated wall shear stress sensor as the vertical coordinate to form a measurement point;

[0019] Step 2: Repeatedly apply multiple different target forces and record the deformation Δx of the corresponding flexible rod and the force measured by the calibrated wall shear stress sensor to form multiple measurement points;

[0020] Step 3: Fitting the multiple measurement points into a second straight line; using different target forces output by the electric precision translation stage as the ordinate and the deformation variable Δx of the corresponding flexible flexure as the abscissa to form multiple target points, and fitting the multiple target points into a first straight line;

[0021] Step 4: Within the measuring range of the calibrated wall shear stress sensor, determine the maximum value of the difference between the measured force and the target force generated by the deformation Δx of the corresponding flexible rod on the second straight line and the first straight line. Divide the maximum value of the difference between the measured force and the target force by the difference between the upper and lower limits of the measuring range of the calibrated wall shear stress sensor to obtain the linear error.

[0022] Step 5: Determine whether the calibrated wall shear stress sensor is qualified based on whether the linear error is within the nominal accuracy range of the calibrated wall shear stress sensor.

[0023] Furthermore, the floating element includes a fixed end and a movable end; the fixed end is a U-shaped silicon substrate, the movable end is a floating element sensitive chip, and folded tethers are symmetrically arranged on both sides of the floating element sensitive chip and fixedly connected to the inner walls of the left and right ends of the silicon substrate; the floating element sensitive chip is a sensitive component of the wall shear stress sensor; the floating element sensitive chip is provided with a wall shear stress output interface.

[0024] Furthermore, the folding tether is designed to be spiral and can produce elastic deformation; the folding tether is made of aluminum alloy.

[0025] Furthermore, during calibration, a calibration device including an electric precision translation stage, a flexible flexure rod assembly, a micro-force probe, a mass block, and a floating element is installed on a vibration isolation table, and an organic glass shell is set outside the calibration device and the vibration isolation table to reduce the influence of vibration and air circulation.

[0026] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0027] 1. The target force generated by the calibration method of the present invention comes from the electric precision displacement stage, and the target force is transmitted to the flexible rod, which is then transmitted to the mass block through the deformation of the flexible rod. The force generated and transmitted in this process is stable.

[0028] 2. The present invention is based on the main structure of the flexible rod and uses the displacement of the micro-force probe measured by laser interferometer to achieve precise measurement of the displacement of the tail of the flexible rod, ensuring the accuracy of the force value and meeting high-precision requirements.

[0029] 3. The present invention is based on the design of a micro-force probe to adapt to the small-sized structure of the floating element sensitive chip and complete the force transmission.

[0030] 4. The calibration method of the present invention produces a stable target force value with micro-nano Newton accuracy. When the confidence coefficient k = 2, the measurement uncertainty U = 0.06%; the mass block is attached with a rubber pad. By changing the roughness of the rubber pad or the mass of the mass block, the measuring range can be increased without losing the measurement accuracy. The wall shear stress range that can be calibrated is 0.1-500Pa, the repeatability error is better than 0.5%, the accuracy is better than 0.2%, and the maximum force resolution is better than 0.1Pa.

[0031] 5. The present invention calculates the linear error by fitting multiple measurement points into a second straight line and multiple points corresponding to target forces into a first straight line, thereby completing the calibration process quickly and having a short response time.

[0032] 6. By fixing the entire calibration device on a vibration isolation table and shielding it with a plexiglass shell, the effects of vibration and air circulation are minimized to ensure stable environmental conditions. Therefore, the measurement environment requirements of the present invention are relatively relaxed, and high-precision calibration can be achieved in complex environments.

[0033] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0035] Figure 1 A flow chart of a static calibration method for a floating element wall shear stress sensor;

[0036] Figure 2 A schematic diagram of the structure of a calibration device for a static calibration method of a floating element wall shear stress sensor;

[0037] Reference numerals:

[0038] 1-Electric precision translation stage;

[0039] 2-Fix bracket;

[0040] 3-Flexible rod;

[0041] 4-Micro force probe;

[0042] 5-mass block;

[0043] 6-Rubber pad;

[0044] 7-Silicon substrate;

[0045] 8-Floating element sensitive chip;

[0046] 9-Folding tether;

[0047] 10-Laser interferometer. DETAILED DESCRIPTION

[0048] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0049] A specific embodiment of the present invention discloses a static calibration method for a floating element wall shear stress sensor. The static calibration method flow chart is as follows: Figure 1 The specific method includes steps S1-S4.

[0050] S1. Fix one end of the flexible rod 3 assembly on the electric precision translation stage 1; the free end of the flexible rod 3 assembly is fixedly connected to the fixed end of the micro-force probe 4, and the free end of the micro-force probe 4 contacts the side surface of the mass block 5 to realize force transmission; the mass block 5 contacts the floating element sensitive chip 8 without relative sliding, so that the mass block 5 transmits the force to the floating element through static friction; the floating element senses the magnitude of the force and outputs the force measured by the calibrated wall shear stress sensor.

[0051] The schematic diagram of the calibration device is as follows: Figure 2 shown.

[0052] Specifically, the flexible flexible rod 3 assembly transmits the received target force to the micro-force probe 4; the micro-force probe 4 then transmits the target force to the floating element through the mass block 5; the flexible flexible rod 3 assembly includes a flexible flexible rod 3 and a fixed bracket 2, and the flexible flexible rod 3 and the fixed bracket 2 are an integrated structure. The upper end of the flexible flexible rod 3 is fixed to the lower surface of the fixed bracket 2 as a fixed end; the lower end of the flexible flexible rod 3 is a free end; one end of the micro-force probe 4 is fixedly connected to the free end of the flexible flexible rod 3, and the other end is in contact with one side of the mass block 5; the micro-force probe 4 is a rectangular structure, and the short side of the rectangle is welded to the lower surface of the free end of the flexible flexible rod 3.

[0053] The mass block 5 is placed above the floating element. A rubber pad 6 with a first thickness is attached to the lower end of the mass block 5, and the rubber pad 6 is in direct contact with the upper surface of the floating element.

[0054] The floating element includes a fixed end and a movable end; the fixed end is a U-shaped silicon substrate 7, and the movable end is a floating element sensitive chip 8. Folding tethers 9 are symmetrically arranged on both sides of the floating element sensitive chip 8 and fixedly connected to the inner side walls of the left and right ends of the silicon substrate 7; the floating element sensitive chip 8 is the sensitive component of the wall shear stress sensor; the floating element sensitive chip 8 is provided with a wall shear stress output interface.

[0055] The folding tether 9 is designed to be spiral and can produce elastic deformation; the folding tether 9 is made of aluminum alloy.

[0056] Specifically, the folded tether 9 is used to connect the floating element sensitive chip 8 to the fixed end of the floating element and provide restoring force. The design of the folded tether 9 reduces temperature sensitivity by allowing axial strain and reducing the bending degree of the tether, which can prevent the folded tether 9 from bending due to thermal expansion caused by high temperature, thereby widening the operating temperature range of the wall shear stress sensor.

[0057] During the calibration process, the relative sliding between the mass block 5 and the floating element sensitive chip 8 is observed in real time through a zoom camera. If relative sliding occurs between the two, when the force measured by the calibrated wall shear stress sensor is in the range of 0.1-300 Pa, the mass of the mass block 5 is increased to ensure that relative sliding does not occur between the mass block 5 and the floating element sensitive chip 8.

[0058] A rubber pad 6 with a first thickness is adhered to the lower end of the mass block 5, and the rubber pad 6 is in direct contact with the upper surface of the floating element. During the calibration process, the relative sliding between the mass block 5 and the sensitive chip 8 of the floating element is observed in real time through a zoom camera. If relative sliding occurs between the two, when the force range measured by the calibrated wall shear stress sensor is between 300-500Pa, the roughness of the rubber pad 6 adhered under the mass block 5 is increased to ensure that no relative sliding occurs between the mass block 5 and the sensitive chip 8 of the floating element.

[0059] Specifically, because the floating element sensitive chip 8 is relatively thin (300-350 μm), the weight of the mass block 5 it can withstand cannot be too great. Therefore, when the force range measured by the calibrated wall shear stress sensor is between 0.1 and 300 Pa, the mass of the mass block 5 is increased to prevent relative sliding between the mass block 5 and the floating element sensitive chip 8. The surface of the sensitive chip is relatively smooth, with a low roughness of 0.3-0.4 nm. To meet the requirements of a large calibration range, a thin and lightweight rubber pad 6 (approximately 10 μm thick) is attached beneath the mass block 5 to increase the friction coefficient of the contact surface. When the force range measured by the calibrated wall shear stress sensor is between 300 and 500 Pa, the roughness of the rubber pad 6 attached beneath the mass block 5 is increased to prevent relative sliding between the mass block 5 and the floating element sensitive chip 8.

[0060] To avoid damaging the calibrated wall shear stress sensor, the target force output by the motorized precision translation stage 1 must not exceed the maximum range of the calibrated wall shear stress sensor. For example, if the calibrated wall shear stress sensor has a range of 0.1-500 Pa, the target force set by the motorized precision translation stage 1 should not exceed 500 Pa.

[0061] During calibration, the calibration device including the electric precision translation stage 1, the flexible flexure rod 3 assembly, the micro-force probe 4, the mass block 5, and the floating element is installed on the vibration isolation table. An organic glass shell is set outside the calibration device and the vibration isolation table to reduce the influence of vibration and air circulation.

[0062] S2. Control the electric precision displacement stage 1 to generate the target force, measure the displacement of the micro-force probe 4, obtain the deformation of the flexible flexible rod 3 based on the displacement of the electric precision displacement stage 1 and the displacement of the micro-force probe 4, and then obtain the force F exerted on the flexible flexible rod 3; calculate the wall shear stress of the floating element transmitted by the mass block 5 to the floating element based on the force F exerted on the flexible flexible rod 3 and the contact area between the mass block 5 and the floating element.

[0063] The calibration system also includes a laser interferometer 10, which is used to measure the displacement x2 of the micro-force probe 4. In one embodiment of the present invention, a Renishaw XL80 laser interferometer 10 is used to measure the displacement of the micro-force probe 4. When the motorized precision translation stage 1 generates a displacement x1 through software drive, the corresponding target force output can be obtained on the motorized precision translation stage 1.

[0064] The calculation formula of the deformation variable Δx of the flexible rod 3 is:

[0065] Δx=x2-x1

[0066] Wherein, x2 is the displacement of the micro-force probe 4 , and x1 is the displacement of the electric precision translation stage 1 .

[0067] The force F generated by the flexible flexible rod 3 is calculated based on the stiffness k of the flexible flexible rod 3 and the deformation of the flexible flexible rod 3. The calculation formula is:

[0068] F = k·(x2-x1).

[0069] Specifically, the electric precision displacement stage 1 is driven by software to generate a displacement x1, causing the flexible flexible rod 3 to deform. At this time, the flexible flexible rod 3 drives the free end of the micro-force probe 4 to transfer force to the mass block 5. Since the lower end of the mass block 5 is attached with a rubber pad 6, which has a sufficiently large friction coefficient, there is no relative displacement between the mass block 5 and the floating element sensitive chip 8. The mass block 5 drives the floating element sensitive chip 8 to change its displacement through static friction. Due to the elastic deformation of the floating element folding tether 9, the position of the micro-force probe 4 will also be displaced. Due to the special structure of this calibration device, the tail of the flexible flexible rod 3 is consistent with the displacement deformation generated by the micro-force probe 4. Therefore, the deformation variable Δx of the flexible flexible rod 3 can be obtained by subtracting the displacement x1 generated by the electric precision displacement stage 1 from the displacement x2 of the micro-force probe 4 measured by the laser interferometer 10. The force value F generated by the flexible flexible rod 3 is:

[0070] F=kΔx=k(x2-x1),

[0071] Wherein, k is the stiffness of the flexible rod 3.

[0072] In a specific embodiment of the present invention, the force value τ that causes the floating element sensitive chip 8 to change in displacement is W It is the static friction force f between the mass block 5 and the floating element sensitive chip 8 . Based on Newton's third law, the static friction force f is equal to the force F generated by the flexible flexible rod 3 .

[0073] S3. Obtain a first error between the target force and the wall shear stress transmitted to the floating element by the mass block 5; if the first error exceeds the allowable range, adjust the position where the free end of the micro-force probe 4 contacts the side surface of the mass block 5 until the error is within the allowable range.

[0074] It is known that the area of ​​the sensitive part of the floating element sensitive chip 8 is S, and the wall shear stress τ transmitted by the mass block 5 to the floating element sensitive chip 8 is W The force F generated by the flexible rod 3 has the following relationship:

[0075]

[0076] Because the target force is measured in Pa, the area S of the sensitive portion of the floating element's sensitive chip 8 is designed to be identical to the bottom area of ​​the mass 5. The entire sensitive portion of the floating element's sensitive chip 8 is in contact with the bottom of the mass 5. The calibration value of S ensures that the force measured by the wall shear stress sensor is equal to the target force when there is no measurement error. The target force generated and measured by this calibration device are traceable to international units.

[0077] The computer obtains the displacement x2 of the micro-force probe 4, the displacement x1 of the electric precision translation stage 1, and the deformation Δx of the flexible flexible rod 3. Based on the stiffness k of the flexible flexible rod 3, the force F generated by the flexible flexible rod 3 is calculated. The force F is then divided by the bottom area S of the mass block 5 to obtain the wall shear stress τ transmitted by the mass block 5 to the floating element sensitive chip 8. W , τ W The first error is obtained by taking the absolute value after subtracting it from the target force.

[0078] If the first error exceeds the allowable range, the contact position between the free end of the micro-force probe 4 and the side surface of the mass block 5 is adjusted so that the lowest point of the free end of the micro-force probe 4 is located directly below the center point of the side surface of the mass block 5 .

[0079] Specifically, by adjusting the position where the free end of the micro-force probe 4 contacts the side surface of the mass block 5 so that it is located directly below the center point, the force value transmitted by the flexible flexible rod 3 through the micro-force probe 4 can be smoothly and accurately transmitted to the mass block 5, thereby more realistically reflecting the magnitude of the wall shear stress.

[0080] S4. Determine whether the calibrated wall shear stress sensor is qualified based on the target force generated by the electric precision translation stage 1 and the force measured by the calibrated wall shear stress sensor.

[0081] Judging whether the calibrated wall shear stress sensor is qualified according to the target force generated by the electric precision translation stage 1 and the force measured by the calibrated wall shear stress sensor includes:

[0082] Step 1: The electric precision translation stage 1 generates a target force, with the deformation variable Δx of the flexible rod 3 as the abscissa and the force measured by the calibrated wall shear stress sensor as the ordinate, to form a measurement point.

[0083] Step 2: Repeatedly apply multiple different target forces and record the deformation Δx of the corresponding flexible rod 3 and the force measured by the calibrated wall shear stress sensor to form multiple measurement points;

[0084] Step 3: Fit the multiple measurement points into a second straight line; using different target forces output by the electric precision translation stage 1 as the ordinate and the deformation variable Δx of the corresponding flexible flexure 3 as the abscissa to form multiple target points, and fitting the multiple target points into a first straight line;

[0085] Step 4: Within the measuring range of the calibrated wall shear stress sensor, determine the maximum value of the difference between the measured force and the target force generated by the deformation Δx of the flexible rod 3 corresponding to the same direction on the second straight line and the first straight line. Divide the maximum value of the difference between the measured force and the target force by the difference between the upper and lower limits of the measuring range of the calibrated wall shear stress sensor to obtain the linear error.

[0086] Step 5: Determine whether the calibrated wall shear stress sensor is qualified based on whether the linear error is within the nominal accuracy range of the calibrated wall shear stress sensor.

[0087] Specifically, to avoid damaging the calibrated wall shear stress sensor, the target force set by the electric precision translation stage 1 cannot exceed the upper limit of the range of the calibrated wall shear stress sensor. For example, if the range of the calibrated wall shear stress sensor is 0.1-500Pa, the target force set by the electric precision translation stage 1 should not exceed 500Pa. In a specific embodiment of the present invention, relatively dispersed target points are selected during linear fitting to make the fitted line more accurate. The electric precision translation stage 1 outputs different target forces, such as 0Pa, 100Pa, 200Pa, 300Pa, 400Pa, and 500Pa.

[0088] The wall shear stress actually measured by the calibrated wall shear stress sensor is ultimately output to the computer via the output interface of the floating element sensor chip 8. The target force generated by the motorized precision translation stage 1 is also output to the computer. The computer combines the deformation Δx of the flexible rod 3 to determine the target point and the measurement point. The computer then fits the second straight line to the first straight line, ultimately determining the linear error.

[0089] Compared to the prior art, the calibration method provided in this embodiment generates a target force from an electric precision displacement stage 1. This target force is then transmitted to a flexible rod, which then deforms to transmit the target force to a mass 5. The force generated and transmitted in this process is stable. Based on the main structure of the flexible rod, the displacement of the micro-force probe 4 is measured by a laser interferometer 10 to precisely measure the displacement of the flexible rod's tail, ensuring accurate force readings and meeting high-precision requirements. The design of the micro-force probe 4 accommodates the compact size of the floating element's sensitive chip 8 and enables force transmission. The calibration method in this embodiment generates a stable target force with micro-nanon-level accuracy, and a measurement uncertainty of U = 0.06% at a confidence factor of k = 2. The mass 5 is attached to a rubber pad 6. By varying the roughness of the rubber pad 6 or the mass of the mass 5, the measuring range can be increased without sacrificing measurement accuracy. The calibrated wall shear stress range is 0.1-500 Pa, with a repeatability error better than 0.5%, an accuracy better than 0.2%, and a maximum force resolution better than 0.1 Pa. By fitting multiple measurement points to a second straight line and multiple target force points to a first straight line to calculate linear error, the calibration process is completed quickly with a short response time. By fixing the entire calibration device on a vibration isolation table and shielding it with a plexiglass enclosure, the effects of vibration and air circulation are minimized, ensuring stable environmental conditions. Therefore, the present invention has relatively relaxed measurement environment requirements and can achieve high-precision calibration in complex environments.

[0090] Those skilled in the art will appreciate that all or part of the process steps of the above-described embodiments can be implemented by instructing related hardware through a computer program, and the program can be stored in a computer-readable storage medium, such as a magnetic disk, an optical disk, a read-only memory, or a random access memory.

[0091] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A static calibration method for a floating element wall shear stress sensor, characterized in that: The method comprises: fixing one end of a flexible flexure rod assembly on an electric precision displacement stage; fixing the free end of the flexible flexure rod assembly to the fixed end of a micro-force probe, wherein the free end of the micro-force probe contacts the side surface of a mass block to achieve force transmission; contacting the mass block with a sensitive chip of a floating element without relative sliding, so that the mass block transmits force to the floating element through static friction; and the floating element senses the magnitude of the force and outputs the force to be measured by a calibrated wall shear stress sensor. The electric precision translation stage is controlled to generate a target force, and the displacement of the micro-force probe is measured. The deformation of the flexible rod is obtained based on the displacement of the electric precision translation stage and the displacement of the micro-force probe, and the force F acting on the flexible rod is further obtained. The wall shear stress of the floating element transmitted by the mass block to the floating element is calculated based on the force F acting on the flexible rod and the contact area between the mass block and the floating element. Obtaining a first error between the target force and the wall shear stress transmitted by the mass block to the floating element; if the first error exceeds an allowable range, adjusting the contact position between the free end of the micro-force probe and the side surface of the mass block until the error is within the allowable range; Whether the calibrated wall shear stress sensor is qualified is judged according to the target force generated by the electric precision translation stage and the force measured by the calibrated wall shear stress sensor.

2. The static calibration method according to claim 1, characterized in that: The calculation formula of the deformation variable Δx of the flexible rod is: Δx=x2-x1 Where x2 is the displacement of the micro-force probe, and x1 is the displacement of the electric precision translation stage.

3. The static calibration method according to claim 2, characterized in that: The force F generated by the flexible flexure is calculated based on the stiffness k and the deformation of the flexible flexure. The calculation formula is: F = k·(x2-x1).

4. The static calibration method according to claim 1, characterized in that: If the first error exceeds the allowable range, the contact position between the free end of the micro-force probe and the side surface of the mass block is adjusted so that the lowest point of the free end of the micro-force probe is directly below the center point of the side surface of the mass block.

5. The static calibration method according to claim 1, characterized in that: During the calibration process, the relative sliding between the mass block and the floating element sensitive chip is observed in real time through a zoom camera. If relative sliding occurs between the two, when the force measured by the calibrated wall shear stress sensor is in the range of 0.1-300Pa, the mass of the mass block is increased to ensure that no relative sliding occurs between the mass block and the floating element sensitive chip.

6. The static calibration method according to claim 5, characterized in that: A rubber pad having a first thickness is adhered to the lower end of the mass block, and the rubber pad is in direct contact with the upper surface of the floating element. During the calibration process, the relative sliding between the mass block and the sensitive chip of the floating element is observed in real time through a zoom camera. If relative sliding occurs between the two, and when the force measured by the calibrated wall shear stress sensor is in the range of 300-500 Pa, the roughness of the rubber pad adhered under the mass block is increased to ensure that relative sliding does not occur between the mass block and the sensitive chip of the floating element.

7. The static calibration method according to claim 1, characterized in that: Determining whether the calibrated wall shear stress sensor is qualified according to the target force generated by the electric precision translation stage and the force measured by the calibrated wall shear stress sensor includes: Step 1: A target force generated by the electric precision translation stage is used as the horizontal coordinate, with the deformation variable Δx of the flexible flexure as the horizontal coordinate and the force measured by the calibrated wall shear stress sensor as the vertical coordinate to form a measurement point; Step 2: Repeatedly apply multiple different target forces and record the deformation Δx of the corresponding flexible rod and the force measured by the calibrated wall shear stress sensor to form multiple measurement points; Step 3: Fitting the multiple measurement points into a second straight line; using different target forces output by the electric precision translation stage as the ordinate and the deformation variable Δx of the corresponding flexible flexure as the abscissa to form multiple target points, and fitting the multiple target points into a first straight line; Step 4: Within the measuring range of the calibrated wall shear stress sensor, determine the maximum value of the difference between the measured force and the target force generated by the deformation Δx of the corresponding flexible rod on the second straight line and the first straight line. Divide the maximum value of the difference between the measured force and the target force by the difference between the upper and lower limits of the measuring range of the calibrated wall shear stress sensor to obtain the linear error. Step 5: Determine whether the calibrated wall shear stress sensor is qualified based on whether the linear error is within the nominal accuracy range of the calibrated wall shear stress sensor.

8. The static calibration method according to claim 1, characterized in that: The floating element includes a fixed end and a movable end; the fixed end is a U-shaped silicon substrate, and the movable end is a floating element sensitive chip. Folding tethers are symmetrically arranged on both sides of the floating element sensitive chip and fixedly connected to the inner side walls of the left and right ends of the silicon substrate; the floating element sensitive chip is the sensitive component of the wall shear stress sensor; the floating element sensitive chip is provided with a wall shear stress output interface.

9. The static calibration method according to claim 8, characterized in that: The folding tether is designed in a spiral shape and can produce elastic deformation; the folding tether is made of aluminum alloy.

10. The static calibration method according to any one of claims 1 to 9, characterized in that: During calibration, the calibration device including the electric precision translation stage, flexible flexure rod assembly, micro-force probe, mass block, and floating element is installed on the vibration isolation table. An organic glass shell is set outside the calibration device and the vibration isolation table to reduce the influence of vibration and air circulation.

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