Static calibration system for wall shear stress sensor of floating element

Abstract

The invention relates to a static calibration system for a floating element wall surface shear stress sensor. The system comprises an electric precision displacement table, a flexible rod assembly, a micro-force probe, a mass block, a floating element and a signal processing unit, the electric precision displacement table is used for providing target force, and the target force acts on the flexible rod assembly; the flexible rod assembly transmits the received target force to the micro-force probe; the micro-force probe transmits the target force to the floating element through the mass block; the signal processing unit is used for fitting different target forces output by the electric precision displacement table and deformation quantities of the flexible flexible rod corresponding to the target forces into a first straight line, and fitting wall surface shear stresses output by the floating element corresponding to the different target forces and deformation quantity signals of the flexible flexible rod corresponding to the wall surface shear stresses into a second straight line; whether the calibrated wall surface shear stress sensor is qualified or not is judged by judging whether the linear error of the second straight line and the first straight line is within the nominal precision range of the wall surface shear stress sensor or not.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical metrology, and in particular to a static calibration system 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 systematic research on the calibration of wall shear stress sensors, and there is a lack of a static calibration system 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 system for a floating element wall shear stress sensor, so as to solve the problem in the prior art that a static calibration system for a wall shear stress sensor with both high precision and a large range is lacking.

[0005] An embodiment of the present invention provides a static calibration system for a floating element wall shear stress sensor, the calibration system comprising a calibration device; the calibration device comprising: an electric precision translation stage, a flexible flexure rod assembly, a micro-force probe, a mass block, a floating element, and a signal processing unit; the electric precision translation stage is used to provide a target force, the target force acting on the flexible flexure rod assembly, and is also used to output the target force to the signal processing unit;

[0006] The flexible rod assembly transmits the received target force to the micro-force probe; the micro-force probe then transmits the target force to the floating element through the mass block; the floating element senses the target force and outputs the wall shear stress to the signal processing unit;

[0007] The signal processing unit obtains the deformation of the flexible flexible rod based on the displacement of the electric precision translation stage and the displacement of the micro-force probe, and then fits the different target forces output by the electric precision translation stage and the deformation of the flexible flexible rod corresponding to the target forces into a first straight line, and fits the wall shear stress output by the floating element corresponding to the different target forces and the deformation signal of the flexible flexible rod corresponding to the wall shear stress into a second straight line; and determines whether the calibrated wall shear stress sensor is qualified by judging whether the linear error between the second straight line and the first straight line is within the nominal accuracy range of the wall shear stress sensor.

[0008] Furthermore, the flexible flexible rod assembly includes a flexible flexible rod and a fixed bracket. The flexible flexible rod and the fixed bracket are an integrated structure. The upper end of the flexible flexible rod is fixed to the lower surface of the fixed bracket as a fixed end; the lower end of the flexible flexible rod is a free end; one end of the micro-force probe is fixedly connected to the free end of the flexible flexible rod, and the other end is in contact with one side of the mass block; the mass block is placed above the floating element.

[0009] Furthermore, after the electric precision translation stage applies the target force, there is no relative sliding between the mass block and the floating element, and the mass block transmits the force to the floating element through the maximum static friction force.

[0010] 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.

[0011] Furthermore, the folding tether is designed to be spiral and can produce elastic deformation; the folding tether is made of aluminum alloy.

[0012] 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.

[0013] Furthermore, the micro-force probe is a rectangular parallelepiped structure, and the short side of the rectangular parallelepiped is welded to the lower surface of the free end of the flexible flexible rod.

[0014] Furthermore, the static calibration system also includes a laser interferometer, which is used to measure the displacement of the micro-force probe.

[0015] Furthermore, the calculation formula for the deformation variable Δx of the flexible flexure is:

[0016] Δx=x2-x1

[0017] Wherein, x2 is the displacement of the micro-force probe measured by the laser interferometer, and x1 is the displacement of the electric precision translation stage.

[0018] Furthermore, the calibration system also includes a vibration isolation table and an organic glass shell; the calibration device is installed on the vibration isolation table, and the organic glass shell is arranged outside the calibration device and the vibration isolation table.

[0019] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0020] 1. The target force generated by the calibration device of the present invention comes from the electric precision displacement stage. The target force is transmitted to the flexible rod, and the target force is transmitted to the mass block through the deformation of the flexible rod. The force generated and transmitted in this process is stable.

[0021] 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.

[0022] 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.

[0023] 4. The calibration device of the present invention generates 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.

[0024] 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 through a signal processing unit. The calibration process is completed quickly with a short response time.

[0025] 6. To minimize the effects of vibration and air circulation, the entire calibration device is fixedly mounted on a vibration isolation table and shielded with a plexiglass shell 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.

[0026] 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

[0027] 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.

[0028] Figure 1 Schematic diagram of a static calibration system for a floating element wall shear stress sensor.

[0029] Reference numerals:

[0030] 1-Electric precision translation stage;

[0031] 2-Fix bracket;

[0032] 3-Flexible rod;

[0033] 4-Micro force probe;

[0034] 5-mass block;

[0035] 6-Rubber pad;

[0036] 7-Silicon substrate;

[0037] 8-Floating element sensitive chip;

[0038] 9-Folding tether;

[0039] 10-Laser interferometer. DETAILED DESCRIPTION

[0040] 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.

[0041] A specific embodiment of the present invention discloses a static calibration system for a floating element wall shear stress sensor, as shown in the schematic diagram. Figure 1 The calibration system includes a calibration device, which includes: an electric precision translation stage 1, a flexible flexible rod 3 assembly, a micro-force probe 4, a mass block 5, a floating element, and a signal processing unit. The electric precision translation stage 1 is used to provide a target force, which acts on the flexible flexible rod 3 assembly, and is also used to output the target force to the signal processing unit.

[0042] The 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 floating element senses the target force and outputs the wall shear stress to the signal processing unit;

[0043] The signal processing unit obtains 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 fits the different target forces output by the electric precision displacement stage 1 and the deformation of the flexible flexible rod 3 corresponding to the target forces into a first straight line, and fits the wall shear stress output by the floating element corresponding to the different target forces and the deformation signal of the flexible flexible rod 3 corresponding to the wall shear stress into a second straight line; and determines whether the calibrated wall shear stress sensor is qualified by judging whether the linear error between the second straight line and the first straight line is within the nominal accuracy range of the wall shear stress sensor.

[0044] The flexible flexible rod 3 assembly includes a flexible flexible rod 3 and a fixed bracket 2. 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 mass block 5 is placed above the floating element.

[0045] After the electric precision translation stage 1 applies the target force, there is no relative sliding between the mass block 5 and the floating element, and the mass block 5 transmits the force to the floating element through static friction.

[0046] 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.

[0047] Specifically, linear error refers to the difference between the actual measurement result and the theoretical best-fit straight line when using a measuring device. In this embodiment, when calculating the linear error, the maximum difference between the measured force and the target force corresponding to the same deformation Δx of the flexible rod 3 on the second straight line and the first straight line is determined. The maximum difference between the measured force and the target force is then divided by the difference between the upper and lower range limits of the calibrated wall shear stress sensor to obtain the linear error.

[0048] 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 nano-displacement controller should not exceed 500 Pa.

[0049] 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 a restoring force to offset the wall shear stress applied to the floating element. 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.

[0050] The folding tether 9 is designed to be spiral and can produce elastic deformation; the folding tether 9 is made of aluminum alloy.

[0051] 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.

[0052] The micro-force probe 4 is a rectangular parallelepiped structure, and the short side of the rectangular parallelepiped is welded to the lower surface of the free end of the flexible flexible rod 3 .

[0053] The static calibration system further includes a laser interferometer 10 , which is used to measure the displacement of the micro-force probe 4 .

[0054] A specific embodiment of the present invention uses a Renishaw XL80 laser interferometer 10 .

[0055] The calculation formula of the deformation variable Δx of the flexible rod 3 is:

[0056] Δx=x2-x1

[0057] Wherein, x2 is the displacement of the micro-force probe 4 measured by the laser interferometer 10 , and x1 is the displacement of the electric precision translation stage 1 .

[0058] Specifically, the electric precision displacement stage 1 is driven by software to generate a fixed 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 displacement deformation amount generated by the tail of the flexible flexible rod 3 and the micro-force probe 4 is consistent. Therefore, the deformation amount Δx of the flexible flexible rod 3 can be obtained by subtracting the displacement x2 of the micro-force probe 4 measured by the laser interferometer 10 from the fixed displacement x1 generated by the electric precision displacement stage 1. The force value F generated by the flexible flexible rod 3 is:

[0059] F=kΔx=k(x2-x1)

[0060] Wherein, k is the stiffness of the flexible rod 3.

[0061] 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 .

[0062] Since the floating element sensitive chip 8 is relatively thin (300-350μm), the weight of the mass block 5 that it can bear cannot be too large. In addition, the surface of the sensitive chip is relatively smooth with a low roughness (0.3-0.4nm). In order to meet the requirements of the large calibration range, a thin and light rubber pad 6 (thickness of about 10μm) is attached to the bottom of the mass block 5 to increase the friction coefficient of the contact surface. The area of ​​the sensitive part of the floating element sensitive chip 8 is known to be S, and the wall shear stress τ generated by the displacement change of the floating element sensitive chip 8 is W The force F generated by the flexible rod 3 has the following relationship:

[0063]

[0064] Since the unit of the target force is Pa, the area S of the sensitive portion of the floating element sensitive chip 8 is designed to be the same as the bottom area of ​​the mass block. The entire sensitive portion of the floating element sensitive chip 8 is in contact with the bottom of the mass block. The calibration value of S can ensure that the force measured by the wall shear stress sensor is equal to the target force when there is no measurement error.

[0065] The wall shear stress actually measured by the calibrated wall shear stress sensor is then output to the signal processing unit via the output interface of the floating element sensor chip. The target force generated and the measured force by this calibration device are traceable to international units.

[0066] The calibration system further comprises a vibration isolation platform and an organic glass shell; the calibration device is mounted on the vibration isolation platform, and the organic glass shell is arranged outside the calibration device and the vibration isolation platform.

[0067] Compared to the prior art, the calibration device provided in this embodiment generates a target force controlled by a motorized precision translation 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, this embodiment uses a laser interferometer 10 to measure the displacement of a micro-force probe 4 to precisely measure the displacement of the flexible rod's tail, ensuring accurate force measurements and meeting high-precision requirements. This embodiment utilizes the design of the micro-force probe 4 to accommodate the small dimensions of the floating element's sensitive chip 8 and achieve force transmission. The calibration device in this embodiment generates stable target forces with micro-nanon accuracy, and a measurement uncertainty of U = 0.06% at a confidence factor k = 2. The design of the mass 5, with a rubber pad 6 of a first thickness attached, balances a wide range of calibration with high precision. The wall shear stress range capable of calibration is 0.1 to 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. This embodiment uses a signal processing unit to fit multiple measurement points into a second straight line and multiple target forces into a first straight line to calculate linear errors, completing the calibration process quickly and with a short response time. To minimize the effects of vibration and airflow, the entire calibration device is fixedly mounted on a vibration isolation table and shielded with a plexiglass enclosure to ensure stable environmental conditions. Therefore, the measurement environment requirements of this embodiment are relatively relaxed, allowing calibration in complex environments.

[0068] 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.

[0069] 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 system for a floating element wall shear stress sensor, characterized in that: The calibration system includes a calibration device; the calibration device includes: an electric precision translation stage, a flexible flexure rod assembly, a micro-force probe, a mass block, a floating element, and a signal processing unit; the electric precision translation stage is used to provide a target force, the target force acting on the flexible flexure rod assembly, and is also used to output the target force to the signal processing unit; The flexible rod assembly transmits the received target force to the micro-force probe; the micro-force probe then transmits the target force to the floating element through the mass block; the floating element senses the target force and outputs the wall shear stress to the signal processing unit; The signal processing unit obtains the deformation of the flexible flexible rod based on the displacement of the electric precision translation stage and the displacement of the micro-force probe, and then fits the different target forces output by the electric precision translation stage and the deformation of the flexible flexible rod corresponding to the target forces into a first straight line, and fits the wall shear stress output by the floating element corresponding to the different target forces and the deformation signal of the flexible flexible rod corresponding to the wall shear stress into a second straight line; and determines whether the calibrated wall shear stress sensor is qualified by judging whether the linear error between the second straight line and the first straight line is within the nominal accuracy range of the wall shear stress sensor.

2. The static calibration system according to claim 1, characterized in that: The flexible flexible rod assembly includes a flexible flexible rod and a fixed bracket. The flexible flexible rod and the fixed bracket are an integrated structure. The upper end of the flexible flexible rod is fixed to the lower surface of the fixed bracket as a fixed end; the lower end of the flexible flexible rod is a free end; one end of the micro-force probe is fixedly connected to the free end of the flexible flexible rod, and the other end contacts one side of the mass block; the mass block is placed above the floating element.

3. The static calibration system according to claim 2, characterized in that: After the electric precision translation stage applies the target force, there is no relative sliding between the mass block and the floating element, and the mass block transmits the force to the floating element through the maximum static friction force.

4. The static calibration system according to claim 3, 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.

5. The static calibration system according to claim 4, characterized in that: The folding tether is designed to be spiral and can produce elastic deformation; the folding tether is made of aluminum alloy.

6. The static calibration system according to claim 4, characterized in that: 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.

7. The static calibration system according to claim 3, characterized in that: The micro-force probe is a rectangular parallelepiped structure, and the short side of the rectangular parallelepiped is welded to the lower surface of the free end of the flexible flexure rod.

8. The static calibration system according to claim 7, characterized in that: The static calibration system further includes a laser interferometer, which is used to measure the displacement of the micro-force probe.

9. The static calibration system according to claim 8, characterized in that: The calculation formula of the deformation variable Δx of the flexible flexure is: Δx=x2-x1 Wherein, x2 is the displacement of the micro-force probe measured by the laser interferometer, and x1 is the displacement of the electric precision translation stage.

10. The static calibration system according to any one of claims 1 to 7, characterized in that: The calibration system further comprises a vibration isolation platform and an organic glass shell; the calibration device is mounted on the vibration isolation platform, and the organic glass shell is arranged outside the calibration device and the vibration isolation platform.

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