Piezoresistive accelerometer rigidity measuring device based on balance method

Abstract

The invention relates to the technical field of sensor measuring devices, and discloses a piezoresistive accelerometer rigidity measuring device based on a balance method, and the device comprises a pressing mechanism which is disposed on an external optical platform, and is used for driving other structural members to carry out the pressing operation; the acquisition mechanism is mounted on the external optical platform and used for acquiring experimental data, the pressing mechanism comprises a six-axis displacement table and a probe assembly, the bottom of the six-axis displacement table is mounted at the top of the external optical platform, the top of the six-axis displacement table is rotatably connected with a cross beam, and the probe assembly is mounted at the bottom of the cross beam. The measuring probe is composed of the ruby ball head probe and the cantilever-like mounting seat, meanwhile, the cross-shaped scribed line used for measurement of the laser interferometer is designed on the mounting seat, and the material characteristics of the ruby ball head probe made of stainless steel are combined, so that the problem that the measurement precision is influenced by stress deformation of the probe in the measurement process is solved, and the measurement accuracy is improved. And the precision and the accuracy of displacement measurement are greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sensor measuring devices, and particularly to a piezoresistive accelerometer stiffness measuring device based on the balance method. Background Art

[0002] In modern industrial production and scientific research, piezoresistive accelerometers, as key sensors, are widely used in many fields such as aerospace, automotive manufacturing, and seismic monitoring. The research on the stiffness characteristics of accelerometers directly affects the accuracy and reliability of the measurement results of accelerometers and the stability of the operation of related equipment and systems. Therefore, accurately measuring the stiffness of piezoresistive accelerometers is an important prerequisite to ensure their stable operation under various complex working conditions.

[0003] Currently, the more commonly used methods for measuring the stiffness of piezoresistive accelerometers are the static force loading method and the dynamic excitation method. The static force loading method measures the deformation of the accelerometer by applying a constant external force to the accelerometer, records the external force and the strain generated by the accelerometer to calculate the stiffness. This method has a simple principle, but requires complex mechanical devices to control the magnitude and method of the external force, and is easily affected by factors such as friction and the elastic deformation of the device itself during the loading process, resulting in large measurement errors and difficult to meet the high-precision measurement requirements. The dynamic excitation method is to apply a dynamic excitation signal to the accelerometer, such as a sine wave or a pulse signal, etc., and calculate the stiffness by analyzing the response signal of the accelerometer and combining relevant dynamic models. However, this method is easily affected by factors such as external vibration and electromagnetic signals, and it is difficult to accurately establish the dynamic model of the system, and the error of the model will also affect the final measurement accuracy, making it difficult to meet the daily measurement requirements. Therefore, the present invention provides a piezoresistive accelerometer stiffness measuring device based on the balance method to solve the deficiencies existing in the prior art. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention provides a piezoresistive accelerometer stiffness measuring device based on the balance method, which solves the problem of insufficient accuracy of the existing piezoresistive accelerometer stiffness measurement method.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A piezoresistive accelerometer stiffness measuring device based on the balance method, comprising:

[0006] A downward pressing mechanism: which is installed on an external optical platform and is used to drive other structural components to perform downward pressing operations;

[0007] A collection mechanism: which is installed on an external optical platform and is used to obtain experimental data.

[0008] Preferably, the pressing mechanism includes a six-axis displacement stage and a probe assembly. The bottom of the six-axis displacement stage is mounted on the top of an external optical platform, and a cross beam is rotatably connected to the top of the six-axis displacement stage.

[0009] Preferably, the probe assembly is mounted on the bottom of the cross beam. The probe assembly includes a nano micro-stage and a probe group. The top of the nano micro-stage is fixedly connected to the bottom of the cross beam. The probe group includes a mounting seat and a ruby ball head probe. The top of the mounting seat is fixedly connected to the bottom of the nano micro-stage, and the ruby ball head probe is mounted on the bottom of the mounting seat.

[0010] Preferably, the acquisition mechanism includes a bottom acquisition component and a top acquisition component. The bottom acquisition component includes a precision balance and two brackets I. The precision balance and the two brackets I are both placed on the top of the optical platform.

[0011] Preferably, an accelerometer base is fixedly connected to the top of the precision balance, and a camera is installed inside the bracket I.

[0012] Preferably, the top acquisition component includes a bracket II. The bottom of the bracket II is fixedly connected to the top of the external optical platform. An instrument displacement stage is fixedly connected to the bottom of the bracket II, and a laser interferometer is installed at the bottom of the instrument displacement stage.

[0013] Preferably, the ruby ball head probe is located directly above the accelerometer base.

[0014] A piezoresistive accelerometer stiffness measurement system based on the balance method is applied to the piezoresistive accelerometer stiffness measurement device described in any one of the above. The system includes a host computer processing module, which is used to electrically connect the precision balance and the laser interferometer to process the collected data.

[0015] The present invention provides a piezoresistive accelerometer stiffness measurement device based on the balance method.

[0016] It has the following beneficial effects:

[0017] 1. In the present invention, a measurement probe composed of a ruby ball head probe and a cantilever beam-like mounting seat is used. At the same time, a cross scale for laser interferometer measurement is designed on the mounting seat. Combining with the material characteristics of the ruby ball head probe made of stainless steel, the problem that the force deformation of the probe affects the measurement accuracy during the measurement process is solved, and the accuracy and accuracy of displacement measurement are greatly improved.

[0018] 2. The present invention realizes automatic adjustment of the threshold and switching of the sampling rate according to the data characteristics through a dynamic threshold detection algorithm that combines the sliding window mean-standard deviation method and the CUSUM algorithm, reduces the amount of data, improves the data utilization rate, and makes the finally calculated result more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a perspective view of the present invention;

[0020] Figure 2 is a schematic structural view of the mounting base of the present invention;

[0021] Figure 3 is a flowchart of the working steps of the present invention;

[0022] Figure 4 is a flowchart of the stiffness measurement of the piezoresistive accelerometer of the present invention.

[0023] Among them, 1. Precision balance; 2. Nano micro stage; 3. Laser interferometer; 4. Probe group; 5. Six-axis displacement stage; 6. Cross beam; 7. Accelerometer base; 8. Camera; 9. Support one; 10. Instrument displacement stage; 11. Support two; 12. Mounting base; 13. Ruby ball head probe. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0025] Please refer to the attached Figure 1 - attached Figure 2 , the embodiments of the present invention provide a piezoresistive accelerometer stiffness measurement device based on the balance method, including:

[0026] Pressing mechanism: It is installed on an external optical platform and is used to drive other structural components to perform pressing operations. The optical platform is a conventional tabletop for experiments and is used to place and install experimental equipment. The pressing mechanism includes a six-axis displacement stage 5 and a probe assembly. The bottom of the six-axis displacement stage 5 is installed on the top of the external optical platform. The top of the six-axis displacement stage 5 is rotatably connected to a cross beam 6. The cross beam 6 serves to connect the probe assembly. The probe assembly is installed at the bottom of the cross beam 6. The probe assembly includes a nano micro stage 2 and a probe group 4. The probe assembly is used to directly contact the surface of the accelerometer to obtain corresponding data. The top of the nano micro stage 2 is fixedly connected to the bottom of the cross beam 6. The probe group 4 includes a mounting base 12 and a ruby ball head probe 13. The top of the mounting base 12 is fixedly connected to the bottom of the nano micro stage 2. The ruby ball head probe 13 is installed at the bottom of the mounting base 12.

[0027] Data acquisition mechanism: It is installed on the external optical platform and is used to acquire experimental data. The data acquisition mechanism includes a bottom-layer acquisition component and a top-layer acquisition component. The bottom-layer acquisition component includes a precision balance 1 and two supports 9. The precision balance 1 and the two supports 9 are both placed on the top of the optical platform. The top of the precision balance 1 is fixedly connected to an accelerometer base 7. The accelerometer is placed inside the accelerometer base 7. A camera 8 is installed inside the support 9. Two groups of cameras 8 monitor the experimental process from different angles. The top-layer acquisition component includes a support 11. The bottom of the support 11 is fixedly connected to the top of the external optical platform. The bottom of the support 11 is fixedly connected to an instrument displacement stage 10. A laser interferometer 3 is installed at the bottom of the instrument displacement stage 10. The ruby ball head probe 13 is located directly above the accelerometer base 7.

[0028] Please refer to the attached Figure 3 - attached Figure 4 , an embodiment of the present invention provides a piezoresistive accelerometer stiffness measurement system based on the balance method, including a host computer processing module. The host computer processing module is used to electrically connect the precision balance 1 and the laser interferometer 3, process the acquired data, perform corresponding calculations on the acquired data using the CUSUM algorithm and the least squares method, etc., and finally obtain the test data.

[0029] Specifically, first, an experimental probe is designed. The probe group 4 consists of a mounting base 12 and a ruby ball probe 13. The mounting base 12 is used to connect the nano-micro stage 2 and the ruby ball probe 13. To facilitate the measurement of the displacement at the top of the ruby ball probe 13, the mounting base 12 is designed in the shape of a cantilever beam. The ruby ball probe 13 is installed at the end of the cantilever beam. At the installation position of the ruby probe at the free end of the cantilever beam, cross-hairs for alignment are designed to facilitate the measurement of displacement in the later stage. During the actual measurement process, the designed length of the cantilever beam is 10 mm. Under the action of force, the probe base will produce flexural deformation, which will deflect the direction of the ruby ball probe 13 and affect the accuracy of displacement measurement. To reduce the influence of the flexural deformation of the mounting base 12 on the measurement, a wing plate structure is designed on the basis of the cantilever beam, which greatly improves the stiffness of the mounting base 12 and reduces the influence of flexural deformation on the measurement. The shape of the cantilever beam after adding the wing plate is a trapezoid with an upper side of 2 mm, a lower side of 28 mm, and a height of 10 mm. The connection part between the mounting base 12 and the nano-micro stage 2 is a rectangle with a side length of 28 mm, and through holes for bolt fixation are provided at the four corners. The thickness of the mounting base 12 is designed to be 3.5 mm. To facilitate turning processing, the material of the probe base is selected as aluminum alloy. The ruby ball probe 13 is selected as the probe part, and the corresponding size of the ruby ball probe 13 can be replaced according to the size of the sensitive unit of the accelerometer to be measured. The material of the ruby ball probe 13 is tungsten steel and ruby, with extremely high hardness, ensuring that no deformation will occur during downward pressure to affect the displacement measurement, and the ruby ball is spherical, which can greatly reduce the stress distribution during the experiment and avoid damage to the accelerometer. Then, the device is built. The whole device is mainly divided into three parts: a downward pressure module, a data acquisition module, and a host computer processing module. The downward pressure module consists of a six-axis displacement stage 5, a cross beam 6, a nano-micro stage 2, and a probe assembly. The six-axis displacement stage 5 is used to roughly adjust the position of the probe, and the nano-micro stage 2 is used to finely adjust the position of the probe and is also responsible for controlling the entire downward pressure process.The data acquisition module consists of a precision balance 1, an accelerometer base 7, and a laser interferometer 3. The accelerometer is fixedly connected to the precision balance 1 through an adapter. The laser interferometer 3 is used to measure the displacement at the top of the ruby ball probe 13. Both the precision balance 1 and the laser interferometer 3 are electrically connected to the upper computer processing module for convenient data acquisition and transmission. Then, adjust the probe position and control the nano-micromotion stage 2 to press down on the accelerometer, and collect the experimental data of the precision balance 1 and the laser interferometer 3. After setting up the device, first, it is necessary to adjust the relative position between the probe and the accelerometer to ensure that the position where the probe presses down is the geometric center of the sensitive unit on the surface of the accelerometer, and the probe just touches the surface of the sensitive unit. Subsequently, control the nano-micromotion stage 2 to continuously press down three times at a certain step interval of 10 seconds. After the readings are stable, continuously lift it three times at the same step and time interval, and collect the data of the precision balance 1 and the laser interferometer 3. Then, implement dynamic data acquisition based on a dynamic threshold detection algorithm that combines the sliding window mean-standard deviation method and the CUSUM algorithm. During the acquisition process, use the sliding window mean-standard deviation method to detect the fluctuations of the real-time acquired original signal, set the window size. When data acquisition starts, update the window mean and standard deviation in real-time according to the data within the window, calculate the window fluctuation index based on the ratio of the standard deviation to the mean. When the fluctuation index exceeds the threshold, it is determined that the readings of the laser interferometer 3 and the precision balance 1 are unstable, and the sampling frequency is reduced; when the fluctuation index is lower than the threshold, it is determined that the readings of the laser interferometer 3 and the precision balance 1 are stable, and the sampling frequency is increased. To avoid sampling frequency switching caused by noise fluctuations, use the CUSUM algorithm to detect the mean shift. The CUSUM algorithm can quickly identify small but continuous changes during the acquisition process by accumulating the deviation between the observed value and the target mean. When the mean-standard deviation method detects a state change, use the CUSUM algorithm to observe the shift of the window mean in real-time to avoid sampling frequency switching caused by noise fluctuations. Set the window size s. When data acquisition starts, update the mean μ and standard deviation σ of the data within the window in real-time according to the data within the window. Then calculate the fluctuation index of the data within the window:

[0030]

[0031] When the fluctuation index exceeds the threshold θ max , use the CUSUM algorithm to observe the shift of the window mean in real-time. Set the mean within the current window as the target mean μ0, and set the tolerance deviation k and the alarm threshold h. For the data ω of the laser interferometer 3 collected next t , calculate the detection of positive shift and negative shift

[0032]

[0033] If or then it is determined that the data is unstable, and the sampling frequency is reduced to f min At the same time, update μ0 and k. When the fluctuation index is lower than the threshold θ min , use the CUSUM algorithm to observe the shift of the mean value of the observation window. When the detection state changes from or to or it is determined that the data is stable, and the sampling frequency is increased to f max At the same time, update μ0 and k; then preprocess the experimental data, filter the data collected by the laser interferometer 3 in the high-speed acquisition mode, and then calculate the pressure F = mg received by the accelerometer according to the data m collected by the precision balance 1, and construct the force value and the corresponding displacement value ω (the preprocessed data of the laser interferometer 3) into a data group (ω i , F i ), where i = 1, 2,..., n; then fit the stiffness of the piezoresistive accelerometer. The calculation formula for the stiffness of the sensitive element of the accelerometer is:

[0034]

[0035] For the preprocessed data group (ω i , F i )(where i = 1, 2,..., n), use the least squares method to fit the stiffness. Assume that the stiffness straight line equation is:

[0036] F = kω + b;

[0037] For each data point, the distance from it to the straight line is:

[0038] d i = F i - (kω i - b);

[0039] The least squares method requires that the sum of the squares of the distances from all data points to the straight line reaches the minimum value. Solve the minimum value of the sum of squares function to find the slope of the stiffness straight line equation when the function reaches the minimum value. Therefore, the stiffness k of the sensitive element of the accelerometer is fitted, and the expression is:

[0040]

[0041] Working principle: First, use the angular displacement stage in the six-axis displacement stage 5 to adjust the angle of the cross beam 6 until the cross beam 6 is in a horizontal state, ensuring that the stepping direction of the nano-micro stage 2 is in the vertical direction. Coarsely adjust the position of the probe to near the accelerometer to be measured with the six-axis displacement stage 5. Then, observe the relative position between the probe and the accelerometer through the camera 8, and adjust the six-axis displacement stage 5 to ensure that the pressing position of the probe is at the geometric center of the sensitive unit of the accelerometer. Then, finely adjust the position of the probe with the nano-micro stage 2 to ensure that the probe just touches the sensitive unit of the accelerometer to be measured. Next, adjust the instrument displacement stage 10 where the laser interferometer 3 is installed to adjust the measurement position of the laser interferometer 3, and adjust the laser red dot of the laser interferometer 3 to the crosshair of the probe base. Subsequently, adjust the signal intensity, and repeat the above operations until the working requirements of the laser interferometer 3 are met. Then, control the nano-micro stage 2 to continuously press down three times at a certain step interval of 10 seconds. After the readings are stable, continuously lift up three times at the same step and time interval. Subsequently, repeat the above pressing operation to achieve multiple measurements. During the process of controlling the nano-micro stage 2 to press down, the readings of the precision balance 1 and the laser interferometer 3 are collected in real time, transmitted to the host computer processing system for storage, and then algorithm calculations are performed. Finally, the value of the stiffness of the accelerometer is obtained.

[0042] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A piezoresistive accelerometer stiffness measurement device based on the balance method, characterized in that Including: A pressing mechanism: It is installed on an external optical platform and is used to drive other structural components for pressing operations. A data acquisition mechanism: It is installed on an external optical platform and is used to obtain experimental data.

2. The piezoresistive accelerometer stiffness measurement device based on the balance method according to claim 1, characterized in that, The pressing mechanism includes a six-axis displacement stage (5) and a probe assembly. The bottom of the six-axis displacement stage (5) is installed on the top of the external optical platform, and a cross beam (6) is rotatably connected to the top of the six-axis displacement stage (5).

3. The piezoresistive accelerometer stiffness measurement device based on the balance method according to claim 2, wherein The probe assembly is installed at the bottom of the cross beam (6). The probe assembly includes a nano-micro stage (2) and a probe group (4). The top of the nano-micro stage (2) is fixedly connected to the bottom of the cross beam (6). The probe group (4) includes a mounting base (12) and a ruby ball probe (13). The top of the mounting base (12) is fixedly connected to the bottom of the nano-micro stage (2), and the ruby ball probe (13) is installed at the bottom of the mounting base (12).

4. The piezoresistive accelerometer stiffness measurement device based on the balance method according to claim 3, characterized in that, The data acquisition mechanism includes a bottom-layer acquisition component and a top-layer acquisition component. The bottom-layer acquisition component includes a precision balance (1) and two supports one (9). The precision balance (1) and the two supports one (9) are both placed on the top of the optical platform.

5. The piezoresistive accelerometer stiffness measurement device based on the balance method according to claim 4, characterized in that, The top of the precision balance (1) is fixedly connected to an accelerometer base (7), and a camera (8) is installed inside the support one (9).

6. The piezoresistive accelerometer stiffness measurement device based on the balance method according to claim 4, characterized in that The top-layer acquisition component includes a support two (11). The bottom of the support two (11) is fixedly connected to the top of the external optical platform. An instrument displacement stage (10) is fixedly connected to the bottom of the support two (11), and a laser interferometer (3) is installed at the bottom of the instrument displacement stage (10).

7. The piezoresistive accelerometer stiffness measurement device based on the balance method according to claim 5, characterized in that The ruby ball probe (13) is located directly above the accelerometer base (7).

8. A piezoresistive accelerometer stiffness measurement system based on the balance method, applied to a piezoresistive accelerometer stiffness measurement device according to any one of claims 1-7, characterized in that, Including a host computer processing module, which is used to electrically connect the precision balance (1) and the laser interferometer (3) to process the acquired data.

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