A method and apparatus for doppler laser mode measurement

Abstract

This application provides a Doppler laser mode shape measurement method and apparatus, comprising: S1, calibrating a laser vibrometer; S2, using the laser vibrometer to emit a laser, such that the emitted laser beam is precisely focused and perpendicularly irradiated onto the test point on the surface of the object being measured; S3, acquiring a time-domain vibration displacement signal; S4, preprocessing the time-domain vibration displacement signal, synchronizing the force signal, and acquiring an effective time-domain vibration displacement signal; S5, processing the preprocessed effective time-domain vibration displacement signal to acquire vibration velocity, vibration displacement, and vibration frequency; S6, visualizing the vibration velocity, vibration displacement, and vibration frequency obtained from modal analysis.

Description

Technical Field

[0001] This invention relates to the field of vibration testing technology, specifically to a Doppler laser mode shape measurement method and device. Background Technology

[0002] Modal vibration measurement is a crucial bridge for revealing the true dynamic characteristics of a structure and connecting theoretical models with actual behavior, indispensable for model verification, damage diagnosis, and vibration control. In the field of vibration testing, traditional contact vibration sensors (such as piezoelectric accelerometers) require direct contact with the object being measured, which can affect the vibration characteristics of the object, especially for lightweight, flexible, or high-precision structures, where the drawbacks of contact measurement are more pronounced. Non-contact measurement methods are gradually becoming a research hotspot, among which Doppler laser-based vibration measurement technology has advantages such as high precision, non-contact operation, and fast response speed, showing broad application prospects in modal vibration testing. Summary of the Invention

[0003] The purpose of this invention is to provide a Doppler laser vibration mode measurement method and device to solve the problems of the additional mass effect and inaccuracy of low-frequency measurement caused by existing traditional contact measurement methods. This solves the problem that transmission contact vibration sensors affect the vibration characteristics of the measured object and cannot measure the vibration mode of lightweight, flexible and high-precision structures.

[0004] In a first aspect, this application provides a Doppler laser mode shape measurement method, comprising: S1, calibrate the laser vibration meter; S2, using a laser vibrometer to emit a laser, so that the emitted laser beam is precisely focused and perpendicularly illuminated on the test point on the surface of the object being measured; S3, acquire the time-domain vibration displacement signal; S4 preprocesses the time-domain vibration displacement signal, synchronizes the force signal, and obtains the effective time-domain vibration displacement signal. S5 processes the preprocessed effective time-domain vibration displacement signal to obtain vibration velocity, vibration displacement, and vibration frequency. S6 visualizes the vibration velocity, vibration displacement, and vibration frequency obtained from modal analysis.

[0005] Specifically, S1 includes: Place the standard vibration table in a stable laboratory environment and set the vibration frequency of the standard vibration table to different preset frequency values. Adjust the position of the single-point Doppler laser vibrometer so that its laser beam is perpendicularly irradiated onto the vibrating surface of the standard vibration table; Start the standard vibration table and laser vibrometer, collect acceleration, velocity and displacement data of the standard vibration table at different frequencies, compare and analyze the measurement results of the laser vibrometer with the theoretical values ​​of the standard vibration table, and calibrate if there is a deviation until the measurement results match.

[0006] Specifically, S2 includes: Use a laser vibrometer mounted on the vibrator support frame to emit a laser beam. Adjust the distance between the laser vibrometer and the test point to be greater than or equal to 1 meter. Align the laser emission lens vertically with the test point so that the emitted laser beam is precisely focused and vertically illuminates the test point on the surface of the object being tested.

[0007] Specifically, S3 includes: The laser vibrometer receives the laser signal reflected from the measured point, carrying the vibration information of the measured point. Through its internal photodetector and signal processing circuit, it acquires the raw waveform data of the displacement of the measured point along the laser beam direction over time. The sampling frequency is... Output the time-domain vibration displacement signal at the highest frequency of interest. .

[0008] Specifically, S4 includes: S41: Synchronous acquisition of time-domain vibration displacement signal With input force signal Hardware-triggered synchronization is used to ensure time alignment; S42: Windowing process, applying a Hanning window to the time-domain signal to reduce spectral leakage. , where the window function T is the sampling duration; S43, Overlapping Segmentation, divides the signal into K segments, with each segment having a repetition rate of ≥50%, improving estimation stability.

[0009] Specifically, S5 includes: S51: The vibration displacement signal is obtained by performing bandpass drift compensation integration on the effective time-domain vibration displacement signal. The calculation method is as follows: ; The S52 Fast Fourier Transform (FFT) performs an FFT on each segment of the time-domain signal. , Where k = 1, 2, 3, ... K, Angular frequency; S53 Input Power Spectrum and input-output cross power spectrum Obtain , ; S54: Frequency Response Function (FRF) acquisition, via... Calculate the frequency response function ; S55: Identification of mode shape parameters, using peak extraction method to analyze the FRF amplitude spectrum. Local maxima detection is performed to obtain the vibration frequency. , Where M is the modal order.

[0010] Secondly, this application provides a Doppler laser mode shape measurement device, including a calibration module 201, a laser vibration measurement module 202, an excitation module 203, a sensor module 204, a data acquisition module 205, a data processing module 206, and a data display module 207, wherein: The calibration module 201 is connected to the laser vibration measurement module 202; the laser vibration measurement module 202, the excitation module 203, and the sensor module 204 are all connected to the input terminal of the data acquisition module 205, and the output terminal of the data acquisition module 205 is connected to the data processing module 206 and the data display module 207 in sequence.

[0011] Specifically, calibration module 201 is used to calibrate the measurement accuracy of the laser vibrometer; Laser vibration measurement module 202 is used to emit measurement lasers; Excitation module 203 is used to generate vibration signals; Sensor module 204 is used to collect vibration signals and trigger the data acquisition module to record data; Data acquisition module 205 is used to record vibration signals; The data processing module 206 is used to preprocess the collected vibration signals and convert them into mode physical quantities such as velocity, displacement, and vibration frequency. The data display module 207 is used to visualize and output the data processed by the data processing module.

[0012] Specifically, the calibration frequency of the calibration module 201 includes 256Hz, 200Hz, 160Hz, 100Hz, 80Hz, 60Hz, and 40Hz; the excitation methods of the laser vibration measurement module 202 include a hammer and a vibrator; the sensor module 203 uses both a hammer and a vibrator to excite the structure under test, and the appropriate excitation method is selected according to the actual test requirements. The sensor module 204 includes a laser source, an optical transmitting and receiving system, and a signal processing circuit. The laser source emits a stable laser beam, which is collimated by the optical transmitting system and then irradiates the surface of the object being measured. When the object being measured vibrates, the frequency of the reflected light will shift due to the Doppler effect. The optical receiving system collects the reflected light and interferes with the reference light to generate an interference signal containing vibration velocity information.

[0013] Specifically, the data acquisition module 205 performs real-time acquisition and storage of multi-channel digital signals, and preprocesses the acquired data. The data processing module 206 processes the preprocessed data and converts it into velocity, displacement, and vibration frequency signals. The data display module 207 visualizes the velocity, displacement, and vibration frequency obtained from modal analysis in the form of charts, curves, and three-dimensional models.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a Doppler laser vibration mode measurement method and apparatus. Through a sophisticated hardware system, a powerful software system, and a precise calibration module, it achieves high-precision, non-contact vibration mode testing. The laser vibration measurement module utilizes the Doppler effect for non-contact measurement, avoiding the influence of contact measurement on the vibration characteristics of the measured object. The excitation module provides multiple excitation methods to adapt to different testing needs. The modal analysis module of the software system accurately extracts modal parameters using multiple algorithms. The calibration module ensures the measurement accuracy of the laser vibration meter. This system and method can be widely applied in mechanical engineering, aerospace, and other fields, providing a reliable basis for structural vibration analysis and optimization design. Attached Figure Description

[0015] Figure 1 This is a flowchart of a Doppler laser mode shape measurement method provided by the present invention; Figure 2 This is a diagram illustrating the composition of a Doppler laser mode shape measurement device provided by the present invention. Figure 3 This is a schematic diagram of the laser vibration measurement point according to an embodiment of the present invention; Figure 4 This is a comparison diagram of the vibration displacement of the attached projectile and the connection point in an embodiment of the present invention. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1 like Figure 1 As shown, this embodiment of the invention proposes a Doppler laser mode shape measurement method, including: S1. Calibrate the laser vibrometer. Before measurement, use a standard vibration source to calibrate the laser vibrometer system, determine its sensitivity coefficient and frequency response characteristics, and eliminate systematic errors to ensure measurement accuracy and reliability. In S1, the standard vibration table is placed in a stable laboratory environment, and the vibration frequency of the standard vibration table is set to different preset frequency values ​​(such as 256Hz, 200Hz, etc.). Adjust the position of the single-point Doppler laser vibrometer so that its laser beam is perpendicularly irradiated onto the vibrating surface of the standard vibration table; Start the standard vibration table and laser vibrometer, collect acceleration, velocity and displacement data of the standard vibration table at different frequencies, compare and analyze the measurement results of the laser vibrometer with the theoretical values ​​of the standard vibration table, and calibrate if there is a deviation until the measurement results match.

[0018] S2, use the laser vibrometer mounted on the vibrator support frame to emit a laser, adjust the distance of the laser vibrometer from the test point to 1 meter, and vertically align the laser emission lens with the test point so that the emitted laser beam is precisely focused and vertically irradiates the test point on the surface of the test object. In S2, a laser vibrometer is vertically mounted above the wing model so that the laser beam hits the wing surface vertically. The laser vibration meter is securely mounted on a dedicated support frame, which is firmly fixed to the laser vibration meter.

[0019] S3, Time-Domain Vibration Signal Acquisition: The laser vibrometer receives the laser signal reflected from the measured point, carrying the vibration information of the measured point. Through its internal photodetector and signal processing circuit, it acquires the raw waveform data of the displacement of the measured point along the laser beam direction over time. The sampling frequency is... Output the time-domain vibration displacement signal at the highest frequency of interest. .

[0020] S4 preprocesses the raw waveform data, synchronizes the force signal, and obtains the effective time-domain vibration displacement signal. S41: Synchronous acquisition of time-domain vibration displacement signal With input force signal Hardware-triggered synchronization is used to ensure time alignment; S42: Windowing process, applying a Hanning window to the time-domain signal to reduce spectral leakage. , where the window function T is the sampling duration; S43, Overlapping Segmentation, divides the signal into K segments, with each segment having a repetition rate of ≥50%, improving estimation stability.

[0021] S5 processes the preprocessed effective time-domain vibration signal to obtain vibration velocity, vibration displacement, vibration frequency, etc. Specifically, S5 includes: S51: The vibration displacement signal is obtained by performing bandpass drift compensation integration on the effective time-domain vibration displacement signal. The calculation method is as follows: ; The S52 Fast Fourier Transform (FFT) performs an FFT on each segment of the time-domain signal. , Where k = 1, 2, 3, ... K, Angular frequency; S53 Input Power Spectrum and input-output cross power spectrum Obtain , ; S54: Frequency Response Function (FRF) acquisition, via... Calculate the frequency response function ; S55: Identification of mode shape parameters, using peak extraction method to analyze the FRF amplitude spectrum. Local maxima detection is performed to obtain the vibration frequency. , Where M is the modal order.

[0022] S6 visualizes the velocity, displacement, and vibration frequency results obtained from modal analysis in the form of charts, curves, and 3D models.

[0023] Example 2 This invention provides a Doppler laser mode shape measurement device, comprising a calibration module 201, a laser vibration measurement module 202, an excitation module 203, a sensor module 204, a data acquisition module 205, a data processing module 206, and a data display module 207, wherein: The calibration module 201 is connected to the laser vibration measurement module 202; the laser vibration measurement module 202, the excitation module 203, and the sensor module 204 are all connected to the input terminal of the data acquisition module 205, and the output terminal of the data acquisition module 205 is connected to the data processing module 206 and the data display module 207 in sequence.

[0024] Specifically, calibration module 201 is used to calibrate the measurement accuracy of the laser vibrometer; Laser vibration measurement module 202 is used to emit measurement lasers; Excitation module 203 is used to generate vibration signals; Sensor module 204 is used to collect vibration signals and trigger the data acquisition module to record data; Data acquisition module 205 is used to record vibration signals; The data processing module 206 is used to preprocess the collected vibration signals and convert them into mode physical quantities such as velocity, displacement, and vibration frequency. The data display module 207 is used to visualize and output the data processed by the data processing module.

[0025] Specifically, the calibration frequencies of calibration module 201 include 256Hz, 200Hz, 160Hz, 100Hz, 80Hz, 60Hz, and 40Hz.

[0026] Specifically, the excitation methods of the laser vibration measurement module 202 include a hammer and a vibrator. The hammer is used to provide pulse excitation, which is suitable for transient excitation testing and generates broadband excitation by striking the object under test. The vibrator is used to provide steady-state or sinusoidal excitation at a specific frequency, which can precisely control the frequency and amplitude of the excitation and is suitable for test scenarios that require specific excitation conditions.

[0027] Specifically, the sensor module 203 uses two excitation methods, a force hammer and a vibrator, to excite the structure under test, and selects the appropriate excitation method according to the actual test requirements.

[0028] Specifically, the sensor module 204 consists of a laser source, an optical transmitting and receiving system, and a signal processing circuit. The laser source emits a stable laser beam, which is collimated by the optical transmitting system and then irradiates the surface of the object being measured. When the object being measured vibrates, the frequency of the reflected light will shift due to the Doppler effect. The optical receiving system collects the reflected light and interferes with the reference light to generate an interference signal containing vibration velocity information. Specifically, in sensor module 204, a piezoelectric accelerometer is used to collect vibration signals from the object under test, which serve as trigger and reference signals for data recording by the laser vibrometer. Specifically, the data acquisition module 205 performs real-time acquisition and storage of multi-channel (piezoelectric, laser) digital signals, and preprocesses the acquired data. Specifically, in the data processing module 206, the preprocessed data is processed and converted into signals such as velocity, displacement, and vibration frequency. Specifically, in the data display module 207, the velocity, displacement, and vibration frequency obtained from modal analysis are visualized in the form of charts, curves, and three-dimensional models.

[0029] Example 3 like Figure 3 As shown in Figure 4, this is an example of a mode shape and related component mode shape test under real-world conditions: At the site of a certain type of aircraft, a total station was used to calibrate 20 test points on the wing, wing lugs, the mounted payload, and the connection points, establishing a northeast-southeast coordinate system. First, a 100Hz sinusoidal excitation was applied to the aircraft using a vibrator. A laser vibrometer measured the vibration velocity signals at each test point, while a piezoelectric accelerometer simultaneously acquired reference signals. After data acquisition, the mode shape parameters of the wing were obtained using the above method, showing a large vibration displacement in the middle of the wing. Then, a force hammer was used to apply pulse excitation to the wing lugs. Analysis revealed a vibration displacement of 30µm at the connection point between the lug and the mounted payload, while the payload's vibration displacement was 100µm. The mode shape indicated the presence of a torsional vibration mode at the connection point.

[0030] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0031] In summary, this invention discloses a Doppler laser mode shape measurement method and apparatus, including a hardware system, a software system, and a calibration module. The mode shape testing system and method based on Doppler laser provided by this invention achieves high-precision, non-contact mode shape testing. The laser vibration measurement module utilizes the Doppler effect for non-contact measurement, avoiding the influence of contact measurement on the vibration characteristics of the measured object. The excitation module provides multiple excitation methods to adapt to different testing needs. The modal analysis module of the software system accurately extracts mode shape parameters using multiple algorithms. The calibration module ensures the measurement accuracy of the laser vibration meter. This process and method can be widely applied in mechanical engineering, aerospace, and other fields, providing a reliable basis for structural vibration analysis and optimization design.

Claims

1. A method for measuring Doppler laser mode shapes, characterized in that, include: S1, calibrate the laser vibration meter; S2, using a laser vibrometer to emit a laser, so that the emitted laser beam is precisely focused and perpendicularly illuminated on the test point on the surface of the object being measured; S3, acquire the time-domain vibration displacement signal; S4 preprocesses the time-domain vibration displacement signal, synchronizes the force signal, and obtains the effective time-domain vibration displacement signal. S5 processes the preprocessed effective time-domain vibration displacement signal to obtain vibration velocity, vibration displacement, and vibration frequency. S6 visualizes the vibration velocity, vibration displacement, and vibration frequency obtained from modal analysis.

2. The method according to claim 1, characterized in that, S1 includes: Place the standard vibration table in a stable laboratory environment and set the vibration frequency of the standard vibration table to different preset frequency values. Adjust the position of the single-point Doppler laser vibrometer so that its laser beam is perpendicularly irradiated onto the vibrating surface of the standard vibration table; Start the standard vibration table and laser vibrometer, collect acceleration, velocity and displacement data of the standard vibration table at different frequencies, compare and analyze the measurement results of the laser vibrometer with the theoretical values ​​of the standard vibration table, and calibrate if there is a deviation until the measurement results match.

3. The method according to claim 1, characterized in that, S2 include: Use a laser vibrometer mounted on the vibrator support frame to emit a laser beam. Adjust the distance between the laser vibrometer and the test point to be greater than or equal to 1 meter. Align the laser emission lens vertically with the test point so that the emitted laser beam is precisely focused and vertically illuminates the test point on the surface of the object being tested.

4. The method according to claim 1, characterized in that, S3 include: The laser vibrometer receives the laser signal reflected from the measured point, carrying the vibration information of the measured point. Through its internal photodetector and signal processing circuit, it acquires the raw waveform data of the displacement of the measured point along the laser beam direction over time. The sampling frequency is... Output the time-domain vibration displacement signal at the highest frequency of interest. .

5. The method according to claim 1, characterized in that, S4 include: S41: Synchronous acquisition of time-domain vibration displacement signal With input force signal Hardware-triggered synchronization is used to ensure time alignment. S42: Windowing process, applying a Hanning window to the time-domain signal to reduce spectral leakage. , where the window function T is the sampling duration; S43, Overlapping Segmentation, divides the signal into K segments, with each segment having a repetition rate of ≥50%, improving estimation stability.

6. The method according to claim 1, characterized in that, S5 include: S51: The vibration displacement signal is obtained by performing bandpass drift compensation integration on the effective time-domain vibration displacement signal. The calculation method is as follows: ; The S52 Fast Fourier Transform (FFT) performs an FFT on each segment of the time-domain signal. , Where k = 1, 2, 3, ... K, Angular frequency; S53 Input Power Spectrum and input-output cross power spectrum Obtain , ; S54: Frequency Response Function (FRF) acquisition, via... Calculate the frequency response function ; S55: Identification of mode shape parameters, using peak extraction method to analyze the FRF amplitude spectrum. Local maxima detection is performed to obtain the vibration frequency. , Where M is the modal order.

7. A Doppler laser mode shape measurement device, characterized in that, It includes a calibration module 201, a laser vibration measurement module 202, an excitation module 203, a sensor module 204, a data acquisition module 205, a data processing module 206, and a data display module 207, wherein: The calibration module 201 is connected to the laser vibration measurement module 202; the laser vibration measurement module 202, the excitation module 203, and the sensor module 204 are all connected to the input terminal of the data acquisition module 205, and the output terminal of the data acquisition module 205 is connected to the data processing module 206 and the data display module 207 in sequence.

8. The apparatus according to claim 7, characterized in that, Calibration module 201 is used to calibrate the measurement accuracy of the laser vibrometer; Laser vibration measurement module 202 is used to emit measurement lasers; Excitation module 203 is used to generate vibration signals; Sensor module 204 is used to collect vibration signals and trigger the data acquisition module to record data; Data acquisition module 205 is used to record vibration signals; The data processing module 206 is used to preprocess the collected vibration signals and convert them into mode physical quantities such as velocity, displacement, and vibration frequency. The data display module 207 is used to visualize and output the data processed by the data processing module.

9. The apparatus according to claim 7, characterized in that, The calibration frequency of calibration module 201 includes 256Hz, 200Hz, 160Hz, 100Hz, 80Hz, 60Hz, and 40Hz; the excitation methods of laser vibration measurement module 202 include hammer and vibrator; in sensor module 203, both hammer and vibrator are used to excite the structure under test, and the appropriate excitation method is selected according to the actual test requirements. The sensor module 204 includes a laser source, an optical transmitting and receiving system, and a signal processing circuit. The laser source emits a stable laser beam, which is collimated by the optical transmitting system and then irradiates the surface of the object being measured. When the object being measured vibrates, the frequency of the reflected light will shift due to the Doppler effect. The optical receiving system collects the reflected light and interferes with the reference light to generate an interference signal containing vibration velocity information.

10. The apparatus according to claim 7, characterized in that, In the data acquisition module 205, multi-channel digital signals are acquired and stored in real time, and the acquired data is preprocessed. The data processing module 206 processes the preprocessed data and converts it into velocity, displacement, and vibration frequency signals. The data display module 207 visualizes the velocity, displacement, and vibration frequency obtained from modal analysis in the form of charts, curves, and three-dimensional models.

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