A three-dimensional full-wavefield measurement method based on single-point laser Doppler vibrometer

Abstract

This invention discloses a three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer. By installing the single-point laser vibrometer at the end of a multi-degree-of-freedom robotic arm and combining it with a preset scanning path control program, it achieves multi-angle, automated scanning of the surface of a structure. Under signal excitation, the measurement system acquires vibration response signals from different incident directions and, combined with a spatial vector projection reconstruction algorithm, reconstructs the complete vibration components of the structure in three-dimensional space. Compared with traditional measurement solutions that require the use of three laser beams and precise alignment, this invention significantly simplifies the system hardware structure, reduces the complexity and operational difficulty of the measurement system, and improves the flexibility, accuracy, and adaptability of three-dimensional wavefield measurement.

Description

Technical Field

[0001] The invention belongs to the field of measurement technology, and in particular relates to a three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer. Background Art

[0002] Laser vibrometry technology, due to its non-contact nature, high sensitivity, and excellent spatial resolution, has been widely used in fields such as structural vibration analysis, acoustic imaging, and wave propagation research. In particular, the Laser Doppler Vibrometer (LDV), a non-contact vibration measurement instrument based on the Doppler effect, can accurately acquire velocity or displacement information of a target surface under minute vibration conditions. Compared to traditional accelerometers or contact sensors, laser vibrometry not only avoids sensor interference with the structure's inherent vibration characteristics but also offers a higher frequency response range and spatial resolution. Traditional three-dimensional laser vibrometry methods typically rely on multi-beam laser alignment systems. At each measurement point, three laser beams must be simultaneously focused from different directions on the target location to obtain the three orthogonal components at that point. These methods not only place extremely high demands on the laser beam's angle and positioning accuracy, but also place significant demands on the stability of the scanning control system and the complexity of the mechanical structure, severely limiting their experimental efficiency and engineering applicability. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, the present invention provides a three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer. By mounting the single-point laser vibrometer at the end of a multi-degree-of-freedom robotic arm and integrating it with a pre-set scanning path control program, this method enables multi-angle, automated scanning of a structure's surface. Under signal excitation, the measurement system acquires vibration response signals from different incident directions and, combined with a spatial vector projection reconstruction algorithm, reconstructs the complete vibration components of the structure in three dimensions. Compared to traditional measurement schemes that require the precise alignment of three laser beams, this method significantly simplifies the system hardware structure, reduces the complexity and operational difficulty of the measurement system, and enhances the flexibility, accuracy, and adaptability of three-dimensional wavefield measurement.

[0004] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0005] Step 1: Fix the structure under test on a vibration-damping table to ensure that no additional vibration interference is generated during the measurement process. Install a single-point laser Doppler vibrometer (LDV) on the end of the robotic arm and adjust the LDV position and incident angle to obtain the reflected signal.

[0006] Step 2: Define the measurement area on the surface of the structure to be measured and set the point distribution density to meet the spatial resolution requirements; set the sampling frequency and time length based on the frequency range of the excitation signal and the dynamic characteristics of the structure to ensure the integrity and accuracy of the data;

[0007] Step 3: The integrated software controls the signal generator to output a preset excitation signal, which then passes through a power amplifier to the vibrator or piezoelectric element, stimulating the structure to produce a vibration response. Simultaneously, the embedded control system uses the LDV to measure the velocity of a single point aligned with the laser beam. The robotic arm then moves the LDV along a preset path, sequentially scanning each point within the measurement area and collecting the vibration time-domain signal at each measurement point.

[0008] Step 4: By controlling the joint angle of the robotic arm and changing the incident direction of the LDV, multi-angle measurement of the same measuring point is achieved, and velocity data at three different incident angles is measured. At each new incident angle, the process of step 3 is repeated to obtain vibration projection data at different incident angles.

[0009] Step 5: Integrate the vibration projection data at each incident angle and, combined with known geometric relationships, construct a three-dimensional vibration vector of the measuring point. Utilize the spatial vector projection reconstruction algorithm to separate and reconstruct the vibration components of the target area in three-dimensional space.

[0010] Step 6: Post-process the separated signals to reconstruct the wave fields at different incident angles. Through data fusion and visualization, extract the corresponding time-domain wave field evolution process and frequency-domain response characteristics.

[0011] Furthermore, in step 3, the LDV measures the velocity of a single point in the direction aligned with the laser beam, and the velocity component of the single point is expressed as:

[0012]

[0013] in represents three different incident angles, 、 、 represents the velocity components along the orthogonal axes in a rectangular coordinate system, 、 、 Represent the laser unit vectors The angles with the x, y, and z axes.

[0014] Furthermore, in step 4, the vector relationship of the velocity data at three different incident angles in three directions is written into a matrix form:

[0015]

[0016] in, 、 、 Represent the velocities measured at three different incident angles, and the orthogonal components of the velocities are expressed as:

[0017] .

[0018] Furthermore, the vibration component of the target area in three-dimensional space is constructed by the following formula:

[0019]

[0020] in, Indicates time, and Indicates the position coordinates of the measurement point, 、 、 They represent the time domain signals of the velocity components along the orthogonal axes in the rectangular coordinate system, 、 、 Represents the velocity time domain signals measured at three different incident angles.

[0021] Furthermore, the adjustment of the LDV position and the incident angle is achieved by adjusting the joint angle of the laser vibrometer through integrated software.

[0022] Furthermore, in step 2, defining the measurement area, setting the point distribution density, sampling frequency, and sampling time are performed through integrated software.

[0023] Furthermore, step 6 is performed using computer software Wolfram Mathematica.

[0024] Furthermore, the device for implementing the three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer includes a single-point laser Doppler vibrometer, a six-axis robotic arm, a signal generator, a signal amplifier, an exciter, an oscilloscope, a central control computer, and an integrated software for controlling the above-mentioned device.

[0025] Furthermore, the preset path in step 3 is of any shape.

[0026] Furthermore, the structure to be measured is a structure of arbitrary shape.

[0027] Furthermore, the structure to be measured is in the shape of a flat plate or a circular shell.

[0028] The beneficial effects of the present invention are as follows:

[0029] The present invention breaks through the technical limitations of traditional three-dimensional vibration measurement, which relies on multiple vibrometers and complex alignment systems. Compared with the existing technology, the present invention only requires a single-point laser Doppler vibrometer, and automatically controls the scanning path and laser incident angle through a robotic arm, thereby realizing the multi-directional vibration information collection of the measurement area and accurately reconstructing the three-dimensional wave field components based on the spatial projection relationship. This method significantly reduces the number of equipment and system complexity, avoids the tedious operation of precisely aligning multiple laser beams at each measuring point, and improves the flexibility and automation level of the measurement. The proposed method has high measurement accuracy and a wide range of applications. It is particularly suitable for three-dimensional vibration and wave field testing of complex structural parts and space-constrained environments, and has significant engineering application value and promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is an exemplary flow chart of the method of the present invention;

[0031] Figure 2 Schematic diagram of the measurement process of the method of the present invention;

[0032] Figure 3 This is a diagram of the aluminum plate being tested in an embodiment of the present invention;

[0033] Figure 4 This is a single-point time domain signal diagram according to an embodiment of the present invention;

[0034] FIG5( a ) is a time domain signal diagram of A0 separation according to an embodiment of the present invention;

[0035] FIG5( b ) is a time domain signal diagram of S0 separation according to an embodiment of the present invention;

[0036] Figure 6 This is a frequency domain wave field numerical simulation diagram of an embodiment of the present invention;

[0037] Figure 7 Graph showing the frequency domain wave field experimental results of an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings and examples.

[0039] like Figure 1 and Figure 2 As shown, the present invention proposes a three-dimensional wave field measurement method based on a single-point laser Doppler vibrometer to achieve automated measurement of the three-dimensional vibration of a target structure, including the following steps:

[0040] Step 1: Secure the structure to be measured firmly on a vibration-damping table to ensure that no additional vibration interference is generated during the measurement. Mount a single-point laser Doppler vibrometer (LDV) on the end of the robotic arm and adjust the LDV position and incident angle to obtain a stable and strong reflected signal.

[0041] Step 2: Define the measurement area on the surface of the structure to be measured and set an appropriate point distribution density to meet the spatial resolution requirements; set an appropriate sampling frequency and time length based on the frequency range of the excitation signal and the dynamic characteristics of the structure to ensure data integrity and accuracy;

[0042] Step 3: The integrated software controls the signal generator to output a preset excitation signal, which then passes through a power amplifier to the vibrator or piezoelectric plate, stimulating the structure to produce a vibration response. Simultaneously, the embedded control system uses the LDV to measure the velocity of a single point aligned with the laser beam. The robotic arm then moves the LDV along a preset path, sequentially scanning each point within the measurement area and collecting the vibration time-domain signal at each measurement point. The processed data is then saved for subsequent analysis.

[0043] Step 4: By controlling the joint angle of the robotic arm and changing the incident direction of the LDV, multi-angle measurement of the same measuring point is achieved, and velocity data at three different incident angles is measured. At each new incident angle, the process of step 3 is repeated to obtain vibration projection data in different directions.

[0044] Step 5: Integrate the vibration projection data at each incident angle and, combined with known geometric relationships, construct a three-dimensional vibration vector of the measuring point. Utilize the spatial vector projection reconstruction algorithm to separate and reconstruct the vibration components of the target area in three-dimensional space.

[0045] Step 6: Post-process the separated signals and reconstruct the wave fields in each direction. Through data fusion and visualization processing, extract the corresponding time domain wave field evolution process and frequency domain response characteristics.

[0046] In step 3, the LDV measures the velocity of a single point in the direction aligned with the laser beam. The velocity component of the single point is expressed as:

[0047]

[0048] In step 4, the vector relationship of the velocity data in three directions at three different incident angles is written in matrix form:

[0049]

[0050] The orthogonal components of velocity are expressed as:

[0051]

[0052] The vibration components of the target area in three-dimensional space are constructed by the following formula:

[0053]

[0054] Adjusting the LDV position and incident angle is achieved by adjusting the laser vibrometer joint angle through the integrated software.

[0055] In step 2, the measurement area is defined, and the point distribution density, sampling frequency, and sampling time are set through the integrated software.

[0056] In step 6, the computer software Wolfram Mathematica is used to reconstruct the wave fields in various directions, perform data fusion and visualization.

[0057] The implementation device of the present invention includes a single-point laser Doppler vibrometer, a six-axis robotic arm, a signal generator, a signal amplifier, an exciter, an oscilloscope, a central control computer, and an integrated software for controlling the above-mentioned devices.

[0058] The preset path in step 3 is an arbitrary shape.

[0059] The structure to be measured is a flat plate, a circular shell or a structure of any shape.

[0060] Example:

[0061] This example demonstrates a 3D full-wavefield measurement method based on a single-point vibrometer. The device includes a single-point laser Doppler vibrometer (LDV), a six-axis robotic arm, a signal generator, a signal amplifier, an exciter, an oscilloscope, a central control computer, and integrated software for controlling the above-mentioned devices. The specific steps are as follows:

[0062] (1) Place the aluminum plate specimen to be tested horizontally and lay sound insulation cotton around it to prevent the plate from contacting the vibration damping platform. At the same time, evenly wrap the edge of the aluminum plate with blue tack to further weaken the reflection interference of the structure boundary, thereby creating an experimental condition close to a free infinite boundary. Figure 3 As shown in the figure, in order to excite in-plane (S0 mode) and out-of-plane (A0 mode) fluctuations, several ceramic piezoelectric sheets (PZT) are pasted at symmetrical positions on the front and back of the aluminum plate.

[0063] (2) If Figure 3 As shown, a single-point LDV is mounted on the end effector of a six-axis robotic arm. The arm's joint angles and extension position are adjusted so that the LDV laser beam strikes the aluminum plate surface at a preset angle of incidence, α. Under integrated software control, the echo signal intensity is monitored in real time. Fine-tuning the angle of incidence and the position of the vibrometer ensures a strong, stable echo signal with a high signal-to-noise ratio, ensuring subsequent high-quality data acquisition.

[0064] (3) The automatic measurement process is started by the central control software. On the one hand, the control signal generator outputs an excitation signal with a center frequency of 60kHz. After the signal is amplified by the power amplifier, it drives the ceramic piezoelectric piece to stimulate the structural vibration response. On the other hand, the robotic arm drives the LDV to move point by point along the measurement area according to the preset scanning path, and stays steadily at each preset measurement point to collect the time domain vibration velocity signal of the point. The collected time domain signal is as follows: Figure 4 All collected signals are transmitted and stored in real time, completing the first full-area scan (in the α incident direction).

[0065] (4) The software runs automatically. On the one hand, the control signal generator excites a signal with a center frequency of 60 kHz. The signal is modulated by the power amplifier and then generates a vibration response through the ceramic piezoelectric plate. Then, the robotic arm moves the LDV along the preset path, scanning each point in the measurement area in turn, and collecting the vibration time domain signal at each measurement point. The robotic arm moves the LDV along the preset path, scanning each point in the measurement area in turn, and collecting the vibration time domain signal at each measurement point.

[0066] (5) After completing the first scan, the robot arm is manipulated to adjust the angles of each joint so that the LDV laser beam is directed toward the aluminum plate surface along the new incident direction (angle β and angle γ), maintaining the same distribution of measurement points as in the first scan. Repeat step (4) to collect vibration signals from each measurement point at different incident angles to ensure that complete vibration information is obtained in multiple directions, providing basic data support for subsequent three-dimensional component reconstruction.

[0067] (6) Based on the vibration signals obtained at different incident angles, the spatial vector projection reconstruction algorithm is used, combined with the geometric relationship between the laser beam incident angle and the surface normal vector, to separate and accurately calculate the vibration vector components of each measuring point in the three-dimensional coordinate system. Examples of separated time domain signals are shown in Figures 5 (a) and 5 (b). Through this algorithm, the in-plane S0 modal wave field and the out-of-plane A0 modal wave field can be extracted respectively. Subsequently, the Wolfram Mathematica platform is used to perform fast Fourier transform (FFT) processing on the time domain vibration data to obtain the amplitude and phase distribution of each frequency component. Combining data interpolation and image processing technology, dynamic images of the wave field evolving over time in the time domain and wave field amplitude distribution diagrams at each frequency in the frequency domain are constructed respectively, realizing a full range of visualization of the three-dimensional wave field. The frequency domain results of the numerical simulation A0 wave and S0 wave field at 60 kHz are shown in Figure 5. Figure 6 As shown in the figure, the frequency domain results of the A0 and S0 wave fields obtained at 60 kHz are as follows: Figure 7 As shown, the two are basically consistent.

Claims

1. A three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer, characterized in that: The steps include: Step 1: Fix the structure under test on a vibration-damping table to ensure that no additional vibration interference is generated during the measurement process. Install a single-point laser Doppler vibrometer (LDV) on the end of the robotic arm and adjust the LDV position and incident angle to obtain the reflected signal. Step 2: Define the measurement area on the surface of the structure to be measured and set the point distribution density to meet the spatial resolution requirements; set the sampling frequency and time length based on the frequency range of the excitation signal and the dynamic characteristics of the structure to ensure the integrity and accuracy of the data; Step 3: The integrated software controls the signal generator to output a preset excitation signal, which then passes through a power amplifier to the vibrator or piezoelectric element, stimulating the structure to produce a vibration response. Simultaneously, the embedded control system uses the LDV to measure the velocity of a single point aligned with the laser beam. The robotic arm then moves the LDV along a preset path, sequentially scanning each point within the measurement area and collecting the vibration time-domain signal at each measurement point. The velocity component of the single point is expressed as: in i =v·e i =in x cosα i +in y cosβ i +in z cosγ i ; Where i=1, 2, 3 represents three different incident angles, v x 、v y 、v z represents the velocity component along the orthogonal axis in the rectangular coordinate system, α i , β i , γ i Denote the laser unit vector e i The angles with the x, y, and z axes; Step 4: By controlling the joint angle of the robotic arm and changing the incident direction of the LDV, multi-angle measurement of the same measuring point is achieved, and velocity data at three different incident angles is measured. At each new incident angle, the process of step 3 is repeated to obtain vibration projection data at different incident angles. The vector relationship of the velocity data at the three different incident angles in three directions is written in matrix form: Among them, v1, v2, and v3 represent the velocities measured at three different incident angles, and the orthogonal components of the velocities are expressed as: Step 5: Integrate the vibration projection data at each incident angle and, combined with known geometric relationships, construct a three-dimensional vibration vector of the measuring point. Utilize the spatial vector projection reconstruction algorithm to separate and reconstruct the vibration components of the target area in three-dimensional space. The vibration components of the target area in three-dimensional space are constructed by the following formula: Where t represents time, x and y represent the position coordinates of the measurement point, and v x (x,y,t),v y (x,y,t),v z (x, y, t) represents the time domain signal of the velocity component along the orthogonal axis in the rectangular coordinate system, v1(x, y, t), v2(x, y, t), and v3(x, y, t) represent the velocity time domain signals measured at three different incident angles; Step 6: Post-process the separated signals to reconstruct the wave fields at different incident angles. Through data fusion and visualization, extract the corresponding time-domain wave field evolution process and frequency-domain response characteristics.

2. The three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer according to claim 1, characterized in that: The adjustment of the LDV position and the incident angle is achieved by adjusting the joint angle of the laser vibrometer through integrated software.

3. The three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer according to claim 2, characterized in that: In step 2, defining the measurement area, setting the point distribution density, sampling frequency, and sampling time are performed through integrated software.

4. The three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer according to claim 3, characterized in that: The step 6 is performed using computer software Wolfram Mathematica.

5. The three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer according to claim 4, characterized in that: The device for implementing the three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer includes a single-point laser Doppler vibrometer, a six-axis robotic arm, a signal generator, a signal amplifier, an exciter, an oscilloscope, a central control computer, and integrated software for controlling the above-mentioned devices.

6. The three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer according to claim 5, characterized in that: The preset path in step 3 is of any shape.

7. The three-dimensional full-wavefield measurement method based on a single-point laser Doppler vibrometer according to claim 6, characterized in that: The structure to be measured is a structure of any shape.

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