CN115452125B - Structural vibration video measurement method and system based on space time direction division method - Google Patents
Structural vibration video measurement method and system based on space time direction division method Download PDFInfo
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Abstract
The invention provides a structure vibration video measurement method and system based on a space time direction subtraction method. The technical field of structural vibration video measurement comprises the steps of acquiring a time sequence change image sequence of structural vibration by using a camera; processing the time sequence change image sequence by using a space-frequency conversion method to obtain a first frequency domain space complex characteristic sequence; processing adjacent frames of the first frequency domain space complex feature sequence by utilizing space time division to obtain a second frequency domain space complex feature sequence; operating a second frequency domain space complex characteristic sequence by using four-quadrant arctangent operation to acquire phase change of adjacent frames rich in relative displacement change field information; calculating a conversion scale factor of the measured object; calculating the actual amplitude of the structural vibration in time sequence; and calculating the frequency of the vibration of the tested structure. The invention does not need preprocessing operation, avoids complex and time-consuming unwrapping operation in the space-frequency domain conversion process, and simultaneously removes background noise accurately, thereby having high robustness, strong noise resistance and high running speed.
Description
Technical Field
The invention belongs to the technical field of structural vibration video measurement, and particularly relates to a structural vibration video measurement method and system based on a space time direction removal method.
Background
Vibration test analysis has great significance in the fields of scientific research and engineering application. The traditional vibration test analysis mostly adopts a contact method, and has the defects of complicated wiring, difficult installation, low spatial resolution, loading effect and the like. Along with the technical development, non-contact methods such as a laser Doppler vibration measurement method, a video measurement method and the like are widely applied to the field of vibration measurement, and the defects are effectively overcome. However, the laser Doppler vibration meter has the problems of low measurement speed, huge structure, high price and the like. The vibration measurement method based on the video gradually becomes an important component in the technical field of vibration measurement due to the advantages of non-contact, high precision, high spatial resolution, full-view field measurement, convenient operation, simple structure and the like.
In order to cope with the drawbacks caused by the traditional vibration measurement, the application of Digital Image Correlation (DIC) technology in the vibration measurement field is widely developed, and the motion measurement based on digital video has the advantages of low cost, high portability, global measurement and the like, thereby providing a brand new view angle for the motion measurement technology. The existing video measurement technology also comprises an optical flow method, and the method combines image detection methods such as image pixel values, edge detection and the like to realize vibration response measurement of the video method. The patent with publication number CN106989812 proposes a mode measurement method of a large fan blade based on a photogrammetry technology, a double camera is required to be adopted in the acquisition process, and the mode of the blade is analyzed through a stereoscopic matching technology of DIC. Although the DIC technique can obtain high-precision data, it requires an ultra-high amount of computation as a whole, and it is impossible to monitor and process data in real time under the prior art. Meanwhile, the features such as speckle and the like are required to be precoated on the measured object. The patent with publication number CN114187330 proposes a structure micro-amplitude vibration working mode analysis method based on an optical flow method, which takes a structure contour point obtained by the optical flow method as a main characteristic, and reflects real change by displacement change of the contour point. However, the methods have high requirements on acquisition conditions, need to strictly ensure that no other motion interference exists in the scene of the vibration area, have large calculated amount and low calculated speed, and have certain requirements on the acquisition frame rate of the camera.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a structure vibration video measurement method and system based on space time alignment method.
The invention is realized by the following technical scheme, and provides a structural vibration video measurement method based on space time direction removal, which specifically comprises the following steps:
step 1, performing video acquisition on a vibration process of a detected structure by using a camera at a frame rate meeting a Nyquist sampling rate to obtain a time sequence change image sequence rich in vibration information;
Step 2, converting the acquired time sequence change image sequence into a frequency domain frame by using a space-frequency conversion method, and obtaining a first frequency domain space complex characteristic sequence rich in phase characteristics and amplitude characteristics of motion profile vibration information;
step 3, directly processing adjacent frames of the first frequency domain space complex feature sequence in the frequency domain by utilizing space time division to obtain a second frequency domain space complex feature sequence rich in phase change of the adjacent frames;
Step 4, operating the second frequency domain space complex characteristic sequence by utilizing four-quadrant arctangent operation to acquire the phase change of the adjacent frames rich in the relative displacement change field information;
Step 5, calculating a conversion scale factor of the actual displacement of the measured object in the actual space plane motion and the motion size of the object in the camera plane under the actual measurement distance;
Step 6, calculating the actual amplitude of the structural vibration on the time sequence by using the time sequence relative displacement change field and the conversion scale factor;
And 7, obtaining the vibration frequency of the structure to be tested through fast Fourier transform according to the time sequence actual displacement field.
Further, the space-frequency conversion method comprises Gabor wave conversion, hilbert conversion and log-Gabor conversion.
Further, the image space feature conversion process of the Gabor wave specifically includes:
(1) Converting the acquired image into a gray characteristic image, and selecting a wavelength and a direction suitable for Gabor according to vibration information of a structure to be detected;
(2) Convolving the Gabor wave with the gray characteristic image in a space domain to obtain a first frequency domain space complex characteristic sequence of the image in a frequency domain, and defining space complex characteristics of adjacent frames as I g (u, v, t) and I g (u, v, t+Δt) respectively, wherein t represents the current moment, Δt represents a time step, and (u, v) is a frequency domain coordinate;
(3) Solving the amplitude of the complex features of the image by using abs (·) operators to obtain the amplitude features of each pixel position:
Where 2 represents the absolute value.
Further, the step 3 specifically includes:
(1) Dynamically selecting the frequency domain space complex characteristics of two frames of images with adjacent time sequences
Wherein A (u, v, t) and A (u, v, t+Δt) respectively correspond to frequency domain magnitudes of different frames, f 0 is frequency, and Δy is relative displacement variation in the y direction;
(2) Processing the phase characteristics of the selected adjacent frame images by using a division operator, and deriving by complex integral operation to obtain second frequency domain space complex characteristics, namely
(3) And continuously repeating the time division step along the time sequence direction on the first frequency domain space complex characteristic sequence to obtain a second frequency domain space complex characteristic sequence.
Further, in the step 4, the calculation formula for operating the second frequency domain space complex feature sequence by using the four-quadrant arctangent operation specifically includes:
Thereby acquiring phase changes of adjacent frames rich in relative displacement change field information
Further, in the conversion process of the actual distance and the pixel distance in step5, the conversion factor of the camera coordinate system and the world coordinate system varies with the acquisition distance of the camera.
Further, in the step 7, in the process of calculating the frequency domain information by using the obtained actual displacement field, the time sequence actual displacement field needs to ensure at least one period of the time sequence actual displacement field.
The invention provides a structural vibration video measurement system based on a space time direction removal method, which specifically comprises the following steps:
And the acquisition module is used for: the method comprises the steps of utilizing a camera to acquire video of a vibration process of a detected structure at a frame rate meeting a Nyquist sampling rate, and acquiring a time sequence change image sequence rich in vibration information;
And a conversion module: converting the acquired time sequence change image sequence into a frequency domain frame by using a space-frequency conversion method, and obtaining a first frequency domain space complex characteristic sequence rich in phase characteristics and amplitude characteristics of motion profile vibration information;
A division module: directly processing adjacent frames of the first frequency domain space complex feature sequence in the frequency domain by utilizing space time division to obtain a second frequency domain space complex feature sequence rich in phase change of the adjacent frames;
arc tangent module: operating the second frequency domain space complex characteristic sequence by using four-quadrant arctangent operation to obtain the phase change of the adjacent frames rich in the relative displacement change field information;
A conversion scale factor calculation module: calculating a conversion scale factor of the actual displacement of the measured object in the actual space plane motion and the motion size of the object in the camera plane under the actual measurement distance;
The amplitude calculating module is used for: calculating the actual amplitude of the structural vibration on the time sequence by using the time sequence relative displacement change field and the conversion scale factor;
And a frequency calculation module: and obtaining the vibration frequency of the tested structure through fast Fourier transform according to the time sequence actual displacement field.
The beneficial effects of the invention are as follows:
1. Compared with the DIC method, the method disclosed by the invention has the advantages that pretreatment operations such as pre-coating speckle on the measured object are not needed, and a more convenient and simple measurement process is realized; high-precision data can be obtained under the condition of meeting the basic sampling rate, the hardware requirement is lower, and the cost is lower.
2. Compared with methods such as an optical flow method, the method provided by the invention utilizes space time division to directly extract the phase change of the adjacent frames rich in the relative displacement change field information in the frequency domain, effectively avoids the unwrapping operation used for phase extraction but complicated and time-consuming in the space-frequency domain conversion process, and simultaneously removes the background noise more accurately, so that the method provided by the invention has the advantages of higher overall robustness, better noise resistance and higher running speed.
Drawings
FIG. 1 is a schematic flow chart of space-time division.
Fig. 2 is a photograph of a cantilever in the actual camera plane.
Fig. 3 is a spatial time division actual time domain measurement.
Fig. 4 is a spatial time division actual frequency domain measurement.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1-4, the invention provides a structural vibration video measurement method based on space time direction subtraction, which specifically comprises the following steps:
step 1, performing video acquisition on a vibration process of a detected structure by using a camera at a frame rate meeting a Nyquist sampling rate to obtain a time sequence change image sequence rich in vibration information;
Step 2, converting the acquired time sequence change image sequence into a frequency domain frame by using a space-frequency conversion method, and obtaining a first frequency domain space complex characteristic sequence rich in phase characteristics and amplitude characteristics of motion profile vibration information;
step 3, directly processing adjacent frames of the first frequency domain space complex feature sequence in the frequency domain by utilizing space time division to obtain a second frequency domain space complex feature sequence rich in phase change of the adjacent frames;
Step 4, operating the second frequency domain space complex characteristic sequence by utilizing four-quadrant arctangent operation to acquire the phase change of the adjacent frames rich in the relative displacement change field information;
Step 5, calculating conversion scale factors of actual displacement of the measured object in the actual space plane motion and the motion size (pixel) of the object in the camera plane under the actual measurement distance;
Step 6, calculating the actual amplitude of the structural vibration on the time sequence by using the time sequence relative displacement change field and the conversion scale factor;
And 7, obtaining the vibration frequency of the structure to be tested through fast Fourier transform according to the time sequence actual displacement field.
The space-frequency conversion method described in step 2 includes, but is not limited to, gabor wave conversion, hilbert conversion, and log-Gabor conversion.
Taking the image space feature conversion process of the Gabor wave as an example, the image space feature conversion process of the Gabor wave specifically includes:
(1) Converting the acquired image into a gray characteristic image, and selecting a wavelength and a direction suitable for Gabor according to vibration information of a structure to be detected;
(2) Convolving the Gabor wave with the gray characteristic image in a space domain to obtain a first frequency domain space complex characteristic sequence of the image in a frequency domain, and defining space complex characteristics of adjacent frames as I g (u, v, t) and I g (u, v, t+Δt) respectively, wherein t represents the current moment, Δt represents a time step, and (u, v) is a frequency domain coordinate;
(3) Solving the amplitude of the complex features of the image by using abs (·) operators to obtain the amplitude features of each pixel position:
Where 2 represents the absolute value.
The step 3 specifically comprises the following steps:
(1) Dynamically selecting the frequency domain space complex characteristics of two frames of images with adjacent time sequences
Wherein A (u, v, t) and A (u, v, t+Δt) respectively correspond to frequency domain magnitudes of different frames, f 0 is frequency, and Δy is relative displacement variation in the y direction;
(2) Processing the phase characteristics of the selected adjacent frame images by using a division operator, and deriving by complex integral operation to obtain second frequency domain space complex characteristics, namely
(3) And continuously repeating the time division step along the time sequence direction on the first frequency domain space complex characteristic sequence to obtain a second frequency domain space complex characteristic sequence.
In the step 4, the calculation formula for operating the second frequency domain space complex feature sequence by using the four-quadrant arctangent operation specifically includes:
Thereby acquiring phase changes of adjacent frames rich in relative displacement change field information
In the step 5, in the conversion process of the actual distance and the pixel distance, the conversion factors of the camera coordinate system and the world coordinate system change along with the acquisition distance of the camera.
In the step 7, in the process of calculating the frequency domain information by using the obtained actual displacement field, the actual displacement field with time sequence needs to ensure at least one period of the actual displacement field with time sequence.
The invention provides a structural vibration video measurement system based on a space time direction removal method, which specifically comprises the following steps:
And the acquisition module is used for: the method comprises the steps of utilizing a camera to acquire video of a vibration process of a detected structure at a frame rate meeting a Nyquist sampling rate, and acquiring a time sequence change image sequence rich in vibration information;
And a conversion module: converting the acquired time sequence change image sequence into a frequency domain frame by using a space-frequency conversion method, and obtaining a first frequency domain space complex characteristic sequence rich in phase characteristics and amplitude characteristics of motion profile vibration information;
A division module: directly processing adjacent frames of the first frequency domain space complex feature sequence in the frequency domain by utilizing space time division to obtain a second frequency domain space complex feature sequence rich in phase change of the adjacent frames;
arc tangent module: operating the second frequency domain space complex characteristic sequence by using four-quadrant arctangent operation to obtain the phase change of the adjacent frames rich in the relative displacement change field information;
A conversion scale factor calculation module: calculating a conversion scale factor of the actual displacement of the measured object in the actual space plane motion and the motion size of the object in the camera plane under the actual measurement distance;
The amplitude calculating module is used for: calculating the actual amplitude of the structural vibration on the time sequence by using the time sequence relative displacement change field and the conversion scale factor;
And a frequency calculation module: and obtaining the vibration frequency of the tested structure through fast Fourier transform according to the time sequence actual displacement field.
For a better description of the method according to the application, the following examples are presented to illustrate a complete flow of the method for measuring vibrations of a rapid full-field structure based on space-time division according to the application in practical use.
In this embodiment, a method for measuring a rapid full-field structure vibration based on space time division is specifically provided, and the flow chart of the steps is shown in fig. 1, specifically including the following steps:
(1) A cantilever beam with the length of 20cm is prepared, and as shown in fig. 2, a force hammer is used for exciting the bottom of the cantilever beam to excite a vibration mode.
(2) The vibration process of the cantilever of the measured object is acquired and recorded by utilizing shooting equipment such as a smart phone, a common camera or a high-speed industrial camera, so that a video containing cantilever vibration information is obtained, and meanwhile, vibration data is measured by using a traditional contact method (an accelerometer measurement method) to be used as a comparison reference value. In the acquisition process, the acquisition frame rate is set to 180Hz, and the LED light source is utilized for light filling.
(3) The wavelength of Gabor wave is set to 4, which is generally common, and the setting direction is 0 ° in the vibration direction. And processing the acquired images frame by using the set Gabor waves to realize the feature conversion from a space domain to a frequency domain to obtain the I g (u, v, t) and the I g (u, v, t+Δt), wherein t represents the current moment, Δt represents the time step, and (u, v) is the frequency domain coordinate. The method can also be obtained by directly adopting Hilbert transform without setting prior conditions.
(4) Obtaining the amplitude of the complex image features by using abs (·) operators, wherein the image features in the frequency domain are complex values, and obtaining the amplitude features of each pixel point position:
Where 2 represents the absolute value.
(5) Processing the first frequency domain space complex characteristics between every two adjacent frames of each time sequence by adopting time division instead of directly solving a phase difference value, and utilizing a formula:
Wherein A (u, v, t) and A (u, v, t+Δt) correspond to the frequency domain magnitudes of different frames, respectively, and f 0 is the frequency.
According to complex operation characteristics, processing first space frequency domain complex characteristics between every two adjacent frames on time sequence by utilizing a division operator, and utilizing a formula:
obtaining a second spatial frequency domain complex characteristic comprising a phase difference. The above process is repeated for each pair of adjacent frames in time series.
(6) Processing the obtained second space frequency domain complex characteristic containing the phase difference by adopting a four-quadrant arctan operator arctan (DEG), and utilizing a formulaAnd obtaining a phase change field in the video, namely a real-time relative motion displacement field.
(7) And calculating the conversion scale factor of the actual displacement of the measured object moving in the actual space plane and the moving size (pixel) of the object in the camera plane under the actual measuring distance to be 5.2mm/pixel.
(8) The time sequence relative motion displacement field is multiplied by the conversion scale factor to obtain an actual motion field, a time domain measurement result is shown in fig. 3, and a frequency domain field of the vibration displacement signal is obtained through Fourier transformation, and a result is shown in fig. 4.
(9) And comparing the coincidence degree of the actual measurement data and the data of the invention, wherein the calculation result is 99.1%.
The above describes in detail a method and a system for measuring structural vibration video based on space time-oriented method, and specific examples are applied to illustrate the principle and implementation of the present invention, and the above description of the examples is only used to help understand the method and core idea of the present invention; meanwhile, as those skilled in the art will have variations in the specific embodiments and application scope in accordance with the ideas of the present invention, the present description should not be construed as limiting the present invention in view of the above.
Claims (5)
1. The structural vibration video measurement method based on the space time direction method is characterized by comprising the following steps of:
step 1, performing video acquisition on a vibration process of a detected structure by using a camera at a frame rate meeting a Nyquist sampling rate to obtain a time sequence change image sequence rich in vibration information;
Step 2, converting the acquired time sequence change image sequence into a frequency domain frame by using a space-frequency conversion method, and obtaining a first frequency domain space complex characteristic sequence rich in phase characteristics and amplitude characteristics of motion profile vibration information;
step 3, directly processing adjacent frames of the first frequency domain space complex feature sequence in the frequency domain by utilizing space time division to obtain a second frequency domain space complex feature sequence rich in phase change of the adjacent frames;
Step 4, operating the second frequency domain space complex characteristic sequence by utilizing four-quadrant arctangent operation to acquire the phase change of the adjacent frames rich in the relative displacement change field information;
Step 5, calculating a conversion scale factor of the actual displacement of the measured object in the actual space plane motion and the motion size of the object in the camera plane under the actual measurement distance;
Step 6, calculating the actual amplitude of the structural vibration on the time sequence by using the time sequence relative displacement change field and the conversion scale factor;
Step 7, obtaining the vibration frequency of the structure to be tested through fast Fourier transform according to the time sequence actual displacement field;
the space-frequency conversion method comprises Gabor wave conversion, hilbert conversion and log-Gabor conversion;
The image space feature conversion process of the Gabor wave specifically includes:
(1) Converting the acquired image into a gray characteristic image, and selecting a wavelength and a direction suitable for Gabor according to vibration information of a structure to be detected;
(2) Convolving the Gabor wave with the gray characteristic image in a space domain to obtain a first frequency domain space complex characteristic sequence of the image in a frequency domain, and defining space complex characteristics of adjacent frames as I g (u, v, t) and I g (u, v, t+Δt) respectively, wherein t represents the current moment, Δt represents a time step, and (u, v) is a frequency domain coordinate;
(3) Solving the amplitude of the complex features of the image by using abs (·) operators to obtain the amplitude features of each pixel position:
wherein |· | 2 represents the absolute value;
the step 3 specifically comprises the following steps:
(1) Dynamically selecting the frequency domain space complex characteristics of two frames of images with adjacent time sequences
Wherein A (u, v, t) and A (u, v, t+Δt) respectively correspond to frequency domain magnitudes of different frames, f 0 is frequency, and Δy is relative displacement variation in the y direction;
(2) Processing the phase characteristics of the selected adjacent frame images by utilizing a division operator, deriving through complex integral operation to obtain second frequency domain space complex characteristics, namely
(3) And continuously repeating the time division step along the time sequence direction on the first frequency domain space complex characteristic sequence to obtain a second frequency domain space complex characteristic sequence.
2. The method of claim 1, wherein the calculation formula for operating the second frequency domain spatial complex signature sequence using the four-quadrant arctangent operation in step 4 is specifically:
Thereby acquiring phase changes of adjacent frames rich in relative displacement change field information
3. The method of claim 1, wherein the conversion factor of the camera coordinate system and the world coordinate system varies with the acquisition distance of the camera during the conversion of the actual distance to the pixel distance in step 5.
4. The method of claim 1, wherein in the calculating of the frequency domain information using the obtained actual displacement field in step 7, at least one period of the time-series actual displacement field is required to be ensured using the time-series actual displacement field.
5. The utility model provides a structure vibration video measurement system based on space time to method of removing which characterized in that, the system specifically includes:
And the acquisition module is used for: the method comprises the steps of utilizing a camera to acquire video of a vibration process of a detected structure at a frame rate meeting a Nyquist sampling rate, and acquiring a time sequence change image sequence rich in vibration information;
And a conversion module: converting the acquired time sequence change image sequence into a frequency domain frame by using a space-frequency conversion method, and obtaining a first frequency domain space complex characteristic sequence rich in phase characteristics and amplitude characteristics of motion profile vibration information;
A division module: directly processing adjacent frames of the first frequency domain space complex feature sequence in the frequency domain by utilizing space time division to obtain a second frequency domain space complex feature sequence rich in phase change of the adjacent frames;
arc tangent module: operating the second frequency domain space complex characteristic sequence by using four-quadrant arctangent operation to obtain the phase change of the adjacent frames rich in the relative displacement change field information;
A conversion scale factor calculation module: calculating a conversion scale factor of the actual displacement of the measured object in the actual space plane motion and the motion size of the object in the camera plane under the actual measurement distance;
The amplitude calculating module is used for: calculating the actual amplitude of the structural vibration on the time sequence by using the time sequence relative displacement change field and the conversion scale factor;
And a frequency calculation module: obtaining the vibration frequency of the structure to be tested through fast Fourier transform according to the time sequence actual displacement field;
the space-frequency conversion method comprises Gabor wave conversion, hilbert conversion and log-Gabor conversion;
The image space feature conversion process of the Gabor wave specifically includes:
(1) Converting the acquired image into a gray characteristic image, and selecting a wavelength and a direction suitable for Gabor according to vibration information of a structure to be detected;
(2) Convolving the Gabor wave with the gray characteristic image in a space domain to obtain a first frequency domain space complex characteristic sequence of the image in a frequency domain, and defining space complex characteristics of adjacent frames as I g (u, v, t) and I g (u, v, t+Δt) respectively, wherein t represents the current moment, Δt represents a time step, and (u, v) is a frequency domain coordinate;
(3) Solving the amplitude of the complex features of the image by using abs (·) operators to obtain the amplitude features of each pixel position:
wherein |· | 2 represents the absolute value;
The division module specifically comprises:
(1) Dynamically selecting the frequency domain space complex characteristics of two frames of images with adjacent time sequences
Wherein A (u, v, t) and A (u, v, t+Δt) respectively correspond to frequency domain magnitudes of different frames, f 0 is frequency, and Δy is relative displacement variation in the y direction;
(2) Processing the phase characteristics of the selected adjacent frame images by utilizing a division operator, deriving through complex integral operation to obtain second frequency domain space complex characteristics, namely
(3) And continuously repeating the time division step along the time sequence direction on the first frequency domain space complex characteristic sequence to obtain a second frequency domain space complex characteristic sequence.
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