CN112697259B - Beam structure modal shape measuring device and method based on combined stripes - Google Patents
Beam structure modal shape measuring device and method based on combined stripes Download PDFInfo
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- CN112697259B CN112697259B CN202011625005.5A CN202011625005A CN112697259B CN 112697259 B CN112697259 B CN 112697259B CN 202011625005 A CN202011625005 A CN 202011625005A CN 112697259 B CN112697259 B CN 112697259B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
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- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
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- G06T7/0004—Industrial image inspection
Abstract
The invention relates to a beam structure modal shape measuring device and method based on combined stripes, the device comprises a beam structure to be measured, a visual sensor, an optical lens, an adjustable bracket and a computer with an image processing module, the surface of the beam structure to be measured is attached with a combined stripe pattern, the visual sensor is installed on the adjustable bracket so as to image the combined stripe pattern on the surface of the beam structure to be measured in real time, the optical lens is installed at the front end of the visual sensor so as to obtain a clear combined stripe image on the surface of the structure by adjusting the optical lens, the visual sensor is connected with the computer through a data connecting line so as to upload acquired image information, and the computer processes and analyzes the acquired image information through the image processing module so as to calculate and obtain vibration information of the beam structure to be measured. The device and the method are beneficial to improving the precision and the efficiency of the measurement of the vibration information of the beam structure, and have simple structure and low realization cost.
Description
Technical Field
The invention belongs to the technical field of visual vibration measurement, and particularly relates to a beam structure modal shape measurement device and method based on combined stripes.
Background
Currently, modal analysis can be divided into computational modal analysis and experimental modal analysis. The calculation mode taking finite element calculation as a main method has been developed and relatively perfect, and has been widely applied in the fields of machines, buildings, aerospace aircrafts, ships, automobiles and the like. However, the test mode analysis is limited by the measurement system and the processing system, and cannot be developed at a high speed. In recent decades, due to the development of computer technology, FFT analyzers, high-speed data acquisition systems, vibration sensors, actuators and other technologies, experimental modal analysis has also been developed and is highly valued by many industrial sectors such as machinery, electric power, construction, water conservancy, aviation, aerospace and the like. For the analysis of the current test mode, the specific natural frequency and the specific damping ratio of the structure can be better measured, and no effective measurement means is available for the mode vibration. Most of measurement methods are that a plurality of displacement sensors are installed on the surface of a structure to be measured, and the modal shape is obtained through vibration information obtained by each displacement sensor. However, such a method often introduces additional mass into the structure to be tested, and the inherent vibration characteristics of the structure are affected. Or an optical vibration measurement system is adopted, and the modal vibration mode of the structure to be measured is obtained through full-field scanning. However, the full-field scanning laser vibration meter is expensive, has strict requirements on the environment, and is not suitable for being applied to actual engineering projects.
Disclosure of Invention
The invention aims to provide a beam structure modal shape measuring device and method based on combined stripes, which are beneficial to improving the precision and efficiency of beam structure vibration information measurement, and have the advantages of simple structure and low implementation cost.
In order to achieve the purpose, the invention adopts the technical scheme that: the utility model provides a beam structure mode vibration type measuring device based on combination stripe, its characterized in that, including the beam structure that awaits measuring, visual sensor, optical lens, adjustable support and the computer that has image processing module, the beam structure surface that awaits measuring is with combination stripe pattern, visual sensor installs on adjustable support to carry out real-time imaging to the combination stripe pattern on the beam structure surface that awaits measuring, optical lens installs in visual sensor front end to obtain the clear combination stripe image in structure surface through adjusting optical lens, visual sensor passes through the data connecting wire and is connected with the computer, the image information who reaches the upload, the computer carries out the processing analysis through image processing module to the image information who gathers, and then calculates the vibration information that obtains the beam structure that awaits measuring.
Furthermore, the shape of the combined stripe pattern is rectangular, the whole pattern is printed on paper to obtain a picture with the combined stripe pattern, and then the picture is attached to the surface of the beam structure to be detected, or the whole pattern is directly sprayed on the surface of the beam structure to be detected without being printed on the paper to be used as a vibration sensor.
Furthermore, the combined stripe pattern is composed of single-density sinusoidal stripes in two different directions, and comprises measuring stripes arranged in the middle and distributed along the width direction and positioning stripes arranged on two sides of the measuring stripes along the length direction, and the distribution directions of the two stripes form an angle of 90 degrees.
Further, the positioning stripes have a period ofaThe measuring stripes have a period ofbSingle density sinusoidal stripes.
The invention also provides a beam structure modal shape measurement method based on the combined stripes, which comprises the following steps:
step S1: designing the size of the combined stripe pattern according to the size of the beam structure to be detected, and attaching or spraying the combined stripe pattern on the surface of the beam structure to be detected;
step S2: installing a vision sensor on an adjustable bracket, adjusting the imaging position of the combined stripe, and adjusting an optical lens to clearly present the pattern of the combined stripe in the center of the vision sensor;
step S3: when the beam structure to be measured is excited to vibrate, the visual sensor collects a combined stripe image of the beam structure to be measured during vibration in real time and uploads the combined stripe image to the computer;
step S4: and the computer processes and analyzes the collected combined fringe image through the image processing module, and calculates and obtains multipoint vibration information of the beam structure to be measured through a method combining positioning and measurement so as to obtain the resonance frequency and the mode shape.
Further, in step S4, the specific step of processing and analyzing the combined fringe image is:
step S41: carrying out interpolation resampling on the positioning stripes on the two sides of each frame of combined stripe image to improve positioning accuracy, then carrying out fast Fourier transform to obtain the frequency spectrum of the positioning stripes, extracting the frequency of the largest component in the frequency spectrum, and filtering out part of noise frequency spectrum;
step S42: performing inverse Fourier transform on the frequency spectrum obtained in the step S41 to obtain wrapping phase information of clear positioning stripes, and performing phase demodulation on the wrapping phase information to obtain unwrapped phase information; the phase information of the positioning stripes corresponds to pixel points of the image one by one, and the positioning of each frame of stripe is realized;
step S43: extracting a measuring stripe at a numerical value phase point from each frame of combined stripe image, processing to obtain the stripe density of each frame of measuring stripe at the phase point, taking the measuring stripe of the first frame as a reference, and performing contrast analysis on the measuring stripe of the first frame and the stripe density of the reference frame to further obtain vibration information of the point on the beam structure to be measured, wherein the vibration information is vertical to the imaging plane direction;
step S44: and processing the measuring stripes of the phase points with different values to obtain multipoint vibration information of the beam structure to be measured, and further obtain the resonance frequency and the mode vibration mode.
Further, in step S43, the time domain displacement vibration signal Δ in the Z direction of the beam structure to be measuredz(t) The calculation method comprises the following steps:
wherein Δz(t) For the beam structure to be measuredtThe Z-direction displacement at a time is,fis the focal length of the optical lens group,Afor structural gauges of beams to be measuredThe actual width of the measuring stripe of the facet,pis the pixel point size of the visual sensor,nfor the reference frame, the length in the stripe image isAThe number of pixels occupied by the measurement stripe of (2),d 0to measure the fringe density in the reference frame fringe image,d(t) Is composed oftThe measured fringe density in the fringe image at time instant.
Compared with the prior art, the invention has the following beneficial effects:
1) the invention is a non-contact measuring method, the quality of the combined stripe pattern can be almost ignored, the combined stripe pattern is attached to or sprayed on the surface of the beam structure to be measured, the interference on the dynamic characteristic of the structure is extremely small, and the extra quality error introduced by the traditional contact sensor can be greatly reduced;
2) the invention can realize the measurement of vibration information of multiple points on the beam structure along the central line by a method combining positioning and measurement through one-time shooting, can identify the resonance frequency and the mode vibration mode, does not need a plurality of sensors, and does not need to scan the beam structure point by point;
3) the invention has simple structure, convenient installation, low realization cost and high measurement precision, and greatly improves the measurement efficiency of the modal vibration mode.
Drawings
Fig. 1 is a schematic structural diagram of an apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a combined stripe pattern according to an embodiment of the present invention.
FIG. 3 is a schematic diagram of a process for locating stripes according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of a processing method for measuring stripes according to an embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the embodiments.
Fig. 1 is a schematic structural diagram of an apparatus according to an embodiment of the present invention. As shown in fig. 1, the invention provides a beam structure modal shape measuring device based on combined fringes, which comprises a beam structure 2 to be measured, a vision sensor 4, an optical lens 3, an adjustable bracket 5 and a computer 6 with an image processing module. The surface of the beam structure 2 to be measured is attached with a combined stripe pattern 1, the vision sensor 4 is installed on the adjustable support 5 to perform real-time imaging on the combined stripe pattern on the surface of the beam structure to be measured, and the optical lens 3 is installed at the front end of the vision sensor 4 to obtain a clear combined stripe image on the surface of the structure by adjusting the optical lens. The vision sensor 4 is connected with the computer 6 through a data connecting line. When the structure is excited to vibrate, the combined fringe pattern on the surface of the structure will vibrate accordingly. The vision sensor 4 collects a combined stripe image in vibration in real time and uploads the collected image information, and the computer 6 processes and analyzes the collected image information through the image processing module and further calculates to obtain vibration information of the beam structure to be measured.
Fig. 2 is a schematic diagram of the combined stripe pattern in the present embodiment. In this embodiment, the combined stripe pattern has a rectangular shape, and the length of the combined stripe pattern is usually several times the width of the combined stripe pattern, and the combined stripe pattern can be set according to the size of the beam structure to be measured. The whole pattern is printed on paper to obtain a picture with a combined stripe pattern, and then the picture is attached to the surface of the beam structure to be detected, or the whole pattern is directly sprayed on the surface of the beam structure to be detected without being printed on the paper to be used as a vibration sensor. The combined stripe pattern is composed of single-density sine stripes in two different directions, and comprises measuring stripes arranged in the middle and distributed along the width direction and positioning stripes arranged on two sides of the measuring stripes along the length direction, and the distribution directions of the two stripes form an angle of 90 degrees. The positioning stripes have a period ofaThe measuring stripes have a period ofbThe density of the two kinds of the sinusoidal stripes can be designed into a proper value according to the actual measurement requirement.
The invention also provides a beam structure modal shape measuring method based on the measuring device, which comprises the following steps:
step S1: and designing the size of the combined stripe pattern according to the size of the beam structure to be detected, and attaching or spraying the combined stripe pattern on the surface of the beam structure to be detected.
Step S2: and installing the visual sensor on the adjustable bracket, adjusting the imaging position of the combined stripe, and adjusting the optical lens to clearly present the combined stripe pattern in the center of the visual sensor.
Step S3: when the beam structure to be measured is excited to vibrate, the visual sensor collects the combined stripe image of the beam structure to be measured in real time and uploads the combined stripe image to the computer.
Step S4: and the computer processes and analyzes the collected combined fringe image through the image processing module, and calculates and obtains multipoint vibration information of the beam structure to be measured through a method combining positioning and measurement so as to obtain the resonance frequency and the mode shape.
Fig. 3 is a schematic diagram of a processing procedure for positioning stripes in this embodiment. As shown in fig. 3(a), to locate a part of the picture of the stripe, a single-line image of the located stripe indicated by an arrow is extracted, and stripe grayscale information as shown in fig. 3(b) is obtained. However, the streak information captured by the vision sensor 4 may have a deviation in value and may include other frequency information, which requires preprocessing. Processing the positioning stripes by using Fourier transform profilometry: firstly, carrying out interpolation resampling on positioning stripes so as to improve the positioning precision; secondly, performing fast Fourier transform on the interpolated positioning stripe image to obtain a frequency spectrum of the positioning stripe; then, extracting the frequency of the maximum component in the frequency spectrum, and filtering some noise frequency spectrums; then, carrying out inverse Fourier transform on the frequency spectrum to obtain clear wrapping phase information of the positioning stripes; finally, the unwrapped phase information of the positioning fringe is solved to obtain a phase curve with a single trend, as shown in fig. 3 (c). Each image can obtain a similar phase curve, and the phase point of a certain numerical value is taken for each fringe phase curve, so that the measuring fringe where the phase point is located can be positioned. By taking the measuring stripes of different numerical phase points for processing, the multipoint vibration information on the beam structure can be measured. The specific treatment steps are as follows:
step S41: carrying out interpolation resampling on the positioning stripes on the two sides of each frame of combined stripe image to improve positioning accuracy, then carrying out fast Fourier transform to obtain the frequency spectrum of the positioning stripes, extracting the frequency of the largest component in the frequency spectrum, and filtering out part of noise frequency spectrum;
step S42: performing inverse Fourier transform on the frequency spectrum obtained in the step S41 to obtain clear wrapped phase information of the positioning stripes, and performing phase demodulation on the wrapped phase information to obtain unwrapped phase information to obtain a phase curve with a single trend; the phase information of the positioning stripes corresponds to pixel points of the image one by one, and the positioning of each frame of stripe is realized;
step S43: extracting a measuring stripe at a numerical value phase point from each frame of combined stripe image, processing to obtain the stripe density of each frame of measuring stripe at the phase point, taking the measuring stripe of the first frame as a reference, and performing contrast analysis on the measuring stripe of the first frame and the stripe density of the reference frame to further obtain vibration information of the point on the beam structure to be measured, wherein the vibration information is vertical to the imaging plane direction;
step S44: and processing the measuring stripes of the phase points with different values to obtain multipoint vibration information of the beam structure to be measured, and further obtain the resonance frequency and the mode vibration mode.
Fig. 4 is a schematic view of a measuring method for measuring the fringe in the present embodiment. In the present embodiment, the measuring stripe 1 is located in the middle portion of the combined stripe, and is pasted or sprayed on the surface of the structure to be measured. The stripe pattern 1 obtains a clear stripe image on the vision sensor 4 by adjusting the optical lens 3. When the structure to be measured vibrates, the distance between the structure to be measured and the optical lens 3DChanges occur, which in turn causes changes in the fringe image obtained by the vision sensor 4. By positioning the positioning fringes in fig. 3, the measurement fringe image of a single row of pixels where a certain value phase point of different images is located is extracted, the distribution of the fringes can be obtained, the fourier transform (FFT) is performed on the measurement fringes of the phase point of all each frame of image, and the accurate fringe density can be obtained by applying the energy center-of-gravity spectrum correction algorithm (SCCM)d(t) And the density of the stripes when the beam structure is at restd 0And as a reference frame, reflecting the vibration information of the beam structure to be measured through the change between the stripe densities. Time domain displacement vibration signal delta of beam structure to be measuredz(t) The calculation method comprises the following steps:
wherein Δz(t) For the beam structure to be measuredt The displacement at a moment in time is,fis the focal length of the optical lens group,Afor measuring the actual width of the stripe on the surface of the beam structure to be measured,pis the size of the pixel points of the visual sensor,nfor the reference frame, the length in the stripe image isAThe number of pixels occupied by the measurement stripe of (2),d 0to measure the fringe density in the reference frame fringe image,d(t) Is composed oftThe measured fringe density in the fringe image at time instant.
The above are preferred embodiments of the present invention, and all changes made according to the technical scheme of the present invention that produce functional effects do not exceed the scope of the technical scheme of the present invention belong to the protection scope of the present invention.
Claims (3)
1. A measuring method of a beam structure modal shape measuring device based on combined stripes is characterized by comprising a beam structure to be measured, a visual sensor, an optical lens, an adjustable support and a computer with an image processing module, wherein the surface of the beam structure to be measured is attached with a combined stripe pattern, the visual sensor is installed on the adjustable support so as to image the combined stripe pattern on the surface of the beam structure to be measured in real time, the optical lens is installed at the front end of the visual sensor so as to obtain a clear combined stripe image on the surface of the structure by adjusting the optical lens, the visual sensor is connected with the computer through a data connecting wire so as to upload acquired image information, and the computer processes and analyzes the acquired image information through the image processing module so as to calculate and obtain vibration information of the beam structure to be measured;
the combined stripe pattern is rectangular, and comprises two single-density sinusoidal stripes in different directions, including measuring stripe arranged in the middle part along the width direction and positioning stripe arranged on the two sides along the length direction, wherein the distribution directions of the two stripes form an angle of 90 DEG, and the positioning stripe has a period ofaSingle density of sinusoidal stripes, said measuringThe measuring stripe has a period ofbSingle density sinusoidal stripes of (a);
the beam structure modal shape measuring method based on the measuring device comprises the following steps:
step S1: designing the size of the combined stripe pattern according to the size of the beam structure to be detected, and attaching or spraying the combined stripe pattern on the surface of the beam structure to be detected;
step S2: installing a vision sensor on an adjustable bracket, adjusting the imaging position of the combined stripe, and adjusting an optical lens to clearly present the pattern of the combined stripe in the center of the vision sensor;
step S3: when the beam structure to be measured is excited to vibrate, the visual sensor collects a combined stripe image of the beam structure to be measured during vibration in real time and uploads the combined stripe image to the computer;
step S4: the computer processes and analyzes the collected combined stripe image through the image processing module, and calculates and obtains multipoint vibration information of the beam structure to be measured through a method of combining positioning and measurement, so as to obtain resonance frequency and modal shape;
in step S4, the specific steps of processing and analyzing the combined fringe image are as follows:
step S41: carrying out interpolation resampling on the positioning stripes on the two sides of each frame of combined stripe image to improve positioning accuracy, then carrying out fast Fourier transform to obtain the frequency spectrum of the positioning stripes, extracting the frequency of the largest component in the frequency spectrum, and filtering out part of noise frequency spectrum;
step S42: performing inverse Fourier transform on the frequency spectrum obtained in the step S41 to obtain wrapping phase information of clear positioning stripes, and performing phase demodulation on the wrapping phase information to obtain unwrapped phase information; the phase information of the positioning stripes corresponds to pixel points of the image one by one, and the positioning of each frame of stripe is realized;
step S43: extracting a measuring stripe at a numerical value phase point from each frame of combined stripe image, processing to obtain the stripe density of each frame of measuring stripe at the phase point, taking the measuring stripe of the first frame as a reference, and performing contrast analysis on the measuring stripe of the first frame and the stripe density of the reference frame to further obtain vibration information of the point on the beam structure to be measured, wherein the vibration information is vertical to the imaging plane direction;
step S44: and processing the measuring stripes of the phase points with different values to obtain multipoint vibration information of the beam structure to be measured, and further obtain the resonance frequency and the mode vibration mode.
2. The method as claimed in claim 1, wherein the entire pattern is printed on paper to obtain a picture with the pattern of the combined stripe, and the picture is attached to the surface of the beam structure to be measured, or the entire pattern is directly sprayed on the surface of the beam structure to be measured without being printed on paper to serve as a vibration sensor.
3. The method for measuring the beam structure mode-shape measuring device based on the combined fringe as claimed in claim 1, wherein in step S43, the time-domain displacement vibration signal Δ in the Z direction of the beam structure to be measuredz(t) The calculation method comprises the following steps:
wherein Δz(t) For the beam structure to be measuredtThe Z-direction displacement at a time is,fis the focal length of the optical lens group,Afor measuring the actual width of the stripe on the surface of the beam structure to be measured,pis the pixel point size of the visual sensor,nfor the reference frame, the length in the stripe image isAThe number of pixels occupied by the measurement stripe of (2),d 0to measure the fringe density in the reference frame fringe image,d(t) Is composed oftThe measured fringe density in the fringe image at time instant.
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