CN109341548B - Three-dimensional vibration vision measurement system and method based on variable density stripes - Google Patents
Three-dimensional vibration vision measurement system and method based on variable density stripes Download PDFInfo
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Abstract
The invention relates to a three-dimensional vibration vision measurement system and a method based on variable density stripes. The three-dimensional vibration measurement method comprises the following steps: installing variable density stripes on the surface of the vibration structure to be measured; installing a visual imaging and processing system on a fixed support, and adjusting the imaging position of the variable-density stripes and the parameters of an imaging lens to enable the variable-density stripes to be imaged at the central position of an area-array camera; and starting a measurement mode of the visual imaging and processing system to measure the vibration of the vibration structure. The invention comprises an algorithm and a flow for processing the variable density stripe sequence, and can simply and efficiently extract the three-dimensional displacement information of the structure from the variable density stripe sequence.
Description
Technical Field
The invention relates to the technical field of structural vision vibration measurement, in particular to a three-dimensional vibration vision measurement system and method based on variable-density stripes.
Background
Machine vision measurement technology is a new measurement technology, and is concerned by more and more researchers with the characteristics of non-contact, high efficiency, high precision, no load effect and the like. Moreover, with the development of digital imaging technology and image processing technology, the imaging resolution and imaging speed of the area-array camera are greatly improved, so that the machine vision measurement technology is rapidly developed. The method generally adopts an area-array camera to continuously acquire and image target patterns or natural features on the surface of a vibrating structure, and then adopts different image processing technologies to extract and measure physical parameters such as vibration, deformation, displacement and the like of the measured structure.
At present, many researchers adopt black-and-white patterns or speckle patterns with clear edges, which are composed of regular patterns such as circles and squares, as target patterns to cover the surface of a structure, then use an area-array camera to image the structure, and then use an image contrast tracking algorithm, a template matching algorithm, an edge detection technology, a two-dimensional digital image correlation algorithm and the like to realize the measurement of two-dimensional dynamic displacement of the structure parallel to the plane of an area-array sensor. These current measurement methods suffer from several disadvantages: 1) the image processing algorithm adopted when extracting the two-dimensional displacement information of the structure in the image has relatively large calculated amount, has higher requirements on the processing capability of a processing module, and is difficult to realize real-time measurement; 2) the current monocular vision measuring system can only realize two-dimensional dynamic displacement measurement parallel to the plane of the area array sensor generally, and a binocular vision measuring system is needed to realize three-dimensional measurement; 3) the current vision measurement system needs to calibrate the space coordinate of the camera, the actual calibration steps are complex, and the measurement accuracy is influenced by the parameter calibration precision.
Disclosure of Invention
In view of this, the present invention provides a three-dimensional vibration vision measurement system and method based on variable density stripes, which achieve synchronous measurement of three-dimensional vibration of a structure, and have simple measurement device and high measurement efficiency.
In order to achieve the purpose, the invention adopts the following technical scheme:
a three-dimensional vibration vision measurement system based on variable density stripes comprises variable density stripes which are used as sensors for sensing three-dimensional displacement of a structural space and are arranged on the surface of a structure to be measured, and a vision imaging and processing system which is used for imaging and processing the variable density stripes covering the surface of the vibration structure to be measured in real time; the visual imaging and processing system comprises a visual imaging camera, an embedded control system, an image storage and processing module, a display and interaction module and a power supply module; the embedded control system is respectively connected with the visual imaging camera, the image storage and processing module, the display and interaction module and the power supply module.
Furthermore, the variable density stripe is rectangular in shape, and the length and the width of the variable density stripe can be set according to the size of the vibration structure to be measured.
Furthermore, the stripes of the rectangular variable-density stripes along the length direction are sine stripes with constant stripe density, the stripe period number of the sine stripes along the width direction changes in a quadratic function mode, and the actual width of each row of the stripes is equal.
Further, the quadratic function is specifically:
whereinaThe number of fringe periods at the symmetric center in the width direction of the variable density fringe,Mto generate the total number of pixel points in the width direction in the variable density stripe image,mis a pixel coordinate variable in the width direction,the number of fringe periods for different pixel rows in the width direction.
Furthermore, the symmetric center of the rectangular variable-density stripe periodic density quadratic variation function is positioned at the symmetric center of the rectangular width direction.
Further, the measuring method of the three-dimensional vibration vision measuring system based on the variable density stripes is characterized by comprising the following steps:
step S1: installing variable-density stripes on the surface of the vibration structure to be detected;
step S2: installing the visual imaging and processing system on a fixed support, starting an imaging adjustment mode, and adjusting the imaging position of the variable-density stripes and the parameters of a lens of a visual imaging camera to enable the variable-density stripes to be imaged at the central position of the visual imaging camera;
step S3: according to the vibration characteristics of the vibration structure to be detected, the imaging frame rate of the imaging variable-density stripes is set, the measurement mode of the visual imaging and processing system is started, the vibration of the vibration structure to be detected is measured, and the three-dimensional time domain displacement signal of the vibration structure to be detected is obtained.
Further, the step S3 of measuring the vibration of the vibration structure to be measured specifically includes:
step S31: obtaining a fringe period density change curve of each frame of fringe image along the width direction;
step S32: obtaining a slope curve of each frame of fringe period density change curve, obtaining an accurate coordinate value with a width direction slope value of zero through interpolation by a linear interpolation method, taking the coordinate value of the first frame as a reference point, and calculating a time domain displacement curve of the vibration structure to be measured along the vertical direction by adopting a vertical direction displacement calculation formula;
step S33: the accurate coordinate value with the slope value of zero is brought into a stripe period density change curve again, a stripe density value of a stripe width direction symmetric center position is obtained through interpolation, the density value of a first frame is used as a reference point, and a time domain displacement curve of the vibration structure to be detected along the direction of the imaging optical axis is calculated by adopting a displacement calculation formula along the direction of the imaging optical axis;
step S34: extracting a fringe signal of each frame of which the fringe width direction slope value is a zero coordinate line, taking the fringe signal of a first frame as a reference fringe, performing cross correlation on the fringe signal at the symmetrical center of each frame and the reference fringe, obtaining an accurate coordinate value of a maximum peak value of a related sequence by an interpolation method, taking the maximum peak value coordinate of an autocorrelation sequence of the reference fringe as a reference point, and finally calculating a time domain displacement curve of the vibration structure to be measured along the horizontal direction by adopting a horizontal direction displacement calculation formula;
step S35: and transmitting the obtained three-dimensional time domain displacement signal to a display and interaction module for real-time display.
Further, the calculation formula of the displacement of the vibration structure to be measured along the vertical direction is as follows:
whereinTo be tested vibrating structuretThe displacement in the vertical direction is at the moment,Lfor the actual effective length in the length direction of the variable density stripe,is a symmetric center line of the width direction of the variable density stripeThe number of pixel points covered by the fringe signal in the imaging sensor of the visual imaging camera,is composed oftThe number of pixel points on the imaging sensor that the symmetric center line of the time-varying density fringe is offset relative to the symmetric center line of the reference fringe,andrespectively, a reference frame andtand the density value of the stripe at the position of the symmetrical center line of the time-varying density stripe.
Further, the mathematical relationship of the displacement of the vibration structure to be measured along the direction of the imaging optical axis is as follows:
whereinTo be tested vibrating structuretThe displacement in the direction of the optical axis of the imaging at the moment,Dis the initial imaging object distance.
Further, the mathematical relationship of the displacement of the vibration structure to be measured along the horizontal direction is as follows:
whereinIs composed oftThe displacement in the horizontal direction at the moment,is composed oftThe number of pixel points of which the centers of the stripes at the symmetrical center lines of the time-varying density stripes are offset relative to the reference point.
Compared with the prior art, the invention has the following beneficial effects:
(1) the vision three-dimensional measurement system based on the variable density stripes has simple principle and low cost of the variable density stripes, and can realize remote structure three-dimensional vibration measurement;
(2) the variable density stripe signal processing method has the advantages that the variable density stripe signal processing steps are simple, the algorithm computation amount is small, the computation amount is greatly reduced compared with the current algorithm computation amount based on two-dimensional image correlation and two-dimensional image matching, the performance requirement on a processor can be reduced, and the hardware cost is reduced;
(3) the invention can realize the synchronous measurement of the three-dimensional vibration displacement, and has higher measurement capability and efficiency compared with the current vision measurement system which can only realize the vibration measurement parallel to the imaging camera sensor plane.
Drawings
FIG. 1 is a schematic diagram of a system measurement according to an embodiment of the present invention.
FIG. 2 is a design diagram of variable density stripes and an illustrative process flow diagram according to an embodiment of the present invention. Wherein (a) is a variable density stripe form illustration; (b) the variation curve of the stripe period density along the width direction of the stripe in the graph (a); (c) the slope of the variation curve of the stripe density in the graph (b) is shown.
FIG. 3 is a flow chart of three-dimensional displacement calculation according to an embodiment of the present invention.
FIG. 4 is a schematic view of a visual imaging and processing system according to an embodiment of the invention.
In the figure, 1-variable density stripe, 2-vibration structure to be measured, 3-visual imaging and processing system, 4-display and interaction module, and 5-fixed support.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
As shown in fig. 1, the present embodiment provides a three-dimensional vibration vision measuring system and method based on variable density stripes, which includes a variable density stripe 1, a vibration structure 2, a vision imaging and processing system 3, a display and interaction module 4, and a fixing bracket 5. The variable density stripe 1 is used as a sensor to cover the surface of the vibrating structure 2, and the visual imaging and processing system 3 is fixed on the fixed bracket 5. The variable density stripes 1 vibrate along with the vibration of the vibrating structure 2, and the variable density stripes are acquired and processed in real time by adopting a visual imaging and processing system 3 in the vibrating process to obtain a time domain three-dimensional displacement curve of the vibrating structure 2 and are displayed in real time in a display and interaction module.
In this embodiment, the imaging position and the imaging fringe density of the variable-density fringe in the area array imaging sensor of the visual imaging and processing system will change with the displacement of the structure in different directions; when the structure is displaced along the direction of the imaging optical axis, the stripe density value at the symmetric center in the width direction of the variable density stripe changes, and displacement information of the structure along the direction of the imaging optical axis can be obtained through the change of the stripe density value at the position; the fringe density of each row of the variable-density fringes synchronously changes along with the displacement of the structure along the direction of the imaging optical axis, namely, the fringe density synchronously decreases along with the increase of the imaging object distance and synchronously increases along with the decrease of the imaging object distance, so that the fringe period density change rule of the variable-density fringes along the width direction still changes in a quadratic function manner; the stripe period density change curve of the variable density stripe image is obtained by carrying out spectrum analysis on stripe signals of the stripe image along the length direction, namely, the period density value of the stripe is determined by obtaining the frequency value of the sinusoidal stripe signal of each row, and then the period density curve of the variable density stripe along the width direction is obtained; the position of the symmetrical center in the width direction of the variable density stripe can be determined by solving a zero value coordinate of a slope curve of the periodic density curve; the density value of the stripe positioned at the symmetrical center of the width direction of the variable density stripe is equal to the value of the zero coordinate position of the slope curve of the periodic density curve; when the structure is displaced along the vertical direction, the imaging position of the symmetrical center of the variable-density stripe in the width direction in the area array sensor is changed, and displacement information of the structure in the vertical direction can be obtained through the change of the central position; when the structure has displacement along the horizontal direction, the symmetrical center of the variable density stripe in the length direction changes at the imaging position of the area array sensor, and the displacement information of the structure in the horizontal direction can be obtained through the change of the central position; the symmetric center of the variable density stripe in the length direction can be determined by the central position of a stripe signal at the symmetric center of the variable density stripe in the width direction; the central position of the symmetric central stripe signal in the width direction of the variable-density stripe can be determined by the maximum peak position coordinate of the one-dimensional cross-correlation sequence of the position stripe signal and the reference stripe signal.
FIG. 2 is a design diagram of variable density stripes and an illustrative process flow diagram according to an embodiment of the present invention. Wherein (a) is a variable density stripe form explanatory diagram, as shown in the diagram (a), the variable density stripe 1 is rectangular in shape, and the length and the width of the variable density stripe can be set according to the size of a structure to be measured; the stripes of the rectangular variable-density stripes 1 along the length direction are sine stripes with constant stripe density; the number of fringe periods of the sinusoidal fringes along the width direction varies as a quadratic function, and the actual width of each row of fringes is equal toLTherefore, the periodic density of the variable density stripe 1 along the width direction is changed in a quadratic function manner; the symmetry center of the stripe period density quadratic variation function of the variable density stripe 1 is positioned at the symmetry center position in the width direction of the rectangle, namely shown by a dotted line in the figure. In the measurement process, the frequency spectrum analysis can be performed on each row of stripes of the stripe pattern to obtain a periodic density change curve of each frame of stripes along the width direction, as shown in the diagram (b). The obtained periodic density variation curve is then derived to obtain a slope curve of the density variation curve, as shown in fig. (c). Because the stripe period density change curve is a quadratic function, the derivative of the stripe period density change curve is a linear function, and the accurate coordinate value of which the gradient of the variable density curve is zero can be obtained through linear interpolation, namely the position of the symmetrical center in the width direction of each frame of variable density stripe can be determined.
FIG. 3 is a flow chart of three-dimensional displacement calculation according to an embodiment of the present invention. As shown in figure 3 of the drawings,
step S31: obtaining a fringe period density change curve of each frame of fringe image along the width direction;
step S32: and solving a slope curve of each frame of fringe period density change curve, interpolating by a linear interpolation method to obtain an accurate coordinate value with a width direction slope value of zero, taking the coordinate value of the first frame as a reference point, and calculating a time domain displacement curve of the structure along the vertical direction by adopting a vertical direction displacement calculation formula. The calculation formula of the displacement of the structure along the vertical direction is as follows:
whereinTo be tested vibrating structuretThe displacement in the vertical direction is at the moment,Lfor the actual effective length in the length direction of the variable density stripe,the number of pixel points covered by the stripe signal of the symmetric central line in the width direction of the variable-density stripe in an imaging sensor of a visual imaging camera,is composed oftThe number of pixel points on the imaging sensor that the symmetric center line of the time-varying density fringe is offset relative to the symmetric center line of the reference fringe,andrespectively, a reference frame andtand the density value of the stripe at the position of the symmetrical center line of the time-varying density stripe.
Step S33: and substituting an accurate coordinate value with a slope value of zero into a stripe period density change curve again, obtaining a stripe density value of a symmetric center position in the stripe width direction through interpolation, taking the density value of the first frame as a reference point, and calculating a time domain displacement curve of the structure in the imaging optical axis direction by adopting a displacement calculation formula in the imaging optical axis direction. The mathematical relation of the displacement of the vibration structure to be measured along the direction of the imaging optical axis is as follows:
whereinTo be tested vibrating structuretThe displacement in the direction of the optical axis of the imaging at the moment,Dis the initial imaging object distance.
Step S34: and extracting a fringe signal of each frame with a zero coordinate slope value in the width direction of the fringe, taking the fringe signal of the first frame as a reference fringe, performing cross correlation on the fringe signal at the symmetrical center of each frame and the reference fringe, obtaining an accurate coordinate value of the maximum peak value of the correlation sequence by an interpolation method, taking the maximum peak value coordinate of the autocorrelation sequence of the reference fringe as a reference point, and calculating a time domain displacement curve of the structure along the horizontal direction by adopting a horizontal direction displacement calculation formula. The mathematical relation of the displacement of the vibration structure to be measured along the horizontal direction is as follows:
whereinIs composed oftThe displacement in the horizontal direction at the moment,is composed oftThe number of pixel points of which the centers of the stripes at the symmetrical center lines of the time-varying density stripes are offset relative to the reference point.
Step S35: and transmitting the three-dimensional time domain displacement signal to a display and interaction module for real-time display.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (8)
1. A three-dimensional vibration vision measurement system based on variable density stripes is characterized in that: the system comprises variable density stripes arranged on the surface of a structure to be detected and a visual imaging and processing system for imaging and processing the variable density stripes covering the surface of the vibrating structure to be detected in real time; the visual imaging and processing system comprises a visual imaging camera, an embedded control system, an image storage and processing module, a display and interaction module and a power supply module; the embedded control system is respectively connected with the visual imaging camera, the image storage and processing module, the display and interaction module and the power supply module; the variable density stripes are rectangular in shape, and the length and the width of the variable density stripes can be set according to the size of the vibration structure to be detected; the stripes of the rectangular variable-density stripes along the length direction are sine stripes with constant stripe density, the stripe period number of the sine stripes along the width direction is changed in a quadratic function mode, and the actual width of each row of the stripes is equal.
2. The variable density fringe-based three-dimensional vibratory vision measuring system of claim 1, wherein: the quadratic function is specifically:
wherein a is the number of fringe periods at the symmetric center of the variable density fringe in the width direction, M is the total number of pixel points in the width direction when the variable density fringe image is generated, M is the pixel coordinate variable in the width direction, and d (M) is the number of fringe periods of different pixel rows in the width direction.
3. The variable density fringe-based three-dimensional vibratory vision measuring system of claim 1, wherein: the symmetric center of the rectangular variable-density stripe periodic density quadratic variation function is positioned at the symmetric center position in the width direction of the rectangle.
4. The measuring method of the three-dimensional vibration vision measuring system based on the variable density stripes according to any one of claims 1-3, characterized by comprising the following steps:
step S1: installing variable-density stripes on the surface of the vibration structure to be detected;
step S2: installing the visual imaging and processing system on a fixed support, starting an imaging adjustment mode, and adjusting the imaging position of the variable-density stripes and the parameters of a lens of a visual imaging camera to enable the variable-density stripes to be imaged at the central position of the visual imaging camera;
step S3: according to the vibration characteristics of the vibration structure to be detected, the imaging frame rate of the imaging variable-density stripes is set, the measurement mode of the visual imaging and processing system is started, the vibration of the vibration structure to be detected is measured, and the three-dimensional time domain displacement signal of the vibration structure to be detected is obtained.
5. The method of claim 4, wherein the measuring method comprises: the step S3 of measuring the vibration of the vibration structure to be measured specifically includes:
step S31: obtaining a fringe period density change curve of each frame of fringe image along the width direction;
step S32: obtaining a slope curve of each frame of fringe period density change curve, obtaining an accurate coordinate value with a width direction slope value of zero through interpolation by a linear interpolation method, taking the coordinate value of the first frame as a reference point, and calculating a time domain displacement curve of the vibration structure to be measured along the vertical direction by adopting a vertical direction displacement calculation formula;
step S33: the accurate coordinate value with the slope value of zero is brought into a stripe period density change curve again, a stripe density value of a stripe width direction symmetric center position is obtained through interpolation, the density value of a first frame is used as a reference point, and a time domain displacement curve of the vibration structure to be detected along the direction of the imaging optical axis is calculated by adopting a displacement calculation formula along the direction of the imaging optical axis;
step S34: extracting a fringe signal of each frame of which the fringe width direction slope value is a zero coordinate line, taking the fringe signal of a first frame as a reference fringe, performing cross correlation on the fringe signal at the symmetrical center of each frame and the reference fringe, obtaining an accurate coordinate value of a maximum peak value of a related sequence by an interpolation method, taking the maximum peak value coordinate of an autocorrelation sequence of the reference fringe as a reference point, and finally calculating a time domain displacement curve of the vibration structure to be measured along the horizontal direction by adopting a horizontal direction displacement calculation formula;
step S35: and transmitting the obtained three-dimensional time domain displacement signal to a display and interaction module for real-time display.
6. The method of claim 5, wherein the measuring method comprises: the displacement calculation formula of the vibration structure to be measured along the vertical direction is as follows:
wherein, Deltay (t) is the displacement of the vibration structure to be measured in the vertical direction at the moment t, L is the actual effective length of the variable density stripe in the length direction, and NLThe number of pixel points covered by the stripe signal of the symmetric center line in the width direction of the variable density stripe in an imaging sensor of a visual imaging camera is delta m (t), the number of the pixel points of the symmetric center line of the variable density stripe on the imaging sensor at the moment t, which is deviated relative to the symmetric center line of the reference stripe, drAnd d (t) the fringe density values of the fringes at the positions of the symmetric center lines of the variable density fringes at the reference frame and the time t respectively.
7. The method of claim 5, wherein the measuring method comprises: the mathematical relation of displacement of the vibration structure to be detected along the direction of the imaging optical axis is as follows:
wherein, Δ x (t) is the displacement of the vibrating structure to be detected in the imaging optical axis direction at the moment t, and D is the initial imaging object distance; drAnd d (t) the fringe density values of the fringes at the positions of the symmetric center lines of the variable density fringes at the reference frame and the time t respectively.
8. The method of claim 5, wherein the measuring method comprises: the mathematical relation of the displacement of the vibration structure to be measured along the horizontal direction is as follows:
wherein, Δ z (t) is the displacement in the horizontal direction at the time t, and Δ n (t) is the number of pixel points of the deviation of the fringe center at the symmetrical center line of the variable density fringe at the time t relative to the reference point; n is a radical ofLThe number of pixel points covered by stripe signals of a symmetric center line in the width direction of the variable-density stripe in an imaging sensor of a visual imaging camera; drAnd d (t) the fringe density values of the fringes at the positions of the symmetric center lines of the variable density fringes at the reference frame and the time t respectively.
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