CN116952357A - Spectral imaging visual vibration measurement system and method based on combination of line-plane cameras - Google Patents
Spectral imaging visual vibration measurement system and method based on combination of line-plane cameras Download PDFInfo
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Abstract
A spectroscopic imaging visual vibration measurement system and method based on line-plane camera combination belong to the technical field of visual image vibration detection. The invention acquires high-frequency vibration images and low-frequency vibration images through synchronously controlling the linear array camera and the area array camera, thereby widening the vibration frequency measurement range of the system; the large visual field range of the area array camera is used for providing rough position basis for positioning targets and measuring targets of the linear array camera, so that the operation difficulty of a linear array vision system is reduced; for a two-dimensional image with low frequency and large amplitude vibration, the real edges in the image can be identified as much as possible by adopting a Canny algorithm; for a one-dimensional image with high frequency and small amplitude vibration, adopting a linear fitting method based on a gradient operator, and performing accurate fitting after coarse positioning to realize accurate positioning of the edges of the sub-pixels in the edge transition section of the one-dimensional image. The invention is suitable for the measurement field, expands the frequency range of visual vibration measurement and improves the subpixel measurement accuracy of the system.
Description
Technical Field
The invention relates to a spectral imaging visual vibration measurement system and a spectral imaging visual vibration measurement method based on combination of line-plane cameras, and belongs to the technical field of visual image vibration detection.
Background
In industrial production, state monitoring and fault diagnosis of mechanical equipment are important works for ensuring normal operation of the equipment. When the equipment runs at a high speed, vibration phenomenon is unavoidable, and in order to monitor the running state of the equipment, electrical measurement and optical measurement are often used in engineering application to obtain the vibration parameters of the equipment. In engineering application, vibration measurement by an electrical measurement method usually adopts a piezoelectric or MEMS sensor to measure vibration acceleration of the tested equipment, displacement change condition is obtained by double integration of measurement results, and frequency domain analysis is further carried out to determine vibration frequency. An electrical measurement system such as an accelerometer is required to be installed on the surface of tested equipment, the vibration part can bear load to influence original vibration, and meanwhile, a calculation method of acceleration double integral can generate larger accumulated errors which cannot be eliminated by the system when the vibration amplitude is larger.
Laser and vision based measurement techniques are the most common method for obtaining the more widely used photometry. Laser doppler vibrometer is expensive and takes a lot of measuring time for a large measuring target, and its measuring accuracy depends largely on the reflecting ability of the measured object surface, and if the measuring surface is not ideal, the measuring system usually shows poor measuring accuracy. The visual vibration measuring method is to acquire two-dimensional or three-dimensional vibration images of a target through a visual camera, acquire displacement changes of geometric features of the target from a photographic image sequence and further measure vibration information (application numbers: 201410471049.5 and CN 202211135587.8), and has the characteristics of high robustness and high precision. However, in visual vibration measurement method applications, higher vibration amplitude measurement accuracy often requires high resolution. Thus, there are the following disadvantages: 1) In order to obtain high amplitude measurement precision, the area array vision system needs higher resolution, and at the moment, the transmission performance of the system is severely limited, and the exposure shooting acquisition rate is extremely limited; 2) The high-frequency vibration target or the high-frequency component of the target vibration cannot be effectively collected and analyzed by the area array vision system.
For high frequency vibratory measurement targets, a linear vision system is one of the more applicable solutions. Unlike an area camera, a line camera is composed of one or more lines of photosensitive elements, so that a line vision system is hardly affected by a transmission rate, and an image can be acquired at an extremely high sampling frequency while the image is high-resolution. Although linear cameras have significant advantages in terms of resolution and acquisition frequency, these linear camera-based vision vibration measuring systems also have the following drawbacks: 1) Compared with the calibration method of the area array camera, the calibration process of the linear array camera is more complex, the 2D plane target is usually controlled by means of a precision displacement platform, the operation difficulty of the calibration process is high, and the calibration precision is directly influenced by the precision of the platform movement; 2) The linear array camera has extremely small imaging visual field, and the low-frequency large-amplitude motion of the plane easily spans the vertical visual field range of the linear array camera, so that a measurement target is lost, therefore, the general monocular linear array vision system is more suitable for measuring a one-dimensional dynamic target moving in the imaging direction of the camera, and the application scene requirement is relatively strict; 3) In engineering application, when the linear array camera system measures two-dimensional plane motion, the object to be measured or the linear array camera must be matched with scanning motion, vibration generated by motor motion and speed change in the starting and stopping process, and particularly, errors of a mechanical transmission part can influence the measurement accuracy of the second dimension.
Disclosure of Invention
Aiming at the following defects of the prior visual vibration measuring system: 1) The area array vision system is affected by the data transmission performance, the image acquisition frame rate and the image resolution are mutually restricted, high-frequency vibration components of a target cannot be effectively acquired and analyzed, and the amplitude measurement precision and the measurement range of the system are very limited; 2) The linear array vision system can realize frequency measurement of medium-high frequency vibration targets, but the linear array camera has small vertical imaging field of view, few vibration measurement application scenes, complex calibration process, high operation difficulty and larger influence of scanning motion on measurement accuracy. The invention mainly aims to provide a spectroscopic imaging visual vibration measurement system and a spectroscopic imaging visual vibration measurement method based on combination of a line-plane camera, which are based on an optical imaging structure combined with a double spherical mirror and unpolarized spectroscopic imaging.
The invention aims at realizing the following technical scheme:
the invention discloses a spectral imaging visual vibration measurement system based on combination of a line-plane camera, which comprises an imaging spherical primary mirror, an imaging spherical secondary mirror, a spectral prism, an area array visual system, a line array visual system, a data cable and a computer. The imaging spherical primary mirror, the imaging spherical secondary mirror and the beam splitting prism are coaxially arranged in sequence; the linear array vision system and the area array vision system are respectively arranged on two sides of emergent light of the beam splitting prism, optical axes are mutually perpendicular, the linear array vision system and the beam splitting prism transmit the emergent light and are coaxially arranged, and the optical axes of the area array vision system and the beam splitting prism reflect the emergent light and are coaxially arranged. The incident light of the vibration target sequentially passes through the primary mirror and the secondary mirror, is transmitted into the beam splitting cube mirror, becomes two beams with the same beam through the beam splitter, and finally is imaged on the camera photosensitive planes of the area array vision system and the linear array vision system through the imaging lens group lens. The area array visual system and the linear array visual system are connected with a computer through cables, so that real-time transmission and rapid analysis processing are realized.
The lens combination of the imaging spherical main mirror and the imaging spherical secondary mirror is used for converging and imaging diffuse reflection light of a vibration target, the incident light is focused and imaged for the first time through the main mirror, and the imaging is carried out at the object focal plane of the secondary mirror, and nearly parallel light beams are formed through the secondary mirror, so that far object light is focused and collimated to enter the beam splitting prism;
the beam splitting prism has a system beam splitting function, and equally divides incident light into two beams which respectively enter the area array vision system and the linear array vision system;
the area array vision system is a group of area array lenses and an area array camera, and converts low-frequency vibration optical signals of a measurement target into electric signals through a photosensitive element which is collected at a low speed;
the linear array vision system is a group of linear array lenses and linear array cameras, and the medium-high frequency vibration optical signals of the measurement target are converted into electric signals through the photosensitive elements which are collected at high speed.
The cable connects the linear array vision system and the area array vision system with the computer, and transmits data transmission signals and acquisition control signals.
The computer is used as a control center and comprises an image acquisition card and an acquisition storage device, and the related computer measurement program can be operated to modify related acquisition parameters, control acquisition instructions and store vibration image data, so that the functions of preprocessing the vibration image and measuring and analyzing target vibration response are realized.
The invention discloses a line-surface camera combination-based spectroscopic imaging visual vibration measurement method, which is realized based on a line-surface camera combination spectroscopic imaging visual vibration measurement system and comprises the following steps:
s1: and installing the target piece for vibration measurement on a vibration test platform, and adjusting the optical imaging module to enable imaging of the static measurement target on a computer to be clear.
The vibration test platform is a one-dimensional vibration table or a two-dimensional plane vibration table, and the vibration measurement target is fixed on the vibration test platform. The optical imaging adjusting module comprises position adjustment of an imaging main mirror and a secondary mirror, focal length adjustment of a linear array lens and an area array lens and aperture adjustment of a light source and a camera.
S2: the optical imaging module is kept fixed, the linear array camera and the area array camera are calibrated, internal parameters and external parameters of the camera are obtained, and an imaging model and a lens distortion model of the area array system are respectively built.
The calibration process is to adopt a luminous plane coding target to carry out a calibration test, obtain image data after passing through a spherical mirror, a prism and a camera imaging lens, and take luminous characteristic points as calibration points.
The calibration is based on ideal pinhole imaging of a camera, and a target world coordinate system O-X is established w Y w Z w Conversion relation to a pixel coordinate system uv, namely an imaging geometric model I of an area array system and an imaging geometric model II of a linear array system:
wherein (X) w ,Y w ,Z w ,1) T Is the homogeneous coordinate of a certain characteristic point in the calibration target in a world coordinate system, Z cI And Z cII Is a proportionality constant (u) I ,v I ) The main point position of the imaging plane of the area array camera, u 0II Is the principal point of the imaging plane of the linear array camera. f (f) I And f II Lens focal lengths d of the area array system and the linear array system respectively xI And d yI Is the physical size of a single pixel of the area array camera, d xII And d yII Is the physical size of a single pixel of a line camera. Internal parameters of the area array camera are defined byu 0I 、v 0I Determining; the linear array camera is equivalent to a special area array camera, and the internal reference of the linear array camera is +.>u 0II And (5) determining. R is R I 、T I And R is II 、T II The rotation matrix and the translation matrix respectively from the world coordinate system to the area array camera coordinate system and the linear array camera coordinate system belong to external parameters of a camera system.
Obtaining an internal reference matrix and an external reference matrix of the area array system and the linear array system through the calibration; meanwhile, nonlinear distortion of radial, centrifugal and thin prisms existing due to design, manufacture and assembly of the lens can be corrected through calibration, and accuracy is improved.
S3: after calibration, setting sampling parameters of an area array system and a linear array system by a computer, acquiring the area array vision system at a low sampling frequency, acquiring the linear array vision system at a high frequency, triggering by computer upper computer software, synchronously acquiring two paths of system video images, and storing target vibration video data.
S4: and the computer processes the stored video or image sequence offline to perform edge extraction and target positioning, so that the subpixel measurement accuracy of the system is improved.
4.1, adopting a subpixel-level high-precision Canny edge detection algorithm to a two-dimensional image sequence acquired by the face-area camera, and carrying out edge positioning on a moving target with low frequency and wide vibration range of the face-area camera, namely smoothing image denoising through Gaussian filtering, searching image gradients, carrying out non-maximum suppression of the gradients, determining potential edges by using a double-threshold method, and tracking boundaries by using a hysteresis technology.
4.2, adopting a linear fitting method based on a gradient operator to an image sequence acquired by the linear camera to realize the extraction of the edge of the vibration target, and positioning the target and tracking the motion along with the time sequence.
4.2.1, determining a fitting window with good linearity in a local edge transition zone;
and intercepting a part with better linearity in the middle of the edge transition zone as a fitting window. For a one-dimensional image vector, the gray value of pixel x is expressed as y x . First, the gray threshold y of the signal of the whole edge transition zone is determined L And y H Then transition formula y according to gray value l ＝y L +0.25(y H -y L ) And y h ＝y L +0.75(y H -y L ) Determining two edges y of the fitting window l And y h And their corresponding pixel locations.
4.2.2, finding out a rough edge position in a fitting interval by utilizing a gradient operator;
fitting window [ l, h ] determined at 4.2.1]Within the interval, a one-dimensional gradient formula R is adopted x ＝|y x+1 -y x Computing gradient magnitude, where x ε [ l, h-1]Finding out the pixel interval (x 0 ,x 0 +1), x 0 As the center of the image edge coarse positioning.
4.2.3, symmetrically selecting adjacent pixel points of the coarse positioning center as a fitting object in a fitting window, and fitting linear coordinates of edges;
at the gradient maximum point x 0 In the field of the center, 2n points are symmetrically selected, and n is an integer. And (3) carrying out gray value straight line fitting on the 2n+1 points by adopting a least square method, wherein the fitting straight line is y=bx+a. According to the principle of the least square method, the parameter slope of the straight fitting line which minimizes the square sum of errors is obtainedAnd intercept->
4.2.4 two points x at gradient maximum 0 And x 0 Taking the average value of the +1 gray values as a threshold value to intercept image sub-pixel edge points;
will x 0 And x 0 +1 is substituted into the fitting linear equation to obtain a fitting gray scale estimated value, and the average value of two gray scales is used Coordinate point +.>As sub-pixel edge coordinates. And the whole pixel edge extracted from the original one-dimensional edge is improved to the sub-pixel edge coordinate obtained by fitting a straight line, so that the measurement accuracy of the sub-pixels of the system is improved.
S5: and calculating the actual space time-course displacement of the vibration target through the imaging edge coordinate points of the vibration target in the two systems respectively.
And (3) extracting the coordinates of the feature points of the vibration edge of each frame of picture, converting the coordinates of the feature points into actual coordinates of a world coordinate system according to the calibration parameters in S2, obtaining two time-course displacement curves of each feature point along with each frame of picture, and performing time alignment on the two feature curves.
S6: and performing fast Fourier transform on the vibration time-course displacement sequences of the same pair of image feature point coordinates, converting the time domain signals into the frequency domain to obtain signal amplitude spectrums, calculating power spectrum estimation on each frequency component, and fusing and analyzing the frequency values and the amplitudes of vibration and related resonance to enlarge the frequency range of visual vibration measurement.
The vibration frequency characteristic analysis capability of the image characteristic is related to the image sampling frequency of the vision system, and the frequency measurement range of the area array vision system is far smaller than that of the linear array vision system because the sampling frequency of the area array system is far lower than that of the linear array system. The two systems are transformed, the vibration scale is uniform in a world coordinate system, and when the vibration characteristics are fused, the frequency measurement results of the two frequency systems are fused by using an average weighting method, so that the system can obtain the vibration frequency characteristics up to the frequency range of kHz, and the frequency range of visual vibration measurement is enlarged.
The beneficial effects are that:
1. the invention discloses a spectroscopic imaging visual vibration measurement system and a spectroscopic imaging visual vibration measurement method based on combination of a line-plane camera, which are used for synchronously controlling a line-array camera to acquire a high-frequency vibration image and a plane-array camera to acquire a low-frequency vibration image, so that the vibration frequency measurement range of a single visual system is widened;
2. the spectral imaging visual vibration measurement system and the spectral imaging visual vibration measurement method based on the combination of the line-plane cameras can provide rough position basis for positioning targets and measuring targets of the line-array cameras by means of the large visual field range of the line-array cameras during calibration and measurement, and reduce the operation difficulty of a line-array visual system;
3. according to the spectral imaging visual vibration measurement system and method based on the combination of the line-plane camera, a high-precision Canny edge detection algorithm and a linear fitting method based on a gradient operator are selected for different vibration conditions, and for a two-dimensional image with low-frequency and large-amplitude vibration, the Canny algorithm can identify actual edges in the image as much as possible, and the identified edges are very close to the actual edges in the actual image; the Canny algorithm based on the two-dimensional image is not suitable for the linear array one-dimensional image, for the high-frequency small-amplitude vibration one-dimensional image, a linear fitting method based on a gradient operator is adopted, accurate fitting is performed after coarse positioning, sub-pixel edge accurate positioning in an edge transition section of the one-dimensional image is achieved, and detection accuracy of a linear array system is improved.
Drawings
FIG. 1 is a block diagram of a spectral imaging visual vibration measurement system based on line-to-plane camera integration as disclosed in the present invention;
FIG. 2 is a flow chart of a method for measuring spectral imaging visual vibration based on line-to-surface camera combination in accordance with the present disclosure;
FIG. 3 is a schematic diagram of a simulation structure of an imaging system and a simulation of geometric imaging in the system and method for measuring spectral imaging visual vibration based on line-plane camera combination disclosed in the present embodiment;
wherein (a) the diagram is the structure and simulation result of a simple lens telescopic imaging system; (b) The diagram is the structure and simulation result of the telescopic imaging system after the lens combination is optimized;
fig. 4 is an example of a spectroscopic imaging visual vibration measurement system based on line-to-plane camera combination disclosed in this embodiment.
Detailed Description
In order that the invention may be more clearly understood, a more particular description thereof will be rendered by reference to specific embodiments that are illustrated in the appended drawings. The technical problems and the beneficial effects solved by the technical proposal of the invention are also described, and the described embodiment is only used for facilitating the understanding of the invention and does not have any limiting effect.
The invention discloses a spectral imaging visual vibration measurement system based on combination of a line-plane camera, which comprises an imaging spherical primary mirror, an imaging spherical secondary mirror, a spectral prism, an area array visual system, a line array visual system, a data cable and a computer. The incident light of the vibration target sequentially passes through the primary mirror and the secondary mirror, is transmitted into the beam splitting cube mirror, becomes two beams with the same beam through the beam splitter, and finally is imaged on the camera photosensitive planes of the area array vision system and the linear array vision system through the imaging lens group lens. The imaging spherical primary mirror, the imaging spherical secondary mirror and the beam splitting prism are coaxially arranged in sequence; the linear array vision system and the area array vision system are respectively arranged on two sides of emergent light of the beam splitting prism, optical axes are mutually perpendicular, the linear array vision system and the beam splitting prism transmit the emergent light and are coaxially arranged, and the optical axes of the area array vision system and the beam splitting prism reflect the emergent light and are coaxially arranged. The area array visual system and the linear array visual system are connected with a computer through cables, so that real-time transmission and rapid analysis processing are realized.
The lens combination of the imaging spherical main mirror and the imaging spherical secondary mirror is used for converging and imaging diffuse reflection light rays of a vibration target, incident light rays are focused and imaged for the first time through the main mirror, and near parallel light beams are formed through the secondary mirror at the object focal plane of the secondary mirror, so that far object light rays are focused and collimated to enter the beam splitting prism, the distance between the main mirror and the secondary mirror in the focusing process is adjusted along with the change of the imaging distance, and the far object light rays are focused and collimated, so that the light beams entering the beam splitting prism are more converged. The primary mirror and the secondary mirror form a kepler telescope type afocal system, and if the focal length of the primary mirror is f 1 The focal length of the secondary mirror is f 2 The telescope optical system of the primary mirror and the secondary mirror has the visual magnification of
In the embodiment, a non-polarized beam splitter prism with the ratio of 1:1 is selected, and non-polarized incident light is split into a reflected light beam and a transmitted light beam with the same light intensity by the prism, and the reflected light beam and the transmitted light beam are captured by a linear array camera lens and an area array camera lens respectively. In the beam splitting process, no beam displacement, transmission and reflection optical path lengths are equal.
The area array vision system is a group of area array lenses and an area array camera, the low-frequency vibration optical signals of the measuring target are converted into electric signals through the photosensitive elements collected at low speed, the linear array vision system is a group of linear array lenses and a group of linear array camera, and the medium-high-frequency vibration optical signals of the measuring target are converted into electric signals through the photosensitive elements collected at high speed. The installation of the optical imaging module requires that the primary mirror, the secondary mirror and the beam splitter prism are coaxial, the optical axis of the lens of the linear array camera is coincident with the emergent optical axis of the beam splitter prism, the optical axis of the lens of the same area array camera is consistent with the emergent optical axis of the beam splitter prism, and the installation error is reduced as much as possible. The design of the linear array camera and the lens thereof needs to comprehensively consider the factors such as the resolution of the linear array-area array camera, the coordinated depth of field and the angle of view of the two systems, and meanwhile, the structural optimization of the optical imaging spherical lens needs to be further carried out because the linear array system is greatly influenced by distortion.
The result of the structure simulation and the geometric structure simulation of the optical imaging system is shown in fig. 3 (a), the imaging distortion of the single lens is larger, the single lens is formed by simulating and optimizing the primary lens and the secondary lens, the single lens is replaced by the double-cemented lens combination, the result of the structure simulation and the geometric structure simulation of the optical imaging system is shown in fig. 3 (b), the imaging phase difference and the distortion are reduced, and the imaging quality is enhanced.
The system shown in the embodiments is applied to a vibration measurement range of l=100×100mm, and according to the principle of aperture imaging, at a working distance d=1m, the working level viewing angleThe area array system expects that the optical system precision reaches 0.1mm/pixel, so the area array camera has 1280 multiplied by 1024 resolution, and the sea-Kangwei vision MV-CA013-21UM with the pixel size of 4.8UM can meet the requirement. The main parameters of the lens are the parameters of focal length, aperture, interface and the like, and the imaging comprehensive focal length of the area-array camera is +.>Therefore, the M5028-MPW2 with the focal length of 50mm, the aperture of F2.8-16.0, the C interface and the field of view of 7.5 degrees multiplied by 10.0 degrees is selected for the area array camera, and the system requirement can be met.
According to depth of field formulaWhere F is the focal length of the lens, F is the photographing aperture value of the lens, L is the focusing distance, δ is the diameter of the circle of confusion, and typically 0.03mm is taken. In practice, in order to ensure enough brightness after light splitting, the aperture is set to be the maximum aperture of 2.8, the focusing distance is about 1000mm, the focal length is 50mm, and the focal length is substituted into a depth of field calculation formula to calculate to obtain an area array phaseThe depth of field DeltaL of the camera is approximately 10.37m.
The linear array camera generally has higher resolution, and the optical precision close to 4 times can be obtained by selecting a type L5047MG140 linear array camera with 4096×2 resolution, 28kHz frame rate and 7um pixel size.
In order to enable the imaging depth of field of the system to be matched with that of the area array camera system, the same depth of field, aperture and focusing distance are substituted into the linear array camera to calculate the focal length of a lens of the linear array camera to be about 93.49mm, a lens SV-10035V (aperture F2.8-close, C interface, field of view 2.9 degrees multiplied by 3.8 degrees, target surface 1/2 and working distance greater than 1000 mm) of the 100mm focal length camera is selected.
The cable connects the optical imaging module with the computer, and transmits data transmission signals and acquisition control signals.
The computer is used as a system control center and comprises an image acquisition card and an acquisition storage device, and related acquisition parameters can be modified, acquisition instructions can be controlled and vibration image data can be stored by running related computer measurement programs, so that the functions of vibration image preprocessing and target vibration response measurement analysis are further realized.
The invention discloses a line-surface camera combination-based spectroscopic imaging visual vibration measurement method, which is realized based on the line-surface camera combination spectroscopic imaging visual vibration measurement system, as shown in fig. 2, and comprises the following steps:
s1: and installing a vibration target and debugging the system. Firstly, a target piece to be subjected to vibration measurement is installed on a test platform, and a system is debugged, wherein the adjustment of a light source, the position adjustment of a primary mirror and a secondary mirror, the imaging focusing of a linear lens and an area lens and the like are included. After focusing debugging is completed, the positions of all parts of the system are unchanged, and an image matching model of the linear array and the area array image is unchanged. The imaging target of the linear array system is captured, the spatial position of the target point can be adjusted to be within the visual field range of the linear array camera by means of the large frame of the area array camera, and the linear array camera is controlled to effectively acquire the motion trail of the high-frequency moving object. And adjusting the spatial position of the target point to be within the visual field range of the linear array camera by means of the large frame displayed by the area array system, and controlling the linear array camera to effectively acquire the motion trail of the high-frequency moving object.
S2: the optical imaging module is kept fixed, the linear array camera and the area array camera are calibrated, internal parameters and external parameters of the camera are obtained, and an imaging model and a lens distortion model of the area array system are respectively built.
The calibration process is to adopt a luminous plane coding target to carry out a calibration test, obtain image data after passing through a spherical mirror, a prism and a camera imaging lens, and take luminous characteristic points as calibration points.
The calibration is to establish a target world coordinate system O-X based on ideal aperture imaging of a camera w Y w Z w Conversion relation to the pixel coordinate system uv. For an area array camera, a more mature Zhang Zhengyou calibration method is adopted. And calibrating the linear array camera by adopting a static imaging method for controlling the translational movement of the 2D plane luminous target. The large visual field range of the area array camera can also provide rough position basis for positioning targets and measuring targets of the linear array camera, and the operation and use difficulty of the linear array vision system calibration is reduced.
Calibration establishes world coordinates (X w ,Y w ,Z w ) The transformation relation between the two pixel coordinates (u, v) is that the imaging geometric model I of the area array system and the imaging geometric model II of the linear array system are as follows:
wherein (X) w ,Y w ,Z w ,1) T Is the homogeneous coordinate of a certain characteristic point in the calibration target in a world coordinate system, Z cI And Z cII Is a proportionality constant (u) I ,v I ) The main point position of the imaging plane of the area array camera, u 0II Is the principal point of the imaging plane of the linear array camera. f (f) I And f II Lens focal lengths d of the area array system and the linear array system respectively xI And d yI Is the physical size of a single pixel of the area array camera, d xII And d yII Is the physical size of a single pixel of a line camera. Obtaining internal parameters by an area array camerau 0I 、v 0I Determining; the linear array camera is equivalent to a special area array camera, and the internal reference of the linear array camera is +.>u 0II And (5) determining. R is R I 、T I And R is II 、T II The rotation matrix and the translation matrix respectively from the world coordinate system to the area array camera coordinate system and the linear array camera coordinate system belong to external parameters of a camera system.
The internal reference matrix and the external reference matrix of the two systems are obtained through calibration, meanwhile, due to the design, manufacturing and assembly problems of the lens, the lens has nonlinear distortion of three aspects of radial, centrifugal and thin prism, and the lens distortion can be corrected through calibration so as to improve the precision.
S3: after calibration, setting sampling parameters of an area array system and a linear array system through a vibration measurement analysis module, acquiring the area array vision system at a low sampling frequency smaller than hundred hertz, acquiring the linear array vision system at a high frequency of about 10kHz, triggering by computer upper computer software, synchronously acquiring two paths of system video images, and storing target vibration video data.
S4: and (5) processing the stored video or image sequence offline through a vibration measurement analysis module, and carrying out edge extraction and target positioning. The two-dimensional image sequence acquired by the array camera adopts a subpixel-level high-precision Canny edge detection algorithm, and the image sequence acquired by the array camera adopts a linear fitting method based on a gradient operator to realize the edge extraction of a vibration target, and positions the target and tracks the motion along with a time sequence.
And 4.1, carrying out gray preprocessing on a two-dimensional image sequence acquired by the area array camera, and adopting a subpixel-level high-precision Canny edge detection algorithm.
4.1.1, smoothing the traversed picture by adopting a Gaussian filter as a convolution kernel, wherein the edge of the image is easily interfered by noise, and the Gaussian smoothing treatment effectively filters out high-frequency noise superposed in an ideal image.
And 4.1.2, calculating the amplitude and the direction of the gradient by using a Sobel operator, traversing pixel points one by one, judging that the current pixel point is the maximum value with the same gradient direction in surrounding pixel points, and inhibiting non-edge points to obtain the strong edge of the image.
4.1.3, converting the image into a binarized image, screening the binarized image by using a double threshold, and obtaining an edge image closest to the real edge of the image by selecting a proper large threshold and a proper small threshold, thereby obtaining the image edge information of the sub-pixels with high precision.
And 4.1.4, extracting the coordinates of the edge feature points of the vibration target of each frame of picture, and calculating the change difference value of the coordinates of the feature points of each frame by taking the coordinates of the first frame as a reference.
4.2, when the target vibration frequency is high and the vibration amplitude is very small, the acquisition rate of the area array camera cannot meet the vibration characteristic measurement requirement, and the Canny algorithm based on the two-dimensional image is not suitable for linear array to process one-dimensional images. Because of the aberrations and diffraction, the actual one-dimensional image edge is a gradually changing transition signal, and therefore edge feature points need to be accurately fitted or interpolated in the transition signal. The system provides a gradient operator-based linear fitting method, wherein the gradient operator-based linear fitting method is that firstly, a rough edge position is found out by utilizing a gradient operator, then, adjacent pixel points are symmetrically selected in the fitting field to serve as fitting objects by taking the rough position as a center, and the method is more accurate for linear fitting of edge position compared with least square.
4.2.1, determining a fitting window with good linearity in a local edge transition zone;
and intercepting a part with better linearity in the middle of the edge transition zone as a fitting window. For one-dimensional image vector, let the gray value of pixel x be expressed as y x The gray threshold y of the signal of the whole edge transition zone is firstly determined L And y H According to the gray value transition formula y l ＝y L +0.25(y H -y L ) And y h ＝y L +0.75(y H -y L ) Determining two edges y of the fitting window l And y h And their corresponding pixel locations.
4.2.2, finding out a rough edge position in a fitting interval by utilizing a gradient operator;
fitting window [ l, h ] determined at 4.2.1]Within the interval, a one-dimensional gradient formula R is adopted x ＝|y x+1 -y x Computing gradient magnitude, where x ε [ l, h-1]Find out the pixel interval (x 0 ,x 0 +1), x 0 As the center of the image edge coarse positioning.
4.2.3, symmetrically selecting adjacent pixel points of the coarse positioning center in a fitting window as fitting objects, and fitting edge linear coordinates;
with gradient maximum point x 0 2n points (n is an integer, usually 2,3,4 and …) are symmetrically selected in the central field, and gray value straight line fitting is performed on the 2n+1 points by adopting a least square method. Let the fitting line be y=bx+a, calculate the slope of the fitting line parameter according to the least square methodAnd intercept->So that the sum of squares error-> Minimum.
Will e 2 Partial derivatives are obtained on a and b, and the reciprocal is respectively zero:
solving the derivative equation set to obtain the parameter slopeAnd intercept->
4.2.4, finally at two points x of gradient maximum 0 And x 0 Taking the average value of the +1 gray values as a threshold value to intercept image sub-pixel edge points;
will x 0 And x 0 +1 is substituted into the fitting linear equation to obtain a fitting gray scale estimated value, and the average value of two gray scales is used Coordinate point +.>As sub-pixel edge coordinates. According to the method, the whole pixel edge extracted from the original one-dimensional edge is improved to the sub-pixel edge coordinate obtained by fitting a straight line, so that the sub-pixel measurement accuracy of the system is improved.
S5: and calculating the actual space time-course displacement of the vibration target through the imaging edge coordinate points of the vibration target in the two systems respectively.
And (3) extracting the coordinates of the feature points of the vibration edge of each frame of picture, converting the coordinates of the feature points into actual coordinates of a world coordinate system according to the calibration parameters in S2, obtaining two time-course displacement curves of each feature point along with each frame of picture, and performing time alignment on the two feature curves.
S6: performing fast Fourier transform on the vibration time-course displacement sequences of the same pair of image feature point coordinates, converting time domain signals into frequency domains to obtain signal amplitude spectrums, calculating power spectrum estimation on each frequency component, and fusion analyzing frequency values and amplitudes of vibration and related resonance.
The vibration frequency characteristic analysis capability of the image characteristic is related to the image sampling frequency of the vision system, and the frequency measurement range of the area array vision system is far smaller than that of the linear array vision system because the sampling frequency of the area array system is far lower than that of the linear array system. The two systems are transformed, the vibration scale is uniform in a world coordinate system, and when the vibration characteristics are fused, the frequency measurement results of the two frequency systems are fused by using an average weighting method, so that the system can obtain the vibration frequency characteristics up to the frequency range of kHz, and the frequency range of visual vibration measurement is enlarged.
The foregoing detailed description has set forth the objects, aspects and advantages of the invention in further detail, it should be understood that the foregoing description is only illustrative of the invention and is not intended to limit the scope of the invention, but is to be accorded the full scope of the invention as defined by the appended claims.
Claims (8)
1. Spectral imaging visual vibration measurement system based on line-face camera combines, its characterized in that: the system comprises an imaging spherical primary mirror, an imaging spherical secondary mirror, a beam splitting prism, an area array vision system, a linear array vision system, a data cable and a computer; the imaging spherical primary mirror, the imaging spherical secondary mirror and the beam splitting prism are coaxially arranged in sequence; the linear array visual system and the area array visual system are respectively arranged on two sides of emergent light of the beam splitting prism, optical axes are mutually perpendicular, the linear array visual system and the beam splitting prism transmit the emergent light and are coaxially arranged, and the optical axes of the area array visual system and the beam splitting prism reflect the emergent light and are coaxially arranged; incident light of the vibration target sequentially passes through the primary mirror and the secondary mirror, is transmitted into the beam splitting cube mirror, becomes two beams with the same beam through the beam splitter, and finally is imaged on the camera photosensitive planes of the area array vision system and the linear array vision system through the imaging lens group lens; the area array visual system and the linear array visual system are connected with a computer through cables, so that real-time transmission and rapid analysis processing are realized.
2. The line-to-surface camera combination based spectroscopic imaging visual vibration measurement system of claim 1 wherein: the lens combination of the imaging spherical main mirror and the imaging spherical secondary mirror is used for converging and imaging diffuse reflection light of a vibration target, the incident light is focused and imaged for the first time through the main mirror, and the imaging is carried out at the object focal plane of the secondary mirror, and nearly parallel light beams are formed through the secondary mirror, so that far object light is focused and collimated to enter the beam splitting prism;
the beam splitting prism has a system beam splitting function, and equally divides incident light into two beams which respectively enter the area array vision system and the linear array vision system;
the area array vision system is a group of area array lenses and an area array camera, and converts low-frequency vibration optical signals of a measurement target into electric signals through a photosensitive element which is collected at a low speed;
the linear array vision system is a group of linear array lenses and linear array cameras, and medium-high frequency vibration optical signals of a measurement target are converted into electric signals through a photosensitive element which is collected at a high speed;
the cable connects the linear array visual system and the area array visual system with the computer, and transmits data transmission signals and acquisition control signals;
the computer is used as a control center and comprises an image acquisition card and an acquisition storage device, and the related computer measurement program can be operated to modify related acquisition parameters, control acquisition instructions and store vibration image data, so that the functions of preprocessing the vibration image and measuring and analyzing target vibration response are realized.
3. The line-plane camera combined spectroscopic imaging visual vibration measurement method is realized based on the line-plane camera combined spectroscopic imaging visual vibration measurement system, and is characterized in that: comprises the following steps of the method,
s1: the method comprises the steps of installing a vibration measurement target on a vibration test platform, and adjusting an optical imaging module to enable imaging of a static measurement target on a computer to be clear;
s2: the optical imaging module is kept fixed, the linear array camera and the area array camera are calibrated, internal parameters and external parameters of the camera are obtained, and an imaging model and a lens distortion model of the area array system are respectively built;
s3: after calibration, setting sampling parameters of an area array system and a linear array system by a computer, acquiring the area array vision system at a low sampling frequency, acquiring the linear array vision system at a high frequency, triggering by computer upper computer software, synchronously acquiring two paths of system video images, and storing target vibration video data;
s4: the stored video or image sequence is processed offline through a computer, edge extraction and target positioning are carried out, and the sub-pixel measurement accuracy of the system is improved;
s5: calculating actual space time-course displacement of the vibration target through the imaging edge coordinate points of the vibration target in the two systems respectively;
s6: and performing fast Fourier transform on the vibration time-course displacement sequences of the same pair of image feature point coordinates, converting the time domain signals into the frequency domain to obtain signal amplitude spectrums, calculating power spectrum estimation on each frequency component, and fusing and analyzing the frequency values and the amplitudes of vibration and related resonance to enlarge the frequency range of visual vibration measurement.
4. A line-to-surface camera combination based spectroscopic imaging visual vibration measurement method as defined in claim 3 wherein: the implementation method of the S1 is that,
the vibration test platform is a one-dimensional vibration table or a two-dimensional plane vibration table, and a vibration measurement target is fixed on the vibration test platform; the optical imaging adjusting module comprises position adjustment of an imaging main mirror and a secondary mirror, focal length adjustment of a linear array lens and an area array lens and aperture adjustment of a light source and a camera.
5. The line-to-surface camera combination based spectroscopic imaging visual vibration measurement method of claim 4 wherein: the implementation method of the S2 is that,
the calibration process is to adopt a luminous plane coding target to carry out a calibration test, obtain image data after passing through a spherical mirror, a prism and a camera imaging lens, and take luminous characteristic points as calibration points;
the calibration is based on camera idealityIs used for imaging small holes and establishing a target world coordinate system O-X w Y w Z w Conversion relation to a pixel coordinate system uv, namely an imaging geometric model I of an area array system and an imaging geometric model II of a linear array system:
wherein (X) w ,Y w ,Z w ,1) T Is the homogeneous coordinate of a certain characteristic point in the calibration target in a world coordinate system, Z cI And Z cII Is a proportionality constant (u) I ,v I ) The main point position of the imaging plane of the area array camera, u 0II Is the main point of the imaging plane of the linear array camera; f (f) II And f III Lens focal lengths d of the area array system and the linear array system respectively xI And d yI Is the physical size of a single pixel of the area array camera, d xII And d yII Is the physical size of a single pixel of the linear array camera; internal parameters of the area array camera are defined byu 0I 、v 0I Determining; the linear array camera is equivalent to a special area array camera, and the internal reference of the linear array camera is +.>u 0II Determining; r is R I 、T I And R is II 、T II The rotation matrix and the translation matrix respectively from the world coordinate system to the area array camera coordinate system and the linear array camera coordinate system belong to external parameters of a camera system;
obtaining an internal reference matrix and an external reference matrix of the area array system and the linear array system through the calibration; meanwhile, nonlinear distortion of radial, centrifugal and thin prisms existing due to design, manufacture and assembly of the lens can be corrected through calibration, and accuracy is improved.
6. The line-to-surface camera combination based spectroscopic imaging visual vibration measurement method of claim 5 wherein: the implementation method of the S4 is that,
4.1, adopting a subpixel-level high-precision Canny edge detection algorithm to a two-dimensional image sequence acquired by the face-area camera, and carrying out edge positioning on a moving target with low frequency and wide vibration range of the face-area camera, namely smoothing image denoising through Gaussian filtering, searching image gradients, carrying out non-maximum suppression of the gradients, determining potential edges by using a double-threshold method, and tracking boundaries by using a hysteresis technology;
4.2, adopting a linear fitting method based on a gradient operator to an image sequence acquired by the linear camera to extract the edge of the vibration target, and positioning the target and tracking the motion along with the time sequence;
4.2.1, determining a fitting window with good linearity in a local edge transition zone;
intercepting a part with better middle linearity of an edge transition zone as a fitting window; for a one-dimensional image vector, the gray value of pixel x is expressed as y x The method comprises the steps of carrying out a first treatment on the surface of the First, the gray threshold y of the signal of the whole edge transition zone is determined L And y H Then transition formula y according to gray value l ＝y L +0.25(y H -y L ) And y h ＝y L +0.75(y H -y L ) Determining two edges y of the fitting window l And y h And its corresponding pixel location;
4.2.2, finding out a rough edge position in a fitting interval by utilizing a gradient operator;
fitting window [ l, h ] determined at 4.2.1]Within the interval, a one-dimensional gradient formula R is adopted x ＝|y x+1 -y x Computing gradient magnitude, where x ε [ l, h-1]Finding out the pixel interval (x 0 ,x 0 +1), x 0 As an image edge rough positioning center;
4.2.3, symmetrically selecting adjacent pixel points of the coarse positioning center as a fitting object in a fitting window, and fitting linear coordinates of edges;
at the gradient maximum point x 0 In the field of the center, 2n points are symmetrically selected, and n is an integer; carrying out gray value straight line fitting on the 2n+1 points by adopting a least square method, wherein the fitted straight line is y=bx+a; according to the principle of the least square method, the parameter slope of the straight fitting line which minimizes the square sum of errors is obtainedAnd intercept->
4.2.4 two points x at gradient maximum 0 And x 0 Taking the average value of the +1 gray values as a threshold value to intercept image sub-pixel edge points;
will x 0 And x 0 +1 is substituted into the fitting linear equation to obtain a fitting gray scale estimated value, and the average value of two gray scales is used Coordinate point +.>As sub-pixel edge coordinates; and the whole pixel edge extracted from the original one-dimensional edge is improved to the sub-pixel edge coordinate obtained by fitting a straight line, so that the measurement accuracy of the sub-pixels of the system is improved.
7. The line-to-surface camera combination based spectroscopic imaging visual vibration measurement method of claim 6, wherein: the implementation method of the S5 is that,
and (3) extracting the coordinates of the feature points of the vibration edge of each frame of picture, converting the coordinates of the feature points into actual coordinates of a world coordinate system according to the calibration parameters in S2, obtaining two time-course displacement curves of each feature point along with each frame of picture, and performing time alignment on the two feature curves.
8. The line-to-surface camera combination based spectroscopic imaging visual vibration measurement method of claim 7, wherein: the implementation method of the S6 is that,
the vibration frequency characteristic analysis capability of the image characteristic is related to the image sampling frequency of the visual system, and the frequency measurement range of the area array visual system is far smaller than that of the linear array visual system because the sampling frequency of the area array system is far lower than that of the linear array system; the two systems are transformed, the vibration scale is uniform in a world coordinate system, and when the vibration characteristics are fused, the frequency measurement results of the two frequency systems are fused by using an average weighting method, so that the system can obtain the vibration frequency characteristics up to the frequency range of kHz, and the frequency range of visual vibration measurement is enlarged.
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