CN115962839A - Spatial linear vibration measurement method based on machine vision - Google Patents
Spatial linear vibration measurement method based on machine vision Download PDFInfo
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- CN115962839A CN115962839A CN202211237065.9A CN202211237065A CN115962839A CN 115962839 A CN115962839 A CN 115962839A CN 202211237065 A CN202211237065 A CN 202211237065A CN 115962839 A CN115962839 A CN 115962839A
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Abstract
The invention discloses a space linear vibration measuring method based on machine vision, which comprises the following steps of fixing a laser capable of generating two mutually perpendicular laser beams at the central position of a platform of a space linear vibration generating device, and ensuring that two laser beams generated by the laser form two circular light spots on a laser receiving panel in front of the vibration generating device; calibrating a camera by using a machine vision method, quickly positioning the areas where the two light spots are located aiming at the image characteristics on the laser receiving panel, and separating effective light spot information points and background noise information points in the light spot areas by using a reliable threshold segmentation algorithm; the light spot center position is obtained by fitting and resolving the light spot information points of each frame of image, so that the space linear vibration information generated by the space linear vibration generating device is obtained. According to the method, the measurement of the space linear vibration information can be completed only by matching one camera with one laser and one laser receiving panel, and the method has the advantages of high efficiency, simplicity and convenience and the like.
Description
Technical Field
The invention belongs to the field of vibration testing, and particularly relates to a space linear vibration measuring method based on machine vision.
Background
Vibration is a common phenomenon in the nature, and the vibration conditions of facilities and equipment need to be monitored in important fields such as buildings, aerospace and the like, so that the damage condition of the equipment structure caused by vibration fatigue is prevented. The spatial vibration condition can be expressed in a spatial coordinate system as linear vibration in three mutually perpendicular directions, the traditional vibration monitoring method usually utilizes a triaxial vibration sensor to carry out spatial vibration monitoring, however, due to the aging of internal sensitive elements of the sensor, the sensor needs to be periodically calibrated to ensure the validity of a measuring result, but the periodic calibration work of the sensor after the arrangement is difficult to carry out, so that the accuracy of the sensor in long-term work cannot be ensured; spatial vibrations can also be measured using optical devices such as laser vibrometers, but laser devices have high environmental requirements, can only be measured in laboratories, and are costly.
Disclosure of Invention
Aiming at the defects of inaccurate measurement, fixed monitoring position and the like of the traditional vibration monitoring method, the invention provides a simple, convenient, flexible and low-cost spatial vibration measuring method based on machine vision, which can greatly reduce the arrangement quantity of sensors for traditional vibration monitoring and measure spatial vibration information at any position, and specifically comprises the following steps:
firstly, fixing a laser at the central position of a platform of a spatial linear vibration generating device, and ensuring that two beams of mutually vertical lasers generated by the laser form two circular light spots on a laser receiving panel in front of the vibration generating device; calibrating a camera by using a machine vision method to obtain an H matrix of the plane conversion relation between the camera and the laser receiving panel,
wherein the parameter h 11 ,h 12 ,h 13 ,h 21 ,h 22 ,h 23 ,h 31 ,h 32 ,h 33 Common watchThe internal reference and the external reference of the camera are achieved.
Sequence image F of j frame laser motion collected by camera j (x, y), performing convolution operation on each frame of image and the mean value filtering convolution kernel g (x, y) to obtain processed j frames of light spot moving images M j (x,y)，
At M j Searching the maximum gray level of each frame of image in (x, y), rapidly positioning the region where the light spot of each frame is located, determining the region of interest R of each frame of image, and performing light spot sub-region R on the region of interest R by using the optimal threshold k obtained by the maximum inter-class variance 1 And a background subregion R 2 And (4) dividing.
Wherein p is 1 M is the probability that the gray scale of a certain pixel in the R region is less than the gray scale threshold k G Is the mean value of the grays of the R region, m is the mean value of the grays with the gray level k,
wherein, mu i The probability of the gray level of the pixel point being i is shown.
For light spot R 1 Set of pixel gray levels in region { R 1 (x, y) } obtaining the center of the light spot by Gaussian fitting,
wherein A is the gray peak value of the light spot, and the fitted central coordinate of the light spot is (x) center ,y center ),
Is x-axis standard deviation,. Sup.>
Is the standard deviation of the y-axis.
For each frame image M j (x j ,y j ) R of (A) to (B) 1 Two spot centers (x) of the laser are obtained by the formula (5) in the region jL1, y jL1 )、(x jL2, y jL2 ) The spatial vibration information (d) of the j-th frame of the vibration generating device is calculated by the following formula xj ,d yj ,d zj )。
And theta is an included angle between the AB axis of the laser and the XY axis of the platform coordinate system of the spatial linear vibration generating device. Position information (d) of the linear spatial vibration generated by the linear spatial vibration generating device is obtained xj ,d yj ,d zj ) Then, to (d) xj ,d yj ,d zj ) The velocity (v) of the linear vibration in space can be obtained by performing first and second differentiation xj ,v yj ,v zj ) And acceleration (a) xj ,a yj ,a zj ) And (4) information.
The space linear vibration measuring method based on the machine vision has the following advantages that:
(1) The method can accurately measure the space vibration information of the space linear vibration generating device through one camera.
(2) The method is portable and efficient, can quickly replace the measuring position and the measuring object, and measures the spatial linear vibration generated at any position.
(3) The cost of the measuring equipment used in the method is greatly reduced compared with the cost of the traditional measuring method.
Drawings
FIG. 1 is a schematic diagram of an apparatus according to an embodiment of the present invention.
FIG. 2 is a flow chart of the method of the present invention.
Detailed Description
Aiming at the defects of inaccurate measurement, fixed monitoring position and the like of the traditional vibration monitoring method, the invention provides a portable and efficient space vibration measuring method based on machine vision, which realizes accurate measurement of space vibration information at any position and specifically comprises the following steps: the invention is described in detail below with reference to the drawings and specific examples.
The device mainly includes: the device comprises a space linear vibration generating device (1), a laser (2), a laser receiving panel (3), a laser spot (4), a camera (5) and a data processing and displaying unit (6).
The space linear vibration generating device (1) generates space linear motion according to given parameters; the laser (2) is arranged in the direction of the space linear vibration generating device (1) opposite to the laser receiving panel (3), the laser receiving panel (3) receives two laser spots (4), and the space linear vibration generating device (1), the laser (2) and the two laser spots (4) have the same motion characteristic; the camera (5) is erected behind the laser receiving panel (3) and is used for acquiring motion information of the two laser spots (4); the data processing and displaying unit (6) is used for resolving the data collected by the camera (5) and outputting and storing the measuring result.
Fig. 2 is a flow chart of the invented machine vision-based spatial linear vibration measurement method. The measuring method mainly comprises the following steps:
s1, fixing a laser at the central position of a platform of a spatial linear vibration generating device, and ensuring that two mutually vertical laser beams emitted by the laser fixed on the platform form two circular light spots on a laser receiving panel in front of the vibration generating device;
s2, fixing a camera behind the laser receiving panel, determining the conversion relation between the laser receiving panel and a camera pixel coordinate system by utilizing camera calibration, and acquiring motion sequence images of two light spots by the camera;
s3, carrying out mean filtering on the image, searching the position of the maximum gray value of the image, rapidly positioning the area where the light spot is located, determining the region of interest of the image, and separating effective light spot information points and background noise information points in the light spot area through a threshold segmentation algorithm;
s4, carrying out Gaussian fitting on two effective information points of the light spots in each frame of image to obtain change information of the center position of the light spots, and resolving to obtain vibration information of the space linear vibration generating device;
the embodiment device uses a camera (OS 10-4K) with 900 ten thousand pixels and a frame rate of 1000fps to acquire the motion information of two light spots on a laser receiving panel, and the vibration displacement information of the spatial linear vibration generating device is obtained by resolving images acquired by the camera through a data processing and display unit;
in order to verify the measuring precision of the space linear vibration based on the machine vision, the method is compared with vibration measuring information of a laser interferometry in a range of 0.1-1.25 Hz, wherein the table 1 is the vibration displacement information of an X axis of a space linear vibration generating device measured by a specific implementation example of the method and the laser interferometry, the table 2 is the vibration displacement information of a Y axis of the space linear vibration generating device measured by the specific implementation example of the method and the laser interferometry, and the table 3 is the vibration displacement information of a Z axis of the space linear vibration generating device measured by the specific implementation example of the method and the laser interferometry. The maximum relative deviation of the vibration measurement of the method of the invention and the laser method is about 1%.
TABLE 1
TABLE 2
TABLE 3
The above description is a detailed description of an example embodiment of the invention and is not intended to limit the invention in any way. The invention is capable of many modifications, improvements and adaptations by those skilled in the art. Accordingly, the scope of the invention should be determined from the following claims.
Claims (6)
1. A space linear vibration measuring method based on machine vision is characterized in that: the measuring method comprises the following steps of,
s1, fixing a laser at the central position of a platform of a spatial linear vibration generating device, and ensuring that two mutually vertical laser beams emitted by the laser fixed on the platform form two circular light spots on a laser receiving panel in front of the vibration generating device;
s2, fixing a camera behind the laser receiving panel, determining the conversion relation between a coordinate system of the laser receiving panel and a pixel coordinate system of the camera by utilizing camera calibration, and acquiring motion sequence images of two light spots by the camera;
s3, carrying out mean filtering on the image, searching the position of the maximum gray value of the image, rapidly positioning the area where the light spot is located, determining the region of interest of the image, and separating effective light spot information points and background noise information points in the light spot area through a threshold segmentation algorithm;
and S4, carrying out Gaussian fitting on the two effective information points of the light spots in each frame of image to obtain the change information of the center position of the light spots, and calculating to obtain the vibration information of the space linear vibration generating device.
2. The machine vision-based spatial linear vibration measurement method according to claim 1, characterized in that:
horizontally fixing a laser at the center of a platform of a spatial linear vibration generating device, establishing a coordinate system O-XYZ of the spatial linear vibration generating device by taking the center O of the platform as an original point, establishing a laser coordinate system O-ABC by using two laser rays A and B and a normal C of a surface formed by the two laser rays A and B, mapping motion information of the spatial linear vibration generating device to a laser receiving panel through a laser beam, and presenting two circular laser spots on the laser receiving panel; and then, generating spatial linear vibration with different frequencies and amplitudes along the X axis, the Y axis and the Z axis of the motion platform of the spatial linear vibration generating device by controlling the motion platform of the spatial linear vibration generating device.
3. The machine vision-based spatial linear vibration measurement method according to claim 1, characterized in that:
a camera for shooting two light spots is fixed behind the laser receiving panel; firstly, acquiring a conversion relation H matrix of a coordinate system of a plane where light spots are located and a camera pixel coordinate by using a camera calibration method, and then acquiring j frames of light spot moving images F j (x,y)；
Wherein the parameter h 11 ,h 12 ,h 13 ,h 21 ,h 22 ,h 23 ,h 31 ,h 32 ,h 33 The internal and external parameters of the camera are expressed together.
4. The machine vision-based spatial linear vibration measurement method according to claim 1, characterized in that:
creating 5-by-5 mean value filtering convolution kernel g (x, y), and carrying out motion image F on the collected j frames of light spots j Convolving (x, y) with g (x, y) one by one to obtain processed j frames of spot moving images M j (x,y)，
At M j Finding out the maximum gray point of each frame in (x, y), determining the position of the light spot of the jth frame, expanding the region of interest R taking the point as the center and 20 x 20 as the jth frame, and utilizing the maximum between-class variance S 2 Determining an optimal gray threshold k capable of separating light spot information and background information in the R region;
wherein p is 1 M is the probability that the gray level of a certain pixel in the R region is less than the gray level threshold k G Is the mean value of the grays of the R region, m is the mean value of the grays with the gray level k,
wherein, mu i The probability when the gray level of the pixel point is i is obtained;
dividing the R region by using the optimal division threshold value to obtain a light spot information region R larger than a gray threshold value k 1 And background R less than a gray threshold k 2 Two regions.
5. The machine vision-based spatial linear vibration measurement method according to claim 1, characterized in that:
for light spot R 1 Set of pixel gray levels in region { R 1 (x, y) } fitting the center of the light spot by using a Gaussian fitting method
Wherein A is the gray peak value of the light spot, and the fitted central coordinate of the light spot is (x) center ,y center ),
Is x-axis standard deviation,. Sup.>
Is the y-axis standard deviation; for each frame image M j (x j ,y j ) R of (A) to (B) 1 Two facula centers (x) of the laser are obtained by the area using the formula (5) jL1, y jL1 )、(x jL2, y jL2 ) Using the following formulaCalculating spatial vibration information (d) of j-th frame of vibration generating device xj ,d yj ,d zj )；
Wherein theta is an included angle between an AB axis of the laser and an XY axis of a platform coordinate system of the spatial linear vibration generating device;
to (d) xj ,d yj ,d zj ) The velocity (v) of the linear vibration in space can be obtained by performing first and second differentiation xj ,v yj ,v zj ) And acceleration (a) xj ,a yj ,a zj ) And (4) information.
6. The machine-vision-based spatial linear vibration measurement method according to claim 1, characterized in that:
the device for realizing the method comprises the following steps: the device comprises a spatial linear vibration generating device (1), a laser (2), a laser receiving panel (3), a laser spot (4), a camera (5) and a data processing and displaying unit (6);
the space linear vibration generating device (1) generates space linear vibration according to given parameters; the laser (2) is arranged in the direction of the spatial linear vibration generating device (1) opposite to the laser receiving panel (3), the laser receiving panel (3) receives the two laser spots (4), and the spatial linear vibration generating device (1), the laser (2) and the two laser spots (4) have consistent motion characteristics; the camera (5) is erected behind the laser receiving panel (3) and is used for acquiring motion information of the two laser spots (4); the data processing and displaying unit (6) is used for resolving the data collected by the camera (5) and outputting and storing the measuring result.
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