CN113421309A - Single-camera cross-visual-field distance measurement platform calibration method, distance measurement method and system - Google Patents
Single-camera cross-visual-field distance measurement platform calibration method, distance measurement method and system Download PDFInfo
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Abstract
The invention discloses a calibration method, a distance measurement method and a distance measurement system for a single-camera cross-visual-field distance measurement platform. The calibration method comprises the following steps: obtaining coordinates of the image center point of a plurality of (for example, 12, the present invention is described by taking 12 as an example) positions of the platform and corresponding platform coordinates; and solving the transformation matrix (calibration matrix) to obtain the relation between the image coordinate and the platform coordinate. The distance measurement method comprises the following steps: calculating the platform coordinate of the ranging endpoint through the calibration matrix according to the deviation between the pixel coordinate of the ranging endpoint and the pixel coordinate of the image center; and solving the distance between the ranging points according to the platform coordinates of the ranging endpoint. The invention realizes the vision of a single camera and a cross-visual field machine, and uniformly calibrates the platforms with a plurality of visual field ranges to obtain a uniform calibration matrix, thereby simultaneously carrying out image taking measurement of a plurality of scattered areas through one camera, realizing the measurement of large distance in a large area, avoiding the problems of large measurement error and pixel waste under the condition of large visual field of one camera and avoiding the cost problem of small visual fields of a plurality of cameras. The invention has simple structure, convenient use, low cost and good application value.
Description
Technical Field
The invention relates to the technical field of machine vision, in particular to a distance measuring platform calibration method, a distance measuring method and a distance measuring system.
Background
With the development of manufacturing industry, workpiece measurement and product detection by using a machine vision technology become important means for improving production efficiency and product quality. Currently, there are mature solutions for measuring small-sized workpieces within a single camera field of view, and for measuring large-sized workpieces, either a single large-field-of-view camera or multiple small-field-of-view cameras are used, which both increase the cost of the measurement system and reduce the accuracy of the measurement. Therefore, it is a practical need to measure large-sized workpieces across the field of view with a single camera. However, since the workpiece is in different fields of view of a single camera, and the distance measurement end point of the workpiece is located in different images, it is critical to solve the problem to accurately obtain the world coordinate of the distance measurement end point through technical means.
Disclosure of Invention
Aiming at the actual production needs, the invention provides a calibration method, a ranging method and a ranging system for a single-camera cross-visual-field ranging platform.
The invention discloses a calibration method of a single-camera cross-visual-field distance measuring platform, which comprises the following steps:
step 1, a calibration plate is used and placed on a platform, and the size of the calibration plate needs to be capable of covering the ranging range of the ranging platform. A moving platform, which respectively aligns a plurality of dots (such as 12 dots, the invention is described by taking 12 dots as an example) on the calibration plate to the optical center of the camera, and each alignment point controls the camera to shoot an image;
step 3, selecting a dot image at the upper left corner of the calibration plate as a reference image, and respectively calculating pixel coordinates of the center points of the other 11 images relative to the center point of the reference image according to the center distance of dots on the calibration plate;
and 4, solving a transformation matrix (calibration matrix) according to the pixel coordinates of the central point of the 12 groups of images and the platform coordinates corresponding to the pixel coordinates.
The invention discloses a single-camera cross-visual-field distance measuring platform distance measuring method, which comprises the following steps:
step 1, moving a platform according to the distance measurement requirement, enabling one end point to be measured to enter the vicinity of the camera view center, controlling a camera to shoot an image, measuring the image coordinate deviation of the end point and the image center point, recording the platform coordinate value, and calculating the platform coordinate value corresponding to the distance measurement end point by using a transformation matrix (calibration matrix) according to the deviation value;
step 3, according to the platform coordinates corresponding to the two end points, the distance between the two end points can be calculated, and the distance measurement requirement is met;
the invention discloses a machine vision ranging system, which comprises:
calibrating a plate: the size of the range finding platform can cover the range finding range of the range finding platform, 3 rows and 4 columns of 12 round dots with the same size are distributed on the range finding platform, and the row spacing and the column spacing of the round dots are required to be equal;
a distance measuring platform: the distance measuring platform is used for bearing a workpiece, and a light source system is arranged below the distance measuring platform;
a camera: the camera is a small-field single camera and is arranged above the ranging platform, and the camera is connected with the computer and is used for acquiring a calibration plate image and a workpiece image;
a computer: the computer obtains the pixel coordinates of the optical center of the camera and the corresponding coordinates of the distance measuring platform when the platform moves across the visual field according to the calibration plate image shot by the camera, then the mapping relation between the pixel coordinates of the optical center of the camera and the coordinates of the platform is obtained, the coordinates of the distance measuring platform corresponding to the pixel coordinates of the distance measuring end points of the workpiece are calculated through the mapping relation, and further the distance between the distance measuring end points of the workpiece is calculated.
The invention realizes the vision of a single camera and a cross-visual field machine, and uniformly calibrates the platforms with a plurality of visual field ranges to obtain a uniform calibration matrix, thereby simultaneously carrying out image taking measurement of a plurality of scattered areas through one camera, realizing the measurement of large distance in a large area, avoiding the problems of large measurement error and pixel waste under the condition of large visual field of one camera and avoiding the cost problem of small visual fields of a plurality of cameras. The invention has simple structure, convenient use, low cost and good application value.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:
FIG. 1 is a schematic diagram illustrating relative positions of a calibration plate, a camera, and a stage according to an embodiment;
FIG. 2 is a schematic diagram of a dot image and an image coordinate system according to an embodiment;
FIG. 3 is a diagram illustrating a ranging method according to a second embodiment;
FIG. 4 is a schematic diagram of a machine vision ranging system according to a third embodiment.
Detailed Description
Example one
The embodiment discloses a calibration method for a single-camera cross-visual-field distance measuring platform. Fig. 1 is a schematic diagram showing the relative positions of the calibration plate, the camera and the platform, and a world coordinate system XOY is established according to the "right-hand rule". Wherein the camera is stationary and the calibration plate is placed on the platform and moved along the X-direction and the Y-direction together with the platform.
The calibration method for the single-camera cross-visual-field distance measuring platform provided by the embodiment comprises the following steps:
step 1, preparing 1 calibration board with a plurality of dots (for example, 12 dots, the invention is described by taking 12 dots as an example), wherein the size of the calibration board is required to be capable of covering the ranging range of the ranging platform, the distance between the columns of the centers of adjacent dots is C, and the distance between the rows of the centers of adjacent dots is R. The column pitch C or the row pitch R should be smaller than the camera field of view, which facilitates the calculation of the calibration board tilt angle in step 6 of this embodiment. The calibration plate can be a standard calibration plate provided by a third party, and can also be manufactured according to the following steps and requirements:
(1) preparing a piece of printing paper, wherein the size of the printing paper can cover the range measurement range of the range measurement platform;
(2) as shown in fig. 1, 12 solid dots having the same radius are printed on the printing paper, and the 12 dots are arranged in 3 rows and 4 columns. The line spacing of the dots is equal to R, the column spacing is also equal to C, and the line spacing R and the column spacing C can be equal or unequal;
(3) in order to ensure the calibration precision, the roundness error and the dot spacing error of dots are required to be within a certain range;
(4) after printing, measuring and recording the line spacing R and the column spacing C of dots on printing paper;
step 3, moving the platform after the platform is reset, and sequentially aligning the 12 dots on the calibration plate to the optical center of the camera approximately, wherein each pair of aligned dots controls the camera to shoot an image;
step 4, as shown in fig. 2 (a), selecting a dot image a at the upper left corner of the calibration plate as a reference image to establish a pixel coordinate system xoy, and fixing the origin of the coordinate system at the upper left corner of the image;
step 5, respectively measuring pixel coordinates (px, py) of the circle center of a dot closest to the center of the image in 12 images, and respectively recording platform coordinates (X, Y) corresponding to each image;
step 6, moving the platform, optionally placing two adjacent dots on the calibration plate in the camera view field, and controlling the camera to shoot an image C as shown in fig. 2 (b);
and 7, respectively calculating the pixel coordinates of the center points of the other 11 images in the image coordinate system xoy according to the center distance of the circular points on the calibration plate and the inclination angle of the calibration plate relative to the camera. Taking the top left corner dot image a and the row 2 and column 3 dot image B shown in fig. 2 as an example, the derivation process of the calculation formula for solving the pixel coordinate of the center point of the image B is as follows:
(1) as shown in fig. 2 (b), when the pixel coordinates of the circle center p2 in the C image are (x2, y 2) and the pixel coordinates of the circle center p3 in the C image are (x 3, y 3), then:
the tilt angle of the calibration plate to the camera θ = arctg ((y2-y1)/(x2-x1))
(2) As shown in fig. 2 (a), the pixel coordinates of the center point c0 of the top left dot image (reference image) are measured as (x 0, y 0), the pixel coordinates of the dot center p0 are measured as (px 0, py 0), the length from the dot center p1 of the row 2 and column 3 dot images to the left side of the image is measured as px1 pixels, and the length from the dot center to the upper side of the image is measured as py1 pixels. Given the resolution of the image as rc, the column spacing of the dots as C, and the row spacing as R, then:
the distance from the circle center p0 of the dot to the circle center p1 of the dot
Projection Lx = d ∑ cos θ of distance d in image coordinate system x direction
Projection Ly = d @ sin θ of distance d in image coordinate system y direction
X-direction pixel coordinate x1 = x0 + of center point c1 of image B (Lx + px0-px 1)
Y-direction pixel coordinate y1 = y0 + (Ly + py0-py 1) of center point c1 of image B
And 8, calculating the pixel coordinate of the central point of each dot image by using the same method as the step 7. Thus, 12 groups of image center point pixel coordinates and platform coordinates corresponding to the image center point pixel coordinates can be obtained;
and 9, fitting a transformation matrix (calibration matrix) by a polynomial by adopting a least square method according to the obtained 12 groups of coordinates. The transformation relation between the pixel coordinates (X, Y) of the image center point and the platform coordinates (X, Y) is as follows:
where R is a rotation matrix and M is a translation matrix. The above formula can be expanded as follows:
wherein a, b, c, d, e and f are required coefficients, and the 6 coefficients form a transformation matrix (calibration matrix). 6 unknowns and 24 equations which are an over-determined equation, and the optimal solution is obtained by applying a least square method, so that a transformation matrix (calibration matrix) T is obtained, and coefficients a, b, c, d, e and f are obtained.
Example two
The embodiment provides a single-camera cross-field ranging platform ranging method, which comprises the following steps:
step 1, as shown in fig. 3, the workpiece AB is placed on the platform, and the distance between the end point a and the end point B exceeds a visual field of the camera. In order to measure A, B distance, moving the platform to make the A end point to be measured enter near the center of the camera visual field, and controlling the camera to shoot an image;
and 2, measuring the pixel coordinate deviations delta X1 and delta Y1 between the A endpoint and the image center point c1, and recording the coordinate values (X1, Y1) of the platform at the moment. And calculating platform coordinate values (X1 + delta X1, Y1+ delta Y1) corresponding to the distance measuring endpoint A by using a transformation matrix (calibration matrix) T according to the deviation values delta X1 and delta Y1, wherein:
ΔX1 = a﹒Δx1 + b﹒Δy1，ΔY1 = c﹒Δx1 + d﹒Δy1
step 3, obtaining platform coordinate values (X2 + delta X2, Y2+ delta Y2) corresponding to the other end point B by the same method;
and 4, according to the platform coordinates corresponding to the endpoint A and the endpoint B, the distance D between the two endpoints can be obtained, and the distance measurement requirement is realized as follows:
EXAMPLE III
Fig. 4 is a schematic diagram of the machine vision ranging system in this embodiment. The machine vision ranging system disclosed by the embodiment comprises a calibration plate, a ranging platform, a camera, a computer, a PLC (programmable logic controller), a servo driving system and the like. The calibration plate is used for calibrating the mapping relation between the image pixel coordinates and the platform coordinates, and the size of the calibration plate can cover the ranging range of the ranging platform. The calibration plate can be a standard calibration plate provided by a third party and can be customized according to the size of the ranging platform. The distance measuring platform is used for bearing the workpiece. The camera is arranged above the ranging platform, is connected with the computer and is used for acquiring the image of the calibration plate and the image of the workpiece. The computer adopts an industrial personal computer with multiple serial ports and multiple network ports. During calibration, the computer obtains the pixel coordinates of the optical center of the camera and the corresponding coordinates of the distance measuring platform when the platform moves across the visual field according to the calibration plate image shot by the camera, and then the mapping relation between the pixel coordinates of the optical center of the camera and the coordinates of the platform is obtained. During ranging, the computer calculates the ranging platform coordinate corresponding to the pixel coordinate of the workpiece ranging endpoint by using the calibration matrix, and further calculates to obtain the distance between the workpiece ranging endpoints. And the PLC controls the servo system to drive the ranging platform to move to the designated position according to the request signal of the mobile ranging platform sent by the computer.
The above description is only an embodiment of the present invention, and is not intended to limit the present invention. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent, replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (3)
1. A calibration method for a single-camera cross-visual-field distance measurement platform is characterized by comprising the following steps:
step 1, using a calibration plate, placing the calibration plate on a platform, wherein the size of the calibration plate is required to cover the ranging range of a ranging platform;
a moving platform, which respectively aligns a plurality of dots (such as 12 dots, the invention is described by taking 12 dots as an example) on the calibration plate to the optical center of the camera, and each alignment point controls the camera to shoot an image;
step 2, respectively measuring the pixel coordinates of the circle center of a dot nearest to the optical center of the camera in 12 images, and respectively recording the platform coordinates corresponding to each image;
step 3, selecting a dot image at the upper left corner of the calibration plate as a reference image, and respectively calculating pixel coordinates of the center points of the other 11 images relative to the center point of the reference image according to the center distance of dots on the calibration plate;
and 4, solving a transformation matrix (calibration matrix) according to the pixel coordinates of the central point of the 12 groups of images and the platform coordinates corresponding to the pixel coordinates.
2. A single-camera cross-field ranging platform ranging method based on the platform calibration method of claim 1, comprising:
step 5, moving the platform according to the distance measurement requirement, enabling one end point to be measured to enter the vicinity of the camera view center, controlling the camera to shoot an image, measuring the image coordinate deviation of the end point and the image center point, recording the platform coordinate value, and calculating the platform coordinate value corresponding to the distance measurement end point by using a transformation matrix (calibration matrix) according to the deviation value;
step 6, acquiring a platform coordinate corresponding to the other end point by using the method in the step 5;
and 7, according to the platform coordinates corresponding to the two end points, the distance between the two end points can be calculated, and the distance measurement requirement is met.
3. A machine vision ranging system, comprising:
calibrating a plate: the size of the range finding platform can cover the range finding range of the range finding platform, 3 rows and 4 columns of 12 round dots with the same size are distributed on the range finding platform, and the row spacing and the column spacing of the round dots are required to be equal;
a distance measuring platform: the distance measuring platform is used for bearing a workpiece, and a light source system is arranged below the distance measuring platform;
a camera: the camera is a small-field single camera and is arranged above the ranging platform, and the camera is connected with the computer and is used for acquiring a calibration plate image and a workpiece image;
a computer: the computer obtains the pixel coordinates of the optical center of the camera and the corresponding coordinates of the distance measuring platform when the platform moves across the visual field according to the calibration plate image shot by the camera, then the mapping relation between the pixel coordinates of the optical center of the camera and the coordinates of the platform is obtained, the coordinates of the distance measuring platform corresponding to the pixel coordinates of the distance measuring end points of the workpiece are calculated through the mapping relation, and further the distance between the distance measuring end points of the workpiece is calculated.
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| CN114331924A (en) * | 2022-03-15 | 2022-04-12 | 四川焱飞科技有限公司 | Large workpiece multi-camera vision measurement method |
| CN115100225A (en) * | 2022-05-10 | 2022-09-23 | 桂林量具刃具有限责任公司 | Method and device for determining error field of camera view field, electronic equipment and medium |
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