CN110702007B - A three-dimensional measurement method of line structured light based on MEMS scanning galvanometer - Google Patents

Abstract

The invention belongs to the technical field of robot vision three-dimensional measurement, and discloses a line structured light three-dimensional measurement method based on a MEMS scanning galvanometer. The method includes the following steps: (a) setting the scanning range of the MEMS scanning galvanometer and the interval angle between the light spots; (b) using a two-dimensional checkerboard target to define the connection between the laser emission point A and each light spot to form (c) The MEMS scanning galvanometer scans the object to be measured to establish the correspondence between the points on the image and the light points; (d) Calculate the line formed by connecting any point P on the straight line image and the camera optical center B The intersection of the straight line PB and the light AO, the coordinates of the intersection are the coordinates of the required light spot O. In this way, the coordinates of all light spots on the surface of the object to be measured are obtained, that is, the three-dimensional measurement of the object to be measured is realized. The present invention eliminates the influence of inaccurate extraction of the center of the light bar due to overexposure of the light bar when measuring the mixed reflective surface with linear structured light, and improves the three-dimensional measurement accuracy.

Description

A three-dimensional measurement method of line structured light based on MEMS scanning galvanometer

technical field

The invention belongs to the technical field of three-dimensional measurement of robot vision, and more particularly relates to a three-dimensional measurement method of line structured light based on a MEMS scanning galvanometer.

Background technique

In recent years, with the development of industrial technology, the measurement requirements for real-world three-dimensional structures have become more and more extensive. Among them, in the aspect of structured light, point structured light technology, line structured light technology and surface structured light technology are mainly developed. Structured light measurement obtains three-dimensional information on the surface of the object to be measured, and is generally based on the principle of trigonometry. The line structured light measurement method generally uses three steps to obtain the measured target information: ① Determine the pose relationship between the line light plane and the camera coordinate system through calibration; ② The center of the light strip is extracted to determine the projection point of the object surface line light on the camera imaging surface; ③ Trigonometry calculates three-dimensional point coordinates.

The three-dimensional point coordinates of the surface of the diffuse reflection object in the camera coordinate system can be accurately obtained by using the line structured light. However, when the surface of the object exhibits mixed reflection (both diffuse reflection and specular reflection) surface characteristics, the linear structured light reduces the measurement error due to the large extraction error of the center of the light strip, and even cannot obtain effective measurement results.

The reason for the large error in the extraction of the center of the light strip is that the light strip is overexposed due to the presence of specular reflection and mutual reflection when the line laser is irradiated on the mixed reflection display. At present, the non-coding nature of line lasers is the main reason for the poor performance of line structured light measurement methods in measuring hybrid reflective surfaces.

SUMMARY OF THE INVENTION

In view of the above defects or improvement requirements of the prior art, the present invention provides a three-dimensional measurement method of linear structured light based on a MEMS scanning galvanometer. The light equation of the target calibration laser emission point and the light point determines the light direction, reduces the computational complexity, eliminates the error of extracting the center of the light bar, and improves the measurement accuracy.

In order to achieve the above object, according to the present invention, a three-dimensional measurement method of line structured light based on MEMS scanning galvanometer is provided, and the method comprises the following steps:

(a) Set the scanning range of the MEMS scanning galvanometer and the interval angle between the light spots, divide the scanning range equally according to the interval angle, and number the divided light spots to obtain each light spot point number;

(b) Place the two-dimensional checkerboard target in the scanning area of the MEMS scanning galvanometer, and use the optical knife plane calibration method to calibrate the MEMS scanning galvanometer, so as to obtain the connection between the laser emission point A and each light spot on the MEMS scanning galvanometer The ray equation formed by the line;

(c) Remove the two-dimensional checkerboard and place the measuring object in the scanning field of the MEMS scanning galvanometer, set the relationship between the brightness of each light spot and the light spot number, and determine the The brightness is set, and the MEMS scanning galvanometer scans the surface of the object to be measured according to the set brightness, scanning range and interval angle, so that a straight line with different brightness is formed on the surface of the object to be measured, and the camera captures the straight line to obtain a straight line image , and use the straight line image to establish the correspondence between the point on the image and the light spot;

(d) For any point P on the straight line image obtained in step (c), obtain the surface of the object to be measured and the arbitrary point according to the correspondence between the point on the straight line image obtained in step (c) and the light spot For the light point O corresponding to P, find the light equation AO where the point O is located according to all the straight line equations obtained in step (b), and calculate the intersection point of the straight line PB formed by the connection between the point P and the optical center B of the camera and the light AO, The coordinates of the intersection point are the coordinates of the required light spot O. In this way, the coordinates of all light spots on the surface of the object to be measured are obtained, that is, the three-dimensional measurement of the object to be measured is realized.

Further preferably, in step (b), the MEMS scanning galvanometer is calibrated by the optical knife plane calibration method, preferably according to the following steps:

(b1) The camera shoots the two-dimensional chessboard target, and uses the photographed chessboard target image to obtain the plane equation of the plane of the two-dimensional chessboard target in the camera coordinate system;

(b2) The laser emission point A on the MEMS scanning galvanometer emits laser light to scan on the surface of the two-dimensional checkerboard target according to the scanning range and light spot interval angle set in step (a), and the camera shoots and scans the surface of the two-dimensional checkerboard target. An image of an arbitrary light spot Q, so as to obtain the pixel coordinate Q' of any light spot on the image in the camera coordinate system;

(b3) using the pixel coordinate Q' obtained in the step (b2) to intersect the plane equation, thereby obtaining the coordinate Q ₁ of the arbitrary light spot Q in the two-dimensional chessboard target under the camera coordinate system;

(b4) Change the position of the two-dimensional chessboard, and repeat steps ((b2) and (b3), so as to obtain the coordinate Q ₂ of the arbitrary light point Q in the two-dimensional chessboard target in the camera coordinate system, and the straight line Q ₁ Q ₂ are the ray equations formed by the connection line between the laser emission point A and the light point Q; in this way, the ray equation formed by the connection line from the laser emission point to each light point is obtained.

Further preferably, in step (b2), when the MEMS scanning galvanometer scans the two-dimensional chessboard target, the brightness of each light spot is set as the maximum brightness value, then any light on the image in the camera coordinate system is obtained. The pixel coordinate Q' of the point is obtained by extracting the light bar center algorithm.

Further preferably, in step (c), the relationship between the setting of the brightness of each light spot and the irradiation angle is preferably performed according to the following relationship:

是第j个周期在相移n下的亮度。where n is the phase shift, which is an integer, T _j is the jth cycle, j is the number of cycles, N is the total number of cycles, A is the set luminance mean, B is the luminance amplitude, and x is the number of the light spot ,

is the luminance of the jth period at phase shift n.

Further preferably, in step (c), the use of the straight line image to establish the correspondence between the point on the image and the light spot preferably follows the following steps:

(c1) set the values of phase shift n and period j, and calculate the winding phase φ _{j corresponding to the period T j ;}

(c2) Solve the absolute phase φ that reflects the relationship between the point and the light spot on the straight line image by using the respective winding phases of all periods, so as to obtain the corresponding relationship between the point and the light spot on the image.

Further preferably, in step (c1), when n=0, 1, 2, 3, j=1, 2, 3,

The winding phase is preferably carried out according to the following expression:

Absolute phase is performed according to the following expression:

in,

Further preferably, after step (d), it is also necessary to verify the O coordinate of the light spot, preferably the following method is used:

(d1) Fitting the light equation formed by the connection between the laser emission point and all the light points on the MEMS scanning galvanometer obtained in step (b) into a plane, that is, the line light plane;

(d2) Judging whether the coordinates of the light spot O are on the line light plane, on the line light plane, the light spot O coordinates are qualified, otherwise, the light spot O coordinates are unqualified.

In general, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects.

1. The present invention designs a line structured light three-dimensional measurement method based on a MEMS scanning galvanometer. The MEMS scanning galvanometer and a camera form a line structured light measurement system to obtain the three-dimensional point cloud information of the measured target. The brightness of the light spots in each scanning direction realizes the encoding of the scanning direction, and the corresponding scanning direction can be determined by decoding the light bar pattern obtained by the camera, so that the direction of each point on the light bar can be determined, so the overexposure of the light bar can be eliminated. The influence of inaccurate extraction of the center of the light strip improves the accuracy of 3D measurement;

2. In this application, different light spots are distinguished by setting the brightness of each light spot, and the two-dimensional checkerboard target is used to calibrate the light equation of the laser emission point and the light spot to determine the light direction, reduce the computational complexity, and eliminate the extraction of light bars. The error of the center improves the measurement accuracy.

Description of drawings

FIG. 1 is a schematic diagram of the principle of a three-dimensional measurement method of line structured light based on a MEMS scanning galvanometer constructed according to a preferred embodiment of the present invention.

Throughout the drawings, the same reference numbers are used to refer to the same elements or structures, wherein:

1-Camera, 2-MEMS scanning galvanometer, 3-Object to be measured, 4-Linear light plane, 5-Light direction.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

A three-dimensional measurement method of line structured light based on MEMS scanning galvanometer, comprising the following steps:

Step 1: Determine the ray equation formed by the laser emission point and the light point, and the line light plane formed by all the ray equations by the light knife plane calibration method, which includes the following steps:

Step 1: Place the two-dimensional target in the field of view of camera 1, the camera shoots an image of the two-dimensional target, and solves the camera coordinates and chessboard of the two-dimensional target in the camera coordinate system by the PnP (abbreviation of pespective-n-point) method The translation matrix and rotation matrix between the coordinate systems where the grid is located. The z-axis component of the rotation and rotation is the normal vector of the plane equation. The three-dimensional point coordinates of the translation matrix are on the plane of the checkerboard in the camera coordinate system. The plane equation of the checkerboard plane of the target in the camera coordinate system;

Step 2: Keep the pose of the two-dimensional target in Step 1, project the brightness coding line on the two-dimensional target through the MEMS scanning vibrating mirror, the brightness of all scanning points are encoded as the maximum brightness value, and the camera shoots the two-dimensional target with the brightness coding line on the surface pattern;

Step 3: Extract the coordinates of the center point of the brightness coding line of the two-dimensional target pattern in the camera in Step 2 by the light bar center algorithm;

Step 4: The straight line formed by the connection between the center point and the optical center of the camera intersects the plane equation of the checkerboard plane obtained in Step 1 in the camera coordinate system. The intersection point is the light spot on the two-dimensional target chessboard in the camera coordinate system. coordinate of;

Step 5: Change the position and angle of the two-dimensional target, and repeat Step1, Step2, Step3

Step 6: Perform plane fitting on the center coordinates of the brightness coding line on the two-dimensional target at different positions, and the ray equation formed by the connection between the laser emission point A and the light spot; The ray equation M formed by the connecting lines.

Step 2: The MEMS scanning galvanometer is single-point scanning, which can scan rapidly and continuously in the scanning direction, and encode the brightness of the light spot at each scanning position. The brightness encoding method adopts a 4-step phase shift encoding method (formula 1), which can be The surface of the object forms a brightness-encoded line. The brightness code line projected by the MEMS scanning galvanometer 2 is irradiated on the measured object, and the camera 1 captures the brightness code line on the surface 3 of the measured object.

是第j个周期在相移n下的亮度，本实施例中，用三个不同的周期对光点亮度进行编码，MEMS扫描振镜的扫描范围为60度，每隔0.025度扫描一个光点，则x的取值范围为1到2400；N取值为4,n是相移。Among them, n is the phase shift, which is an integer, T _j is the jth period, j is the number of periods, A is the set brightness mean, B is the brightness amplitude, x is the number of the light spot,

is the brightness of the jth cycle under phase shift n. In this embodiment, three different cycles are used to encode the brightness of the light spot. The scanning range of the MEMS scanning galvanometer is 60 degrees, and a light spot is scanned every 0.025 degrees. , the value of x ranges from 1 to 2400; the value of N is 4, and n is the phase shift.

Then, the camera shoots 12 luminance coding lines projected by the MEMS scanning galvanometer according to formula (2), and solves the four images of each coding period T _j according to formula (3) to obtain the winding phase.

Among them, φ _j represents the winding phase corresponding to the period T _j .

Finally, the absolute phase φ is determined according to φ ₁ , φ ₂ , and φ ₃ , and the absolute phase reflects the correspondence between the pixel point and the light spot position.

Step 3: According to the light spot position (light direction) determined by the absolute phase φ and the camera pixel correspondence, determine the three-dimensional coordinates of the measured point by trigonometry;

Step 1: The camera shoots 12 brightness-encoded line images projected by the MEMS scanning galvanometer to the surface of the object to be measured, and decodes the pixel and the light spot position (light direction) correspondence through multi-frequency heterodyne decoding;

Step 2: The line connecting the camera pixel coordinates and the optical center is represented as line 1, and the direction of the light where the light spot is located is represented as line 2. Calculate the intersection of line 1 and line 2. When line 1 and line 2 do not intersect, calculate the Plumb point.

Step 4: Eliminate wrong points. Since the light spot projected by the laser transmission on the surface of the object to be measured is relatively large, many pixels correspond to one light spot, so that there are many P points. Therefore, many incorrect points will be generated, and The closer it is to the plane, the more correct it is.

Step 1: Calculate the distance between the three-dimensional point coordinates obtained in 3 and the plane square M obtained in 2;

Step 2: Set the threshold value T. When the distance between the three-dimensional point coordinates and the plane M is greater than T, it is judged as an error point, and when the distance is less than or equal to T, it is judged as a correct point.

In summary, the present invention provides a three-dimensional measurement method for linear structured light based on a MEMS scanning galvanometer. A linear structured light measurement system is formed by a one-dimensional coded MEMS scanning galvanometer and a camera, and the light bar pattern is encoded to determine the light. The direction of each point of the strip is eliminated, thereby eliminating the influence of inaccurate extraction of the center of the strip due to overexposure of the strip, and improving the accuracy of 3D measurement.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (5)

1. A three-dimensional measurement method of line structured light based on MEMS scanning galvanometers is characterized by comprising the following steps:

(a) setting the scanning range of the MEMS scanning galvanometer and the interval angle between the light spots, equally dividing the scanning range according to the interval angle, and numbering the equally divided light spots so as to obtain the number of each light spot;

(b) placing a two-dimensional chessboard target in a scanning domain of an MEMS scanning galvanometer, and calibrating the MEMS scanning galvanometer by adopting a light knife plane calibration method so as to obtain a light ray equation formed by connecting a laser emission point A to each light spot on the MEMS scanning galvanometer;

the MEMS scanning galvanometer is calibrated by adopting an optical knife plane calibration method, and the calibration is carried out according to the following steps:

(b1) shooting a two-dimensional chessboard target by a camera, and obtaining a plane equation of a plane of the two-dimensional chessboard target in a camera coordinate system by utilizing a shot chessboard target image;

(b2) scanning the two-dimensional chessboard target surface by laser emitted by a laser emitting point A on the MEMS scanning galvanometer according to the scanning range and the light spot interval angle set in the step (a), and shooting an image of any light spot Q scanned on the two-dimensional chessboard target surface by a camera to obtain a pixel coordinate Q' of any light spot on the image in a camera coordinate system;

when the MEMS scanning galvanometer scans a two-dimensional chessboard target, the brightness of each light spot is set as the maximum brightness value, and the pixel coordinate Q' of any light spot on the image in the camera coordinate system is obtained by adopting the light bar center algorithm;

(b3) intersecting the pixel coordinate Q' obtained in the step (b2) with the plane equation to obtain the coordinate Q of the arbitrary light point Q in the two-dimensional chessboard target under the camera coordinate system₁；

(b4) Changing the position of the two-dimensional chessboard, repeating the steps ((b2) and (b3) to obtain the coordinate Q of the arbitrary point Q in the two-dimensional chessboard target under the camera coordinate system₂Straight line Q₁Q₂The bar is a light ray equation formed by connecting the laser emission point A and the light spot Q; in this way, a ray equation formed by connecting a laser emission point to each light spot is obtained;

(c) removing the two-dimensional chessboard, placing an object to be measured in a scanning domain of an MEMS scanning galvanometer, setting a relational expression between the brightness of each light spot and the light spot number, setting the brightness of each light spot according to the relational expression, scanning the surface of the object to be measured by the MEMS scanning galvanometer according to the set light spot brightness, scanning range and interval angle, forming a straight line with different brightness on the surface of the object to be measured, shooting the straight line by a camera to obtain a straight line image, and establishing a corresponding relation between the light spot and the point on the image by using the straight line image;

(d) and (c) for any point P on the linear image obtained in the step (c), obtaining a light point O corresponding to the surface of the object to be measured and the any point P according to the corresponding relation between the point on the linear image obtained in the step (c) and the light point, finding a ray equation AO where the point O is located in all the linear equations obtained in the step (B), calculating the intersection point of a straight line PB formed by the connection line of the point P and the optical center B of the camera and the ray AO, wherein the intersection point coordinate is the needed light point O coordinate, and obtaining the coordinates of all the light points on the surface of the object to be measured in such a way, namely realizing the three-dimensional measurement of the object to be measured.

2. The method for three-dimensionally measuring line structured light based on MEMS scanning galvanometer of claim 1, wherein in step (c), the setting of the relationship between the brightness of each spot and the illumination angle is performed according to the following relationship:

where n is a phase shift, is an integer, T_jIs the jth period, j is the number of periods, N is the total number of periods, a is the set luminance mean, B is the luminance amplitude, x is the number of spots,

is the luminance of the jth period at the phase shift n.

3. The method for three-dimensional measurement of line structured light based on MEMS scanning galvanometer of claim 1, wherein in step (c), said using the line image to establish correspondence between points on the image and the light spots is according to the following steps:

(c1) setting the values of phase shift n and period j, and calculating period T_jCorresponding winding phase phi_j；

(c2) And solving an absolute phase phi reflecting the relationship between the point and the light spot on the linear image by utilizing the winding phases corresponding to all the periods respectively so as to obtain the corresponding relationship between the point and the light spot on the image.

4. The linear structured light three-dimensional measurement method based on the MEMS scanning galvanometer of claim 3, wherein in step (c1), when n is 0,1,2,3, j is 1,2,3,

the winding phase proceeds according to the following expression:

the absolute phase proceeds as follows:

wherein,

5. the method for three-dimensional measurement of line structured light based on MEMS scanning galvanometer of claim 1, wherein after step (d), the O coordinate of the light point is verified by the following method,

(d1) fitting a light equation formed by connecting the laser emission point on the MEMS scanning galvanometer to all light spots obtained in the step (b) into a plane, namely a linear light plane;

(d2) and judging whether the coordinates of the light spot O are on the linear light plane, if so, determining that the coordinates of the light spot O are qualified, otherwise, determining that the coordinates of the light spot O are unqualified.

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