Galvanometer rotation axis calibration method and system for rotary line laser scanning three-dimensional measurement

Abstract

The application belongs to the technical field of line laser three-dimensional measurement, and particularly discloses a galvanometer rotating shaft calibration method and system for rotary line laser scanning three-dimensional measurement, which comprises the following steps: laser emitted by a line laser is directly incident on a three-dimensional calibration plate, an auxiliary camera is used to collect incident laser stripes to obtain an incident laser plane under the auxiliary camera measurement coordinate system; the laser emitted by the line laser is reflected to the three-dimensional calibration plate through a galvanometer, the galvanometer is controlled to rotate at multiple angles, a main camera is used to collect reflected laser stripes to obtain a reflected laser plane under the main camera measurement coordinate system; the incident laser plane is converted to the main camera measurement coordinate system based on the relative pose relationship between the auxiliary camera and the main camera; and then the galvanometer mirror surface equation corresponding to different galvanometer rotating angles is calculated to determine the galvanometer rotating shaft line. The application can compensate for the system error of the installation error of the line laser incident position and the relative rotating shaft offset of the galvanometer mirror surface, and improve the galvanometer rotating shaft calibration precision.

Description

Technical Field

[0001] This invention belongs to the field of line laser three-dimensional measurement technology, and more specifically, relates to a galvanometer axis calibration method and system for rotary line laser scanning three-dimensional measurement. Background Technology

[0002] Line laser 3D measurement is a non-contact, monocular active measurement method with advantages such as high measurement accuracy and strong resistance to ambient light interference. It is widely used in various scenarios such as reverse engineering of industrial parts, dimensional measurement, defect detection, and visual positioning. Traditional line laser sensors consist of a line laser emitter and an industrial camera, and can only calculate 3D points based on a single laser line. In practical applications, a guide rail is often required to expand the scanning range of the line laser sensor, resulting in a complex overall structure and poor versatility. To increase the flexibility of line laser sensors, a new approach is to add a galvanometer as a rotating structure to the original structure. The line laser is projected onto the surface of the galvanometer, and the laser line moves with the rotation of the galvanometer surface, thereby expanding the single-frame scanning range of the line laser sensor. The key to calibrating this type of rotating scanning line laser sensor lies in the orientation calibration of the galvanometer rotation axis. Ideally, the intersection of the incident laser plane and the galvanometer surface should coincide with the rotation axis. In reality, due to the thickness of the galvanometer itself, the rotation axis is not on the surface of the reflecting mirror. Therefore, in actual assembly, the intersection line may be parallel, intersecting, or out of plane with the rotation axis, which greatly affects the calibration accuracy of the measurement system.

[0003] To this end, many scholars have conducted in-depth research on the calibration of line laser rotating scanning measurement systems. Some scholars have proposed to improve the assembly accuracy so that the intersection of the reflected laser plane is approximated as the rotation axis of the galvanometer, ignoring the error between the theoretical model and the actual assembly situation. Other scholars have designed an eccentric rotating galvanometer to make the rotation axis located on the surface of the reflecting mirror, but its versatility is poor. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a galvanometer rotation axis calibration method and system for rotary line laser scanning three-dimensional measurement. Its purpose is to achieve accurate calibration of the galvanometer rotation axis in rotary line laser scanning measurement, taking into account the non-coincidence between the galvanometer mirror surface and the rotation axis and the assembly error of the galvanometer.

[0005] To achieve the above objectives, according to a first aspect of the present invention, a method for calibrating the rotation axis of a galvanometer in a rotating line laser scanning three-dimensional measurement is proposed, comprising the following steps:

[0006] S1. The laser emitted by the line laser is directly incident on the stereo calibration plate. The incident laser stripes are collected by the auxiliary camera, and the incident laser plane in the measurement coordinate system of the auxiliary camera is obtained.

[0007] The laser emitted by the line laser is reflected onto the stereo calibration plate by a galvanometer. The galvanometer is rotated at multiple angles, and the reflected laser stripes are collected by the main camera. Thus, the reflected laser plane in the main camera measurement coordinate system corresponding to different galvanometer rotation angles is obtained.

[0008] S2. Based on the relative pose relationship between the auxiliary camera and the main camera, the incident laser plane in the measurement coordinate system of the auxiliary camera is transformed to the measurement coordinate system of the main camera.

[0009] S3. Based on the incident laser plane and reflected laser plane in the main camera measurement coordinate system, calculate the galvanometer mirror equation corresponding to different galvanometer rotation angles, and then determine the galvanometer rotation axis.

[0010] As a further preferred embodiment, step S3, based on the incident laser plane and the reflected laser plane in the main camera measurement coordinate system, calculates the galvanometer mirror equations corresponding to different galvanometer rotation angles, including:

[0011] The normal vector of the galvanometer surface is calculated using the following formula:

[0012] [(n i ×n rj ) n rj n i ] T ·n Mj =[0 cos(θ) j / 2) cos(θ j / 2)] T

[0013]

[0014] Where, n i Let n be the normal vector of the plane of incident laser light. rj Let n be the normal vector of the reflected laser plane corresponding to the j-th mirror rotation angle. Mj Let be the normal vector of the mirror surface corresponding to the j-th rotation angle of the galvanometer, and n be the total number of rotation angles of the galvanometer.

[0015] Then, take any point on the intersection line of the incident laser plane and the reflected laser plane, and combine it with the normal vector of the galvanometer surface to obtain the galvanometer surface equations corresponding to n different galvanometer rotation angles.

[0016] As a further preferred embodiment, step S3, determining the galvanometer rotation axis based on the galvanometer mirror surface equations corresponding to different galvanometer rotation angles, includes:

[0017] The direction vector n of the n galvanometer mirrors is obtained from the equations of the n galvanometer mirrors. mirror_j Then, the direction vector n of the galvanometer rotation axis can be calculated using the following formula. G :

[0018] Based on the equations of n galvanometer mirrors, the angle bisectors of n-1 adjacent galvanometer mirrors are obtained. The intersection of these angle bisectors is calculated, thus initially determining a point P on the galvanometer rotation axis. G For point P G By performing iterative optimization, point P is obtained. G Final value;

[0019] Combined with the mirror rotation axis direction vector n G and point P G The final value determines the rotation axis of the galvanometer.

[0020] As a further optimization, in step S3, for point P... G By performing iterative optimization, point P is obtained. G Final values, including:

[0021] Construct the following objective function F:

[0022]

[0023] in, Let P be the point G The mirror surface corresponding to the j-th rotation angle of the galvanometer The distance;

[0024] To initially determine a point P on the rotation axis of the galvanometer G Using this as the initial value, and based on the objective function, the LM method is used for iterative solution to obtain point P. G Final value.

[0025] As a further preferred embodiment, the three-dimensional calibration plate includes two hinged planar checkerboard calibration plates, namely a left checkerboard and a right checkerboard, the included angle of which is adjustable.

[0026] As a further preferred embodiment, step S2, the method for determining the relative pose relationship between the auxiliary camera and the main camera includes:

[0027] Adjust the position of the stereo calibration board so that the main camera can capture the entire stereo calibration board. Calculate the relative pose relationships between the main camera and the left and right checkerboard squares using the PnP method. This allows us to determine the relative poses of the left and right chessboard squares.

[0028] The position of the stereo calibration plate was readjusted so that the main camera could capture images of the left chessboard square, while the auxiliary camera could capture images of the right chessboard square. The relative pose relationships between the main camera and the left chessboard square, and between the auxiliary camera and the right chessboard square, were calculated using the PnP method. The relative pose relationship between the auxiliary camera and the main camera

[0029] As a further preferred option, step S1 specifically includes:

[0030] The laser emitted by the line laser is directly incident on the stereo calibration plate. The stereo calibration plate is moved, and the incident laser stripes corresponding to different positions of the stereo calibration plate are collected. Then, the incident laser plane in the auxiliary camera measurement coordinate system is obtained by fitting.

[0031] The laser emitted by the line laser is reflected onto the stereo calibration plate by a galvanometer. The galvanometer is controlled to rotate at multiple angles. For any rotation angle of the galvanometer: the stereo calibration plate is moved, and the reflected laser stripes corresponding to different positions of the stereo calibration plate are collected. Then, the reflected laser plane in the main camera measurement coordinate system corresponding to the rotation angle of the galvanometer is fitted to obtain the reflected laser plane.

[0032] As a further preferred embodiment, step S1, the method for obtaining the laser plane by fitting laser stripes, is as follows:

[0033] Based on the principle of cross-ratio invariance, the three-dimensional information of the laser stripe points in the corresponding camera measurement coordinate system is calculated by using the laser stripe image information and the checkerboard corner point information on the stereo calibration plate. Then, the laser plane is obtained by fitting the laser stripe points.

[0034] According to a second aspect of the present invention, a galvanometer axis calibration system for rotary line laser scanning three-dimensional measurement is provided, comprising a processor for performing the above-described galvanometer axis calibration method for rotary line laser scanning three-dimensional measurement.

[0035] According to a third aspect of the present invention, a computer-readable storage medium is provided having a computer program stored thereon, characterized in that, when the computer program is executed by a processor, it implements the above-described method for galvanometer axis calibration in rotary line laser scanning three-dimensional measurement.

[0036] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0037] 1. This invention takes into account the structural characteristics of the galvanometer itself not coinciding with the rotation axis, as well as the assembly problem of the relative positional relationship between the incident laser plane and the galvanometer. By introducing a three-dimensional calibration plate and an auxiliary camera to calibrate the galvanometer rotation axis, calibration can be performed quickly without changing the original rotating scanner structure. It can also compensate for the systematic errors of the line laser incident position installation error and the galvanometer mirror offset relative to the rotation axis, thereby improving the calibration accuracy of the galvanometer rotation axis during rotating line laser scanning measurement.

[0038] 2. This invention can be applied to the incident laser plane emitted from a laser emitter being projected onto a mirror surface in any orientation, without strictly ensuring that the rotation axis of the laser emitter and the galvanometer are coincident. The calibration method does not use ideal conditions as a priori conditions for axis calibration, making it more versatile.

[0039] 3. This invention establishes the geometric relationship between the incident laser plane, the reflected laser plane, the galvanometer mirror surface, and the galvanometer rotation axis. It introduces the concept of an envelope cylinder and then uses the angle bisector to calculate the direction vector and specific position of the galvanometer rotation axis. This allows for precise calibration of the galvanometer's position in the camera coordinate system and compensation for the offset of the galvanometer mirror surface relative to the rotation axis. Attached Figure Description

[0040] Figure 1 This is a flowchart of the galvanometer axis calibration method for rotary line laser scanning three-dimensional measurement provided by the present invention;

[0041] Figure 2 This is a schematic diagram of the measurement system provided by the present invention;

[0042] Figure 3 This is a schematic diagram of the measurement coordinate system provided by the present invention;

[0043] Figure 4 This is a schematic diagram of the three-dimensional calibration plate structure provided by the present invention;

[0044] Figure 5 This is a schematic diagram of the calibration principle of a point on the rotating shaft of the galvanometer provided by the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0046] This invention provides a method for calibrating the galvanometer axis in a rotating line laser scanning three-dimensional measurement system, such as... Figure 1 As shown, it includes the following steps:

[0047] First, a measurement system is pre-built, which includes a line laser self-scanning system and an auxiliary calibration device. For example... Figure 2 As shown, the line laser self-scanning system includes a main camera, a galvanometer, and a line laser, while the calibration device includes an auxiliary camera and a stereo calibration plate.

[0048] The main camera should be adjusted to a position that can capture the plane reflecting the laser, and the auxiliary camera should be adjusted to a position that can capture the plane incident on the laser. For example... Figure 4As shown, the stereo calibration plate consists of two planar checkerboard calibration plates connected by a hinge. The angle between the two planar checkerboard calibration plates (i.e., the left checkerboard and the right checkerboard) is adjustable, so it should be adjusted until the complete calibration plate appears in the field of view of both the main camera and the auxiliary camera.

[0049] Then, a measurement coordinate system is established, such as Figure 3 As shown, the camera measurement coordinate system is set to {C}, where the main camera measurement coordinate system is set to {C1}, the auxiliary camera measurement coordinate system is set to {C2}, and the galvanometer measurement coordinate system is set to {G}. For the stereo calibration plate, a local world coordinate system {W1} is established on the left checkerboard grid, and a local world coordinate system {W2} is established on the right checkerboard grid.

[0050] Based on the above measurement system, the galvanometer axis is calibrated:

[0051] S1. Perform laser plane calibration: including incident laser plane pose calibration and reflected laser plane pose calibration;

[0052] The laser emitted by the line laser is directly incident on the stereo calibration plate. The incident laser stripes are collected by an auxiliary camera, and the plane pose of the incident laser in the measurement coordinate system of the auxiliary camera is obtained.

[0053] Keeping the line laser in the same position, install a galvanometer. The laser emitted by the line laser is reflected by the galvanometer onto the stereo calibration plate. Control the galvanometer to rotate at multiple angles, and collect the reflected laser stripes through the main camera. Then, obtain the reflected laser plane pose in the main camera measurement coordinate system corresponding to different galvanometer rotation angles.

[0054] Specifically, by moving the checkerboard, laser stripes are obtained at multiple positions on the corresponding laser plane. Then, using the cross-ratio invariance principle, the two-dimensional image information of the laser stripes and the two-dimensional and three-dimensional information of the checkerboard corner points are used to calculate the three-dimensional information of the laser stripe points in the camera coordinate system {C}. Finally, the laser plane is fitted from the laser stripe points to determine the spatial pose of the laser plane in the camera coordinate system {C}.

[0055] S2. Based on the stereo calibration plate, determine the relative pose relationship between the auxiliary camera and the main camera, and then transform the incident laser plane in the measurement coordinate system of the auxiliary camera to the measurement coordinate system of the main camera, so that the incident laser plane and the reflected laser plane are unified in the measurement coordinate system of the main camera.

[0056] Furthermore, based on the stereo calibration plate, the relative pose relationship between the auxiliary camera and the main camera is determined, including:

[0057] The position of the stereo calibration plate was adjusted so that the main camera could completely capture the left and right chessboard squares on it. The relative pose relationship between the main camera and the left and right chessboard squares was calculated using the PnP method. This determines the relative positions of the left and right chessboard squares.

[0058] Then, the position of the stereo calibration plate was moved again so that the main camera could capture the left chessboard squares and the auxiliary camera could simultaneously capture the right chessboard squares, and the calculations were performed.

[0059] Obtain the pose relationship between the main camera and the auxiliary camera:

[0060]

[0061] Specifically, using Transform the incident laser plane to the main camera's measurement coordinate system {C1}:

[0062]

[0063] in, n is the normal vector of the incident laser plane, r is a point on the incident laser plane, and P input This is a homogeneous description of the plane of incident laser light.

[0064] S3. Based on the incident laser plane and reflected laser plane in the main camera measurement coordinate system, calculate the galvanometer mirror equation corresponding to different galvanometer rotation angles, and then determine the galvanometer rotation axis.

[0065] Furthermore, the incident laser plane is known. With the plane of reflection of the laser Solve the equation of the mirror

[0066] The equation AX = b can be constructed:

[0067] [(n i ×n rj ) n rj n i ] T ·n Mj =[0 cos(θ) j / 2) cos(θ j / 2)] T (3)

[0068]

[0069] Where, n i Let n be the normal vector of the plane of incident laser light. rj The normal vector of the reflected laser plane corresponding to the rotation angle of the j-th galvanometer (by...) (Confirmed); n Mj Let be the normal vector of the mirror surface corresponding to the j-th rotation angle of the mirror.

[0070] A point p on the mirror surface can be any point on the line of intersection between the incident laser plane and the reflected laser plane. j (x,y,z), and then combined with the normal vector of the galvanometer surface, we obtain the galvanometer surface equations corresponding to n different galvanometer rotation angles.

[0071] Furthermore, the rotation axis of the galvanometer is determined by the rotation axis direction vector n. G (nx G ,ny G ,nz G ) and a point P on the axis of rotation G (x G ,y G ,z G )definition;

[0072] Determine the axis of rotation direction vector: based on the mirror equation Obtain the direction vector n of the galvanometer mirror surface mirror_j Then, the direction vector n of the galvanometer rotation axis is calculated. G (nx G ,ny G ,nz G ):

[0073]

[0074] Determine a point on the axis of rotation: such as Figure 5 As shown, m is the distance from the reflecting surface of the galvanometer to the axis of rotation. The actual model of the galvanometer rotation is that the mirror rotates around the central axis with an offset distance m. Therefore, multiple mirrors can form a cylindrical surface with the axis of rotation as the axis and a radius of m. According to the geometric relationship, it can be deduced that the central axis of rotation of the galvanometer lies on the angle bisector between the mirrors.

[0075] Therefore, n-1 sets of angle bisectors can be calculated based on n sets of mirror equations. Then, the intersection of the angle bisectors can be obtained using formula (6), which is a point P on the axis of rotation. G (x G ,y G ,z G ):

[0076]

[0077] Among them, A j B j C j D j Angle Bisector The coefficient.

[0078] Further analysis of point P G (x G,y G ,z G Optimize:

[0079] If point P G (x G y G z G If the position calculation is correct, then point P... G (x G y G z G The distances to all mirror equations should be equal, therefore the objective function is constructed as follows:

[0080]

[0081] in, Let P be the point G To the mirror plane The distance formula is:

[0082]

[0083] Based on the objective function, P is obtained through formula (6). G (x G y G z G Using ) as the initial value, the LM method is used to evaluate point P. G (x G y G z G The solution is obtained by iterative solving, and point P is obtained. G Final value.

[0084] Based on the determined rotation axis direction vector and a point on the rotation axis, the pose of the galvanometer rotation axis in the main camera measurement coordinate system is accurately calibrated.

[0085] This can compensate for the errors caused by the installation of the galvanometer and line laser during measurement. The installation error of the galvanometer and line laser refers to the fact that, in an ideal situation, the incident laser plane is completely coincident with the rotation axis of the galvanometer. In reality, the line laser emitted by the laser does not coincide with the rotation axis of the galvanometer, and may intersect, be parallel, or be out of plane, resulting in installation errors compared to the ideal situation.

[0086] In summary, this invention takes into account the structural design of the galvanometer itself not coinciding with the axis of rotation, as well as the assembly problem of the relative positional relationship between the incident laser plane and the galvanometer. It does not require the incident laser plane to coincide with, be parallel to, intersect with, or be in a different plane from the galvanometer's axis of rotation. By introducing an auxiliary camera, a calibration model that better reflects the actual assembly situation can be established, thereby improving the overall calibration accuracy of the measurement system and making the method more versatile.

[0087] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A mirror rotation axis calibration method for a rotary line laser scanning three-dimensional measurement, characterized in that, Includes the following steps: S1. The laser emitted by the line laser is directly incident on the stereo calibration plate. The incident laser stripes are collected by the auxiliary camera, and the incident laser plane in the measurement coordinate system of the auxiliary camera is obtained. The laser emitted by the line laser is reflected onto the stereo calibration plate by a galvanometer. The galvanometer is rotated at multiple angles, and the reflected laser stripes are collected by the main camera. Thus, the reflected laser plane in the main camera measurement coordinate system corresponding to different galvanometer rotation angles is obtained. S2. Based on the relative pose relationship between the auxiliary camera and the main camera, the incident laser plane in the measurement coordinate system of the auxiliary camera is transformed to the measurement coordinate system of the main camera. S3. Based on the incident laser plane and reflected laser plane in the main camera measurement coordinate system, calculate the galvanometer mirror equations corresponding to different galvanometer rotation angles, and then determine the galvanometer rotation axis; including: The normal vector of the galvanometer surface is calculated using the following formula: wherein, is a normal vector of the incident laser plane, is a normal vector of the reflected laser plane corresponding to the rotation angle of the first mirror, is a normal vector of the reflected laser plane corresponding to the rotation angle of the second mirror, n is a normal vector of the mirror surface corresponding to the rotation angle of the second mirror, and Then, taking any point on the intersection line of the incident laser plane and the reflected laser plane, and combining it with the normal vector of the galvanometer mirror, we obtain... n The equations of the galvanometer mirror surface corresponding to different galvanometer rotation angles; Based on the galvanometer mirror surface equations corresponding to different galvanometer rotation angles, determine the galvanometer rotation axis, including: according to n The equations for the galvanometer mirrors are obtained. n The direction vector of each galvanometer mirror surface The direction vector of the galvanometer rotation axis can then be calculated using the following formula. : ; according to n The equations for the galvanometer mirrors are obtained. n -1. Calculate the angle bisectors of adjacent galvanometer mirrors, and thus preliminarily determine a point on the galvanometer's rotation axis. Point Iterative optimization is performed to obtain the point. Final value; Combined with the rotation axis direction vector of the galvanometer and points The final value determines the rotation axis of the galvanometer.

2. The galvanometer axis calibration method for rotary line laser scanning three-dimensional measurement as described in claim 1, characterized in that, Step S3, point Iterative optimization is performed to obtain the point. Final values, including: Construct the following objective function F : in, For point To the The galvanometer mirror surface corresponding to each galvanometer rotation angle The distance; To preliminarily determine a point on the rotation axis of the galvanometer Using the objective function as the initial value, the LM method is used iteratively to obtain the point. Final value.

3. The galvanometer axis calibration method for rotary line laser scanning three-dimensional measurement as described in claim 1, characterized in that, The three-dimensional calibration plate includes two hinged planar checkerboard calibration plates, namely the left checkerboard and the right checkerboard, and the included angle between the left checkerboard and the right checkerboard is adjustable.

4. The galvanometer axis calibration method for rotary line laser scanning three-dimensional measurement as described in claim 3, characterized in that, Step S2, the method for determining the relative pose relationship between the auxiliary camera and the main camera includes: Adjust the position of the stereo calibration board so that the main camera can capture the entire stereo calibration board. Calculate the relative pose relationships between the main camera and the left and right checkerboard squares using the PnP method. , This allows us to determine the relative poses of the left and right chessboard squares. ; The position of the stereo calibration plate was readjusted so that the main camera could capture images of the left chessboard square, while the auxiliary camera could capture images of the right chessboard square. The relative pose relationships between the main camera and the left chessboard square, and between the auxiliary camera and the right chessboard square, were calculated using the PnP method. , The relative pose relationship between the auxiliary camera and the main camera. .

5. The galvanometer axis calibration method for rotary line laser scanning three-dimensional measurement as described in any one of claims 1-4, characterized in that, Step S1 specifically includes: The laser emitted by the line laser is directly incident on the stereo calibration plate. The stereo calibration plate is moved, and the incident laser stripes corresponding to different positions of the stereo calibration plate are collected. Then, the incident laser plane in the auxiliary camera measurement coordinate system is obtained by fitting. The laser emitted by the line laser is reflected onto the stereo calibration plate by a galvanometer. The galvanometer is controlled to rotate at multiple angles. For any rotation angle of the galvanometer: the stereo calibration plate is moved, and the reflected laser stripes corresponding to different positions of the stereo calibration plate are collected. Then, the reflected laser plane in the main camera measurement coordinate system corresponding to the rotation angle of the galvanometer is fitted to obtain the reflected laser plane.

6. The galvanometer axis calibration method for rotary line laser scanning three-dimensional measurement as described in claim 5, characterized in that, Step S1, the method for obtaining the laser plane by fitting laser stripes is as follows: Based on the principle of cross-ratio invariance, the three-dimensional information of the laser stripe points in the corresponding camera measurement coordinate system is calculated by using the laser stripe image information and the checkerboard corner point information on the stereo calibration plate. Then, the laser plane is obtained by fitting the laser stripe points.

7. A galvanometer axis calibration system for rotary line laser scanning three-dimensional measurement, characterized in that, Includes a processor for performing a galvanometer axis calibration method for rotary line laser scanning three-dimensional measurement as described in any one of claims 1-6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the galvanometer axis calibration method for rotary line laser scanning three-dimensional measurement as described in any one of claims 1-6.

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