A laser vision-guided robot automatic welding hand-eye calibration method

Abstract

The present application relates to visual robot automatic welding technical field, specifically a kind of laser visual guidance robot automatic welding hand-eye calibration method, including steps (1) design a three-dimensional calibration board with three calibration points, determine welding model;Step (2) according to the calibration point and the welding model, the calibration of the transformation matrix between the calibration board coordinate system and the robot base coordinate system is carried out;Step (3) moves the robot to collect the linear laser calibration line projected on the three-dimensional calibration board by linear laser sensor, obtains calibration feature points, completes hand-eye calibration.This method is simple in operation, and calibration precision is higher, is suitable for on-site rapid calibration, fully meets the precision requirement of automatic guidance welding.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of visual robot automatic welding, and particularly relates to a laser visual guidance robot automatic welding hand-eye calibration method. BACKGROUND

[0002] With the development of industrial automation and intelligence, the demand for visual guidance robot automatic welding is increasing. A visual sensor is installed at the end of a manipulator, and three-dimensional trajectory information of a weld is acquired through the visual sensor to guide the manipulator to complete the entire welding process. The three-dimensional information acquired by the sensor is in the visual sensor coordinate system, so it is necessary to establish the transformation relationship between the visual sensor coordinate system and the manipulator coordinate system to convert the three-dimensional information of the sensor into trajectory information under the manipulator. The process of establishing the transformation relationship between the sensor coordinate system and the manipulator coordinate system is called hand-eye calibration, and the quality of the hand-eye calibration result directly affects the accuracy of the final guided welding.

[0003] A visual guidance robot automatic welding system mainly includes a line laser three-dimensional visual sensor, a six-axis manipulator, a welding torch, and a motion controller. Installing the visual sensor at the end of the manipulator belongs to the eye-in-hand hand-eye calibration problem. A classical calibration method solves the matrix equation set AX=XB through a quaternion, where A is the motion matrix of the manipulator, B is the motion matrix of the sensor, and X is the transformation matrix to be calibrated. This calibration method requires that the two motions of the manipulator keep the rotation axes of the end non-parallel during the calibration process, the calibration process is complicated to operate, the calibration accuracy is unstable, and it is not suitable for on-site rapid calibration.

[0004] Therefore, there is an urgent need for a technology to solve this problem. SUMMARY

[0005] The present application aims to overcome the problems of the prior art and provides a laser visual guidance robot automatic welding hand-eye calibration method. First, a special three-dimensional calibration board is designed according to the imaging characteristics of the line laser sensor, and the relationship between the manipulator coordinate system and the calibration board coordinate system can be quickly established through three calibration points on the calibration board. Then, the line laser calibration line on the calibration board is collected by adjusting the posture of the manipulator. Finally, the hand-eye calibration between the manipulator and the line laser sensor is completed according to the high-precision calibration line and the calibration feature points obtained.

[0006] The above-mentioned purpose is achieved by the following technical solutions:

[0007] A laser visual guidance robot automatic welding hand-eye calibration method, comprising:

[0008] Step (1) design a three-dimensional calibration board with three calibration points, and determine a welding model;

[0009] Step (2) calibrates the transformation matrix between the calibration plate coordinate system and the robot base coordinate system according to the calibration points and the welding model;

[0010] Step (3) moves the robot to collect the line laser calibration line projected on the three-dimensional calibration plate through the line laser sensor to obtain the calibration feature points and complete the hand-eye calibration.

[0011] Further, the welding model in step (1) is:

[0012] The robot base coordinate system is set as O b -x b y b z b The robot end coordinate system is set as O e -x e y e z e The calibration plate coordinate system is set as O c -x c y c z c The line laser sensor coordinate system is set as O l -x l y l z l

[0013] The conversion matrix of the robot end coordinate system to the robot base coordinate system is which can be obtained by reading the controller of the robot;

[0014] The conversion matrix of the calibration plate coordinate system to the robot base coordinate system is

[0015] The conversion matrix of the line laser sensor coordinate system to the robot end coordinate system is

[0016] Let P be a point on the weld, and its coordinate in the laser sensor is p l The coordinate of P in the robot base coordinate system is p b

[0017]

[0018] Further, the step (2) is specifically:

[0019] The coordinates of the three calibration points in the calibration plate coordinate system are set as The end point of the welding torch is respectively aligned with the calibration points to obtain the coordinates of the calibration points in the base coordinate system

[0020] Calibration​​ Define coordinate system O t -x t y t z t The origin of this coordinate system is located at the calibration point. If the orientation of the coordinate system is the same as that of the base coordinate system, then the calibration point is at O. t -x t y t z t The coordinates in the middle are:

[0021]

[0022] Robotic arm base coordinate system O b -x b y b z b coordinate system O of the calibration plate t -x t y t z t The displacement relationship between them is:

[0023]

[0024] Calibration plate coordinate system O t -x t y t z t coordinate system O of the calibration plate C -x c y c z c The rotational relationship between them is:

[0025]

[0026] Therefore:

[0027]

[0028]

[0029] From equation (6), we can obtain the parametric equations for the first column r1 and the second column r2 of the rotation matrix R = [r1 r2 r3]:

[0030]

[0031] set up:

[0032]

[0033] r=[r1, r2, r4, r5, r6, r7] T ,

[0034] There are:

[0035]

[0036] According to the orthogonality of the rotation matrix and the vector, r3 can be obtained:

[0037]

[0038] After obtaining , formula (5) is obtained

[0039] Further, the step (3) is specifically:

[0040] Adjust the pose of the manipulator to align the line laser with the calibration line on the calibration board, and then transform the pose of the manipulator to collect the laser calibration line. The relationship between the collected laser calibration line and the calibration board is collected.

[0041] Set as the two endpoints of the laser line, and the coordinates of the two endpoints in the laser sensor coordinate system are obtained directly by the sensor. The distance between the two endpoints is L:

[0042]

[0043] Then the coordinates of the endpoints in the calibration board coordinate system are

[0044]

[0045] Set the current pose of the manipulator as According to , the coordinates of the endpoints in the end coordinate system can be obtained

[0046]

[0047] Repeat the calibration line collection process n times to obtain and Set the hand-eye relationship as Then we have:

[0048]

[0049] According to the Kabsch algorithm, the initial values R0 and T0 of the rotation matrix R and the displacement vector T between the corresponding point sets and are calculated. Finally, the precise values of R and T are obtained by minimizing the error as follows through the LM algorithm, and the final

[0050]

[0051] Advantages

[0052] The laser vision guided robot automatic welding hand-eye calibration method provided by the application designs a special three-dimensional calibration plate according to the characteristics of the line laser sensor, first calibrates the relationship between the calibration plate and the robot, then modulates the line laser through the calibration plate, and finally collects the calibration feature points for hand-eye calibration. The method is simple to operate, has high calibration precision, is suitable for on-site rapid calibration, and fully meets the precision requirements of automatic guided welding. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 A visual guided automatic welding system model schematic diagram of the laser vision guided robot automatic welding hand-eye calibration method described in the application;

[0054] Figure 2 A three-dimensional calibration plate and a calibration plate plane parameter schematic diagram of the laser vision guided robot automatic welding hand-eye calibration method described in the application;

[0055] Figure 3 A hand-eye calibration operation schematic diagram of the laser vision guided robot automatic welding hand-eye calibration method described in the application;

[0056] Figure 4 A line laser and a calibration feature point corresponding image of the laser vision guided robot automatic welding hand-eye calibration method described in the application;

[0057] Figure 5 A coordinate system coordinate table corresponding to three calibration points of the laser vision guided robot automatic welding hand-eye calibration method described in the application;

[0058] Figure 6 A feature end point coordinate and a robot posture table collected by three calibration lines of the laser vision guided robot automatic welding hand-eye calibration method described in the application. DETAILED DESCRIPTION

[0059] The application will be further described in detail below according to the drawings and embodiments. The described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0060] A laser vision guided robot automatic welding hand-eye calibration method, comprising the following steps:

[0061] Step (1) design a three-dimensional calibration plate with three calibration points, and determine a welding model;

[0062] Step (2) calibrates the transformation matrix between the calibration plate coordinate system and the manipulator base coordinate system according to the calibration point and the welding model;

[0063] Step (3) moves the manipulator to collect the linear laser calibration line projected on the three-dimensional calibration plate by the linear laser sensor to obtain the calibration feature point and complete the hand-eye calibration.

[0064] As shown in Figure 2 , the three-dimensional calibration plate designed in the scheme is in a trapezoidal shape, and a horizontal isosceles triangle calibration plate is arranged on the top slope as a calibration surface.

[0065] As shown in Figure 1 , the welding model in step (1) is:

[0066] The manipulator base coordinate system is set as O b -x b y b z b , the manipulator end coordinate system is set as O e -x e y e z e , the calibration plate coordinate system is set as O c -x c y c z c , and the linear laser sensor coordinate system is set as O l -x l y l z l , then:

[0067] The conversion matrix of the manipulator end coordinate system to the manipulator base coordinate system is which can be obtained by reading the controller of the manipulator;

[0068] The conversion matrix of the calibration plate coordinate system to the manipulator base coordinate system is

[0069] The conversion matrix of the linear laser sensor coordinate system to the manipulator end coordinate system is Since the linear laser sensor is bound to the end of the manipulator, T l e is fixed and unchanged, and the hand-eye calibration is to determine the value of .

[0070] Let P be a point on the weld, and its coordinates in the laser sensor are p l , then the coordinates p b of P in the manipulator base coordinate system are:

[0071]

[0072] As the optimization of step (2), the step (2) is specifically:

[0073] As shown in the figure, set the coordinates of three calibration points in the calibration plate coordinate system respectively as Align the end point of the welding gun with the calibration points respectively to obtain the coordinates of the calibration points in the base coordinate system

[0074] Calibration Define the coordinate system O t -x t y t z t , the origin of which is located at the calibration point The direction of the coordinate system is consistent with the direction of the base coordinate system, so the coordinates of the calibration point in O t -x t y t z t are:

[0075]

[0076] The displacement relationship between the base coordinate system O b -x b y b z b and the calibration plate coordinate system O t -x t y t z t is:

[0077]

[0078] The rotation relationship between the calibration plate coordinate system O t -x t y t z t and the calibration plate coordinate system O C -x c y c z c is:

[0079]

[0080] Therefore:

[0081]

[0082]

[0083] From equation (6), the parametric equation about the first column r1 and the second column r2 of the rotation matrix R = [r1 r2 r3] can be obtained:

[0084]

[0085] Let

[0086]

[0087] r = [r1, r2, r4, r5, r6, r7] T ,

[0088] Let

[0089]

[0090] According to the orthogonality of the rotation matrix column vectors, we have r3:

[0091]

[0092] After obtaining , we have

[0093] As shown in Figure 3 , as a step (3) of the optimization, the step (3) is specifically:

[0094] Adjust the pose of the manipulator to align the line laser with the calibration line on the calibration board, as shown in Figure 3 (a);

[0095] Then, adjust the pose of the manipulator to collect the laser calibration line, as shown in Figure 3 (b).

[0096] The relationship between the collected laser calibration line and the calibration board is shown in Figure 3 (c),

[0097] are the two endpoints of the laser line, whose coordinates in the laser coordinate system are obtained directly by the sensor, and the distance between the two endpoints is

[0098]

[0099] Then the coordinates of the endpoints in the calibration board coordinate system are

[0100]

[0101]

[0102] Let the current pose of the manipulator be According to the obtained in the last section, the coordinates of the endpoints in the end coordinate system are

[0103]

[0104] Repeat the line calibration process n times, and the following can be obtained And Let the hand-eye relationship be Then:

[0105]

[0106] According to the Kabsch algorithm, the initial values R0 and T0 of the rotation matrix R and the displacement vector T between the corresponding point sets And are calculated, and finally the precise values of R and T are obtained by minimizing the error through the LM algorithm, and finally

[0107]

[0108] As shown in Figure 5 , it is a coordinate system coordinate table corresponding to the calibration points, which gives the coordinates of the calibration points p i , i = 1, 2, 3 in the calibration plate coordinate system and its coordinates in the base coordinate system, which can be obtained through the above formulas (5) and (7):

[0109]

[0110] As shown in Figure 4 , it is a line laser image and its feature endpoint image collected when hand-eye calibration is performed, Figure 6 is a table of feature endpoint coordinates and robot pose collected by three calibration lines, which gives the feature endpoint laser coordinates and the corresponding robot end pose parameters obtained after three line laser calibration line collection, and the hand-eye calibration parameters are obtained according to the above hand-eye calibration method:

[0111]

[0112] The above only describes the embodiments of the present application and is not used to limit the present application. For those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A laser vision-guided robot automatic welding hand-eye calibration method, characterized in that, include: Step (1) Design a three-dimensional calibration plate with three calibration points. The three-dimensional calibration plate is trapezoidal in shape, and a horizontal isosceles triangular calibration surface is set on the top sloping surface. The three calibration points are located on the isosceles triangular calibration surface. Determine the welding model, which is: Set the robot's base coordinate system as Set the coordinate system of the robot arm's end effector as follows: Set the calibration plate coordinate system as follows: The coordinate system of the line laser sensor is set as follows: ,but: The transformation matrix from the end effector coordinate system to the base coordinate system of the robot is: This can be obtained by reading the controller of the robotic arm; The transformation matrix from the calibration plate coordinate system to the robot's base coordinate system is: ; The transformation matrix from the line laser sensor coordinate system to the robot end effector coordinate system is: ; Let P be a point on the weld, and its coordinates in the laser sensor be... Then the coordinates of P in the robot's base coordinate system have: （1）； Step (2) Based on the calibration points and the welding model, calibrate the transformation matrix between the calibration plate coordinate system and the robot's base coordinate system; specifically, set the coordinates of the three calibration points in the calibration plate coordinate system as follows: Align the tip of the welding torch with the calibration points to obtain the coordinates of the calibration points in the base coordinate system. ; Calibration Define coordinate system The origin of this coordinate system is located at the calibration point. If the direction of the coordinate system is the same as the direction of the base coordinate system, then the calibration point is in The coordinates in the middle are: （2） Robotic arm base coordinate system coordinate system with calibration plate The displacement relationship between them is: （3） Calibration plate coordinate system coordinate system with calibration plate The rotational relationship between them is: （4） Therefore, we have: (5) （6） From equation (6), we can obtain information about the rotation matrix. The first column Second column Parametric equations: （7） set up: , , ,have: , Based on the orthogonality of the column vectors of the rotation matrix, we can obtain : （8） In obtaining Then, from equation (5), we get ; Step (3) The mobile robotic arm acquires the line laser calibration lines projected onto the three-dimensional calibration plate using a line laser sensor, obtains the calibration feature points, and completes the hand-eye calibration; specifically: Adjust the robot's posture to align the line laser with the calibration line on the calibration plate, then change the robot's posture to collect the laser calibration line, and determine the relationship between the collected laser calibration line and the calibration plate. set up The two endpoints of the laser line are given, and their coordinates in the linear laser sensor coordinate system are obtained directly from the sensor. The distance between the two endpoints is L. （9） Then the coordinates of the endpoints in the calibration plate coordinate system : （10） Let the current posture of the robotic arm be... ,according to This allows us to obtain the coordinates of the endpoint in the end coordinate system. : （11） By repeating the calibration line acquisition process n times, we can obtain... and Let the hand-eye relationship be... , Then we have: (12) Calculate the corresponding point set using the Kabsch algorithm. and Initial values ​​of the rotation matrix R and the translation vector T between them and Finally, the accurate estimates of R and T are obtained by minimizing the following errors using the LM algorithm, resulting in the final estimate. ; （13）。

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