Method for calibrating an industrial robot tool coordinate system based on a laser scanner

Abstract

The application discloses a kind of industrial robot tool coordinate system calibration methods based on laser scanner, comprising the following steps: the end of robot A5 axis is parallel to base surface, keep the center position of flange unchanged, make the center of flange rotate around flange coordinate system X axis, Y axis, Z axis respectively, take 10 points in each rotating direction, collect the three-dimensional point cloud of target ball in each position, fit the ball center coordinates of each position, fit the fitting circle of each rotating direction according to ball center coordinates, determine the distance of target ball ball center from flange center in X axis, Y axis, Z axis direction according to fitting radius, move industrial robot, move to X axis, Y axis, Z axis positive direction, determine the relative position of target ball in flange coordinate system, input the coordinate position into robot control system, and robot automatically generates the tool coordinate system of target ball ball center.The present application is simple to operate, and has high calibration accuracy.

Description

TECHNICAL FIELD

[0001] The present application relates to a laser scanner-based industrial robot tool coordinate system calibration method, and relates to the field of industrial measurement. BACKGROUND

[0002] In industrial production, a tracking laser wireless three-dimensional scanner is used to scan a workpiece to be welded to obtain a high-precision three-dimensional point cloud model of the workpiece. The three-dimensional point cloud model is processed to obtain point cloud coordinates of a weld seam of the workpiece to be welded. The point cloud coordinates are converted into point position coordinates in an industrial robot coordinate system.

[0003] In the process, how to convert the point cloud coordinates into the point position coordinates in the industrial robot coordinate system requires using a target ball as an intermediate conversion target. Before this, the tool coordinates of the target ball in the industrial robot coordinate system need to be determined.

[0004] Therefore, how to accurately obtain the tool coordinates of the target ball in the industrial robot coordinate system is crucial to improving the accuracy of coordinate system conversion. SUMMARY

[0005] The present application aims to use a ball with a known radius, rotate the center of an end flange of an industrial robot around three axes of a flange coordinate system, fit the radius and center of a fitting circle obtained in each direction, solve the values of the coordinates of the center of the ball by solving a system of equations with the fitting circle radius, and move the target ball installed on the end flange of the industrial robot to two positions in space to obtain the positive directions of the X, Y, and Z axes of the coordinate system of the center of the ball.

[0006] The technical solutions for achieving the object of the present application are as follows:

[0007] A laser scanner-based industrial robot tool coordinate system calibration method first needs to determine the TCP point of the coordinate system of the center of a target ball in a flange coordinate system of an industrial robot. First, rotate the target ball installed at the end of the industrial robot around the center of the flange of the end of the industrial robot around the X, Y, and Z axes of the flange coordinate system and use a laser scanner to collect 10 points in each direction. The steps include the following:

[0008] (1) Place a laser tracker 3 meters in front of the body of the industrial robot and preheat it in advance;

[0009] (2) Fix a target ball connector and a target ball on the flange at the end of the body of the industrial robot;

[0010] (3) Adjust the A5 axis of the industrial robot to be parallel to the base surface, change the rotation angle of the A6 axis to 0°, and record the coordinate posture at this time as the initial pose P0;

[0011] Keep the flange coordinate unchanged, change the robot posture, operate the industrial robot to make its end rotate clockwise around the X axis direction of the flange coordinate system, gradually change its posture and record the three-dimensional point cloud of the current position, record 10 points, and number them as X1~X 10 ;

[0012] Repeat steps (2)~(3), operate the industrial robot to make its end rotate clockwise around the Y axis direction of the flange coordinate system, gradually change its posture and record the three-dimensional point cloud of the current position, record 10 points, and number them as Y1~Y 10 ;

[0013] Repeat steps (2)~(3), operate the industrial robot to make its end rotate clockwise around the Z axis direction of the flange coordinate system, gradually change its posture and record the three-dimensional point cloud of the current position, record 10 points, and number them as Z1~Z 10 .

[0014] Further, suppose that the radius of the circle fitted around the X axis of the flange coordinate system is R X , the radius of the circle fitted around the Y axis of the flange coordinate system is R Y , and the radius of the circle fitted around the Z axis of the flange coordinate system is R Z .

[0015] Further, according to the obtained fitting circle radius value, the equation set is solved to obtain the nominal value of the sphere center coordinates, including the following steps:

[0016] Suppose the sphere center coordinates of the target sphere are (X, Y, Z);

[0017] When the target sphere rotates around the X axis of the flange coordinate system, the projection of the sphere center of the target sphere on the Y axis and the Z axis to the sphere center is unchanged, then the square of the fitting circle radius value R X around the X axis of the flange coordinate system is equal to:

[0018] R x 2 = |Y| 2 + |Z| 2

[0019] When the target sphere rotates around the Y axis of the flange coordinate system, the projection of the sphere center of the target sphere on the X axis and the Z axis to the sphere center is unchanged, then the square of the fitting circle radius value R Y around the Y axis of the flange coordinate system is equal to:

[0020] Ry 2 =|X| 2 +|Z| 2

[0021] When the target sphere rotates around the Z-axis of the flange coordinate system, the distances from the projections of the target sphere's center onto the center of the sphere along the X and Y axes remain constant. Therefore, the radius R of the fitted circle around the Z-axis of the flange coordinate system is... Z The square of is equal to:

[0022] R z 2 =|X| 2 +|Y| 2

[0023] The final system of equations:

[0024]

[0025] Finally, the values ​​of X, Y, and Z are solved, thereby determining the TCP of the target ball;

[0026] Furthermore, the positive X, Y, and Z directions of the target ball tool coordinate system are the same as the positive directions of the flange end coordinate system. The industrial robot is moved two points along the X, Y, and Z axes, and the specific steps are as follows:

[0027] (1) Return the industrial robot to its initial posture P0, and move the industrial robot 100mm in the X-axis direction of the flange coordinate system. Record the reading X of the first point in the robot flange coordinate system. p1 After moving 100mm, record the second point X. p2 This allows us to determine the positive direction of the X-axis in the flange coordinate system, as well as the positive direction of the X-axis in the tool coordinate system of the target sphere. It also allows us to determine the sign of the TCP point on the target sphere.

[0028] (2) Repeat step (1) for the Y-axis to determine the positive direction of the tool coordinate Y-axis of the target ball;

[0029] (3) Repeat step (1) for the Z-axis to determine the positive direction of the Z-axis of the target ball's tool coordinates;

[0030] By inputting the TCP coordinates of the target ball into the robot control system, the tool coordinate system of the target ball's center can be obtained.

[0031] This invention has significant advantages over existing technologies:

[0032] 1. This invention is easy to operate and has high calibration accuracy. Attached Figure Description

[0033] Figure 1 This is a schematic diagram showing the target ball's center rotating around the Z-axis of the flange coordinate system.

[0034] Figure 2 Figure 1 is a schematic diagram of the target ball rotating around the Y axis of the flange coordinate system.

[0035] Figure 3 Figure 2 is a schematic diagram of the target ball rotating around the X axis of the flange coordinate system.

[0036] Figure 4 Figure 3 is a schematic diagram of the installation method of the target ball on the end flange of the industrial robot.

[0037] Figure 5 Figure 4 is a schematic diagram of the 10 collection points of the target ball in different positions in space.

[0038] Figure 6 Figure 5 is a schematic diagram of the fitting result of the center of the three-dimensional point cloud ball.

[0039] Figure 7 Figure 6 is a schematic diagram of the fitting circle result.

[0040] Table 1 is the center and radius of the fitting circle. DETAILED DESCRIPTION

[0041] The present application will be further described below in conjunction with the accompanying drawings

[0042] A method for obtaining the tool coordinates of the center of the target ball in the coordinate system of the industrial robot base by using a tracking laser wireless three-dimensional scanner, the method comprising: adjusting the A5 axis of the industrial robot to be parallel to the base surface, changing the rotation angle of the A6 axis to 0°, and recording the coordinate posture at this time as the initial pose P0;

[0043] A method for obtaining the tool coordinates of the center of the target ball in the coordinate system of the industrial robot base by using a tracking laser wireless three-dimensional scanner, the method comprising: keeping the flange coordinate unchanged, changing the robot pose, rotating the industrial robot clockwise around the X axis direction of the flange coordinate system, gradually changing the pose and recording the three-dimensional point cloud at the current position, recording 10 points, and numbering them as X1-X10. 10 ;

[0044] A method for obtaining the tool coordinates of the center of the target ball in the coordinate system of the industrial robot base by using a tracking laser wireless three-dimensional scanner, the method comprising: returning the industrial robot to the initial pose P0, changing the robot pose, rotating the industrial robot clockwise around the Y axis direction of the flange coordinate system, gradually changing the pose and recording the three-dimensional point cloud at the current position, recording 10 points, and numbering them as Y1-Y10. 10 ;

[0045] The method for obtaining the ball center tool coordinate of the target ball under the industrial robot base coordinate system by using the tracking laser wireless three-dimensional scanner, the method comprising: returning the industrial robot to the initial pose P0, changing the robot pose, rotating the industrial robot clockwise around the Y axis direction of the flange coordinate system, gradually changing the pose and recording the three-dimensional point cloud of the current position, recording 10 points, and numbering them as Y1-Y10. 10 ;

[0046] The method for obtaining the ball center tool coordinate of the target ball under the industrial robot base coordinate system by using the tracking laser wireless three-dimensional scanner, the method comprising: returning the industrial robot to the initial pose P0, changing the robot pose, rotating the industrial robot clockwise around the Y axis direction of the flange coordinate system, gradually changing the pose and recording the three-dimensional point cloud of the current position, recording 10 points, and numbering them as Y1-Y10. 10 ;

[0047] The three-dimensional point cloud obtained by each point in each direction is fitted with the ball center fitting algorithm to obtain the ball center coordinates of each point in each direction, and a fitting circle is fitted according to the ball center coordinates to obtain the fitting circle radii of each direction, wherein the fitting circle radius around the X axis of the flange coordinate system is R X , the fitting circle radius around the Y axis of the flange coordinate system is R Y , and the fitting circle radius around the Z axis of the flange coordinate system is R Z . The ball center coordinates of the target ball are (X, Y, Z), and the square of the fitting circle radius value R X around the X axis of the flange coordinate system is equal to:

[0048] R x 2 = |Y| 2 + |Z| 2

[0049] The square of the fitting circle radius value R X around the X axis of the flange coordinate system is equal to:

[0050] R y 2 = |X| 2 + |Z| 2

[0051] The square of the fitting circle radius value R Z around the Z axis of the flange coordinate system is equal to:

[0052] R z 2 = |X| 2 + |Y| 2

[0053] The final equation set is:

[0054]

[0055] Finally, the values of X, Y, and Z are solved, and the values of X, Y, and Z are positive and negative, and the positive values are taken. Then, the positive and negative of x, y, and z are determined.

[0056] The target ball is placed according to Figure 4 The target ball is placed according to

[0057] The handle of the industrial robot is operated, and the C+, B+, and Z+ buttons are pressed to make the industrial robot rotate around the X, Y, and Z axes of the coordinate system, as shown in Figure 5 The tracking laser three-dimensional scanner is used to collect 10 points in each direction to obtain the three-dimensional point cloud of the target ball at the position.

[0058] As shown in Figure 6 The center of the sphere is fitted for the three-dimensional point cloud data of each position, so as to obtain the center coordinates of the three-dimensional point cloud and the radius of the fitted circle, as shown in Table 1.

[0059] The position of the center of the target ball in the flange coordinate is (X, Y, Z), and finally the equation set is as follows:

[0060]

[0061] It can be converted to:

[0062]

[0063] The matrix is inverted, and finally the values of X, Y, and Z can be solved, X = 1578.49, Y = 94.63, and Z = 105.04

[0064] The positive and negative of each axis of the industrial robot are determined, and finally X = 578.49, Y = -94.63, and Z = 105.04 are obtained. The TCP point of the target ball is input into the industrial robot.

[0065]

[0066] Table 1

Claims

1. A method for calibrating a tool coordinate system of an industrial robot based on a laser scanner, characterized by: First, the TCP point of the target ball coordinate system in the flange coordinate system of the industrial robot is determined. First, the target ball installed at the end of the industrial robot is rotated around the flange center of the industrial robot end around the X, Y, Z axes of the flange coordinate system, and 10 points are collected in each direction using a laser scanner, including the following steps: (1) Place the laser tracker 3 meters in front of the industrial robot body and preheat in advance; (2) Fix the target ball connector and the target ball on the flange at the end of the industrial robot body; (3) Adjust the A5 axis of the industrial robot to be parallel to the base surface, change the rotation angle of the A6 axis to 0°, and record the coordinate posture at this time as the initial pose P0; (4) Keep the flange coordinate unchanged, change the robot pose, operate the industrial robot to make its end around the X axis direction of the flange coordinate system clockwise rotation, gradually change its pose and record the current position of the three-dimensional point cloud, record 10 points, and number them as X1~X10. 10 ; (5) Repeat steps (2)-(3), operate the industrial robot to rotate its end around the Y-axis direction of the flange coordinate system clockwise, gradually change its posture and record the three-dimensional point cloud of the current position, record 10 points, and number them as Y1-Y10. 10 ; (6) Repeat steps (2)-(3), operate the industrial robot to rotate its end around the Z-axis direction of the flange coordinate system clockwise, gradually change its posture and record the three-dimensional point cloud of the current position, record 10 points, and number them as Z1-Z10. 10 ; (7) Set around the flange coordinate system X axis fitting circle radius R X , around the flange coordinate system Y axis fitting circle radius R Y , around the flange coordinate system Z axis fitting circle radius R Z , the 10 points of each direction collected three-dimensional point cloud using geomagic studio software fitted each point in the tracking laser scanner coordinate system under the spherical coordinates, according to the spherical coordinates fitting circle, obtain the fitting circle radius value of each direction; (8) Obtain the nominal value of the ball center coordinates according to the obtained fitting circle radius value and the equation set to determine the TCP of the target ball.

2. The laser scanner based industrial robot tool frame calibration method according to claim 1, characterized in that: According to the obtained fitting circle radius value and the equation set to obtain the nominal value of the ball center coordinates, including the following steps: (1) Let the ball center coordinates of the target ball be (X, Y, Z); (2) When the target ball rotates around the X-axis of the flange coordinate system, the distance from the projection of the center of the target ball on the Y-axis and the Z-axis to the center of the target ball is constant, then the square of the fitting circle radius value R of the X-axis of the flange coordinate system is equal to: X ​ ； (3) When the target ball rotates around the Y axis of the flange coordinate system, the distance from the projection of the center of the target ball on the X axis and the Z axis to the center of the target ball is constant, then the square of the fitting circle radius value R of the target ball rotating around the Y axis of the flange coordinate system is equal to: Y ​ ； (4) When the target ball rotates around the Z axis of the flange coordinate system, the projection of the center of the target ball on the X axis and the Y axis to the center of the ball is constant, and the square of the fitting circle radius R of the flange coordinate system around the Z axis is equal to: Z ​ ； The final equation set: ； Finally, the values of X, Y, and Z are solved, thereby determining the TCP of the target ball.

3. The method of claim 1, wherein: The X, Y, and Z positive directions of the target ball tool coordinate system are the same as the positive directions of the flange end coordinate system. Move two points along the X, Y, and Z axes by operating the industrial robot, and the specific steps are as follows: (1) make the industrial robot back to the initial pose P0, operate the industrial robot to move 100mm in the direction of the flange coordinate system X axis, record the reading of the first point under the robot flange coordinate system X p1 , move 100mm, record the reading of the second point X p2 , then the positive direction of the flange coordinate system X axis can be determined, the positive direction of the tool coordinate X axis of the target ball can be determined, and the positive and negative of the TCP point of the target ball can be determined simultaneously. (2) Repeat step (1) for the Y axis to determine the positive direction of the tool coordinate Y axis of the target ball; (3) Repeat step (1) for the Z axis to determine the positive direction of the tool coordinate Z axis of the target ball; (4) Input the TCP coordinates of the target ball into the robot control system, and the tool coordinate system of the target ball center can be obtained.

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