Mechanical arm calibration method based on single camera

Abstract

The invention relates to the technical field of mechanical arm calibration, in particular to a mechanical arm calibration method based on a single camera, which comprises the following steps: constructing a camera coordinate system and a mechanical arm coordinate system; the included angle between the straight line AB and the X axis under the mechanical coordinate system, the included angle between the straight line AB and the straight line BC, the included angle between the straight line BC and the straight line CD and the coordinates of the positioning point P under the mechanical arm coordinate system are obtained; driving the straight line BC to rotate twice at different angles so as to calculate the coordinate of the point B in the camera coordinate system, the rotation angle of the straight line BC in the camera coordinate system, the distance from the original point O of the camera coordinate system to the straight line BC and the distance from the perpendicular point Q to the point B; and calculating to obtain a conversion matrix between the coordinate of the positioning point P in the camera coordinate system and the coordinate of the positioning point P in the mechanical arm coordinate system. Calibration of the positioning point P can be achieved by rotating the shaft B twice, calibration operation steps can be simplified, and calibration accuracy and calibration efficiency are improved.

Description

Technical Field

[0001] This invention relates to the field of robotic arm calibration technology, and in particular to a robotic arm calibration method based on a single camera. Background Technology

[0002] In intelligent manufacturing, vision-guided robotic arm systems are widely used for tasks such as grasping and assembly. Their core lies in capturing images of target objects using a camera and converting them into coordinate commands that the robotic arm can execute. The key step in camera-guided robotic arm positioning is unifying the coordinate system of the robotic arm's end-effector with the camera coordinate system (i.e., hand-eye calibration).

[0003] Currently, calibration methods used in vision applications include: 1. N-point calibration method (e.g., nine-point calibration method, sixteen-point calibration method): During the calibration process, the end effector of the robotic arm needs to be operated to touch each point and simultaneously acquire image information (i.e., the tool and calibration point must be within the camera's field of view). However, this N-point calibration method is cumbersome to operate and is not suitable for scenarios where the end effector needs to be changed frequently. 2. Five-target calibration method: This method does not require human intervention and can adapt to dynamic and complex environments, but its accuracy is low and it requires complex algorithm support. Summary of the Invention

[0004] To address the shortcomings of existing production technologies, the applicant provides a single-camera-based robotic arm calibration method. By improving the calibration method, the calibration operation steps can be simplified, thereby improving calibration accuracy and efficiency.

[0005] The technical solution adopted in this invention is as follows: A single-camera-based robotic arm calibration method includes the following steps: S1. Construct the camera coordinate system Robotic arm coordinate system ; S2. Initial state: Obtain the angle between line AB and the X-axis in the machine coordinate system. The angle between lines AB and BC The angle between line BC and line CD The coordinates of the positioning point P in the robot arm coordinate system ; S3. Drive the straight line BC to rotate twice at different angles to calculate the coordinates of point B in the camera coordinate system. The rotation angle of line BC in the camera coordinate system The distance from the origin O of the camera coordinate system to the line BC The distance from point Q, the foot of the perpendicular from the origin O of the camera coordinate system to line BC, to point B. ; S4. Based on the data obtained in S2 and S3, calculate the coordinates of the positioning point P in the camera coordinate system. The coordinates of the positioning point P in the robot arm coordinate system The transformation matrix between them.

[0006] Therefore, by driving the B-axis to rotate twice to obtain the transformation matrix of the positioning point P in the camera coordinate system and the robot arm coordinate system, the positioning point can be calibrated. Compared with the existing calibration method, this method can calibrate the positioning point P by rotating the B-axis only twice, which can simplify the calibration operation steps and improve the calibration accuracy and efficiency. In addition, by driving the B-axis to rotate twice, it is ensured that the P point is within the camera's field of view.

[0007] Further, S3 includes the following steps: S3-1. Drive line BC to rotate twice at different angles to obtain the angle between line AB and line BC1. The coordinates of point C1 in the camera coordinate system The angle between line AB and line BC2 The coordinates of point C2 in the camera coordinate system

[0008] S3-2, Based on the included angle in S3-1 Coordinates of point C1 Angle Coordinates of point C2 The coordinates of point B in the camera coordinate system were calculated. ; S3-3, Based on the included angle in S3-1 Angle Coordinates of point B in S3-2 The rotation angle of line BC in the camera coordinate system is calculated.

[0009] S3-4. Obtain the distance from the origin O of the camera coordinate system to the line BC. The distance from point Q, the foot of the perpendicular from the origin O of the camera coordinate system to line BC, to point B. .

[0010] Furthermore, in S3-2, the angle between line C1B and line BC2 is... The calculation formula is: ; Slope of line C1C2 The calculation formula is: ; Inclination angle of straight line C1C2 The calculation formula is: ； isosceles triangle bottom corner The calculation formula is: ; Inclination angle of line BC1 The calculation formula is: ; Inclination angle of line BC2 The calculation formula is: ; The equation of line BC1 is expressed as: ; The equation of line BC2 is expressed as: ; By solving the equations BC1 and BC2 simultaneously, the coordinates of point B in the camera coordinate system can be obtained. .

[0011] Furthermore, in S3-3, the inclination angle of line BC is... The calculation formula is: ; The equation of line BC is then expressed as: ; Inclination angle of line BC That is, the rotation angle of line BC in the camera coordinate system. .

[0012] Furthermore, in S3-4, the distance from point Q, the foot of the perpendicular between the camera coordinate system origin O and line BC, to point B is... The calculation formula is: ; in: This represents the distance between point B and point C.

[0013] Furthermore, in S2, lines BC1 and BC2 are located on both sides of line BC.

[0014] Furthermore, in S4, the coordinates of the positioning point P in the camera coordinate system are... The coordinates of the positioning point P in the robot arm coordinate system The expression for the transformation matrix between them is: .

[0015] Furthermore, in S1, the camera coordinate system is defined by the image coordinate system.

[0016] Furthermore, in S1, the camera coordinate system Compared with the standard Cartesian two-dimensional rectangular coordinate system The transformation matrix between them is: .

[0017] Furthermore, in S1, the robotic arm coordinate system refers to: with point A as the origin, when points A, B, and C are collinear, the straight line AB is the X-axis, and the direction of the positive half-axis of the X-axis is the direction from point A to point B. The X-axis is rotated 90° counterclockwise around point A to obtain the Y-axis.

[0018] The beneficial effects of this invention are as follows: This invention achieves the calibration of the positioning point P by driving the B-axis to rotate twice to obtain the transformation matrix between the camera coordinate system and the robot arm coordinate system. Compared with existing calibration methods, this method can calibrate the positioning point P by rotating the B-axis only twice, which simplifies the calibration operation steps and improves calibration accuracy and efficiency. In addition, by driving the B-axis to rotate twice, it is ensured that point P is within the camera's field of view. Attached Figure Description

[0019] Figure 1 This is a flowchart of the single-camera-based robotic arm calibration method of the present invention; Figure 2 This is a diagram showing the positional relationship between points A, B, C, and D in the initial state of this invention. Figure 3 This is a diagram showing the positional relationship between the two sides of the B-axis in the initial state of the present invention. The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0020] like Figure 1 Figure 4 illustrates the preferred embodiment of the present invention. The single-camera-based robotic arm calibration method of this embodiment includes the following steps: S1. Construct the camera coordinate system Robotic arm coordinate system ; S2. Initial state: Obtain the angle between line AB and the X-axis in the machine coordinate system. The angle between lines AB and BC The angle between line BC and line CD The coordinates of the positioning point P in the robot arm coordinate system ; S3. Drive the straight line BC to rotate twice at different angles to calculate the coordinates of point B in the camera coordinate system. The rotation angle of line BC in the camera coordinate system The distance from the origin O of the camera coordinate system to the line BC The distance from point Q, the foot of the perpendicular from the origin O of the camera coordinate system to line BC, to point B. ; S4. Based on the data obtained in S2 and S3, calculate the coordinates of the positioning point P in the camera coordinate system. The coordinates of the positioning point P in the robot arm coordinate system The transformation matrix between the camera and robotic arm coordinate systems is obtained by driving the B-axis to rotate twice. This allows for the calibration of the positioning point P, which, compared to existing calibration methods, only requires two B-axis rotations to calibrate P, simplifying the calibration process and improving accuracy and efficiency. Furthermore, driving the B-axis to rotate twice ensures that P is within the camera's field of view.

[0021] It should be noted that since the height of the operating surface is fixed during the calibration process, only the horizontal and vertical coordinates need to be calibrated (i.e., only the following values ​​need to be obtained). and , and The correspondence between them is sufficient.

[0022] Specifically, a camera is installed on the side of the BC arm near the C-axis end. A single camera can reduce the hardware cost required for the entire calibration method, enabling high-precision positioning of the robotic arm guided by a single camera with a small field of view. At the same time, the camera is mounted on the side of the BC arm, which can adapt to the requirements of frequent changes of the end effector and maintain the accuracy of close-range positioning.

[0023] In this embodiment, in S1, the camera coordinate system is defined by the image coordinate system; In S1, the camera coordinate system Compared with the standard Cartesian two-dimensional rectangular coordinate system The transformation matrix between them is: ; The coordinate system of a robotic arm refers to the following: with point A as the origin, when points A, B, and C are collinear, the straight line AB is the X-axis, and the direction of the positive half of the X-axis is from point A to point B. The Y-axis is obtained by rotating the X-axis counterclockwise by 90° around point A.

[0024] In this embodiment, step S3 includes the following steps: S3-1. Drive line BC to rotate twice at different angles to obtain the angle between line AB and line BC1. The coordinates of point C1 in the camera coordinate system The angle between line AB and line BC2 The coordinates of point C2 in the camera coordinate system

[0025] S3-2, Based on the included angle in S3-1 Coordinates of point C1 Angle Coordinates of point C2 The coordinates of point B in the camera coordinate system were calculated. ; S3-3, Based on the included angle in S3-1 Angle Coordinates of point B in S3-2 The rotation angle of line BC in the camera coordinate system is calculated.

[0026] S3-4. Obtain the distance from the origin O of the camera coordinate system to the line BC. The distance from point Q, the foot of the perpendicular from the origin O of the camera coordinate system to line BC, to point B. ; In S3-2, the angle between line C1B and line BC2 is... The calculation formula is: ; Slope of line C1C2 The calculation formula is: ; Inclination angle of straight line C1C2 The calculation formula is: ； isosceles triangle bottom corner The calculation formula is: ; Inclination angle of line BC1 The calculation formula is: ; Inclination angle of line BC2 The calculation formula is: ; The equation of line BC1 is expressed as: ; The equation of line BC2 is expressed as: ; By solving the equations BC1 and BC2 simultaneously, the coordinates of point B in the camera coordinate system can be obtained. ; In S3-3, the inclination angle of line BC The calculation formula is: ; The equation of line BC is then expressed as: ; Inclination angle of line BC That is, the rotation angle of line BC in the camera coordinate system.

[0027] In S3-4, the distance from point Q, the foot of the perpendicular from the origin O of the camera coordinate system to line BC, to point B is... The calculation formula is: ; in: This represents the distance between point B and point C; Lines BC1 and BC2 are located on opposite sides of line BC.

[0028] In this embodiment, in S4, the coordinates of the positioning point P in the camera coordinate system are... The coordinates of the positioning point P in the robot arm coordinate system The expression for the transformation matrix between them is: .

[0029] In summary, by driving the B-axis to rotate twice to obtain the transformation matrix of the positioning point P in the camera coordinate system and the robot arm coordinate system, the positioning point can be calibrated. Compared with existing calibration methods, this method can calibrate the positioning point P by rotating the B-axis only twice, which simplifies the calibration operation steps and improves calibration accuracy and efficiency. In addition, by driving the B-axis to rotate twice, it is ensured that point P is within the camera's field of view.

[0030] The above description is an explanation of the present invention and not a limitation thereof. The scope of the present invention is defined by the claims. Within the scope of protection of the present invention, any form of modification may be made.

Claims

1. A method for calibrating a robotic arm based on a single camera, characterized in that, Includes the following steps: S1. Construct the camera coordinate system Robotic arm coordinate system ; S2. Initial state: Obtain the angle between line AB and the X-axis in the machine coordinate system. The angle between lines AB and BC The angle between line BC and line CD The coordinates of the positioning point P in the robot arm coordinate system ; S3. Drive the straight line BC to rotate twice at different angles to calculate the coordinates of point B in the camera coordinate system. The rotation angle of line BC in the camera coordinate system The distance from the origin O of the camera coordinate system to the line BC The distance from point Q, the foot of the perpendicular from the origin O of the camera coordinate system to line BC, to point B. ; S4. Based on the data obtained in S2 and S3, calculate the coordinates of the positioning point P in the camera coordinate system. The coordinates of the positioning point P in the robot arm coordinate system The transformation matrix between them.

2. The single-camera-based robotic arm calibration method as described in claim 1, characterized in that: S3 includes the following steps: S3-1. Drive line BC to rotate twice at different angles to obtain the angle between line AB and line BC1. The coordinates of point C1 in the camera coordinate system The angle between line AB and line BC2 The coordinates of point C2 in the camera coordinate system S3-2, Based on the included angle in S3-1 Coordinates of point C1 Angle Coordinates of point C2 The coordinates of point B in the camera coordinate system were calculated. ; S3-3, Based on the included angle in S3-1 Angle Coordinates of point B in S3-2 The rotation angle of line BC in the camera coordinate system is calculated. S3-4. Obtain the distance from the origin O of the camera coordinate system to the line BC. The distance from point Q, the foot of the perpendicular from the origin O of the camera coordinate system to line BC, to point B. .

3. The single-camera-based robotic arm calibration method as described in claim 1, characterized in that: In S3-2, the angle between line C1B and line BC2 is... The calculation formula is: ； Slope of line C1C2 The calculation formula is: ； Inclination angle of straight line C1C2 The calculation formula is: ； isosceles triangle bottom corner The calculation formula is: ； Inclination angle of line BC1 The calculation formula is: ； Inclination angle of line BC2 The calculation formula is: ； The equation of line BC1 is expressed as: ； The equation of line BC2 is expressed as: ； By solving the equations BC1 and BC2 simultaneously, the coordinates of point B in the camera coordinate system can be obtained. .

4. The single-camera-based robotic arm calibration method as described in claim 3, characterized in that: In S3-3, the inclination angle of line BC The calculation formula is: ； The equation of line BC is then expressed as: ； Inclination angle of line BC That is, the rotation angle of line BC in the camera coordinate system. .

5. The single-camera-based robotic arm calibration method as described in claim 4, characterized in that: In S3-4, the distance from point Q, the foot of the perpendicular from the origin O of the camera coordinate system to line BC, to point B is... The calculation formula is: ； in: This represents the distance between point B and point C.

6. The single-camera-based robotic arm calibration method as described in claim 1, characterized in that: In S2, lines BC1 and BC2 are located on opposite sides of line BC.

7. The single-camera-based robotic arm calibration method as described in claim 1, characterized in that: In S4, the coordinates of the positioning point P in the camera coordinate system are... The coordinates of the positioning point P in the robot arm coordinate system The expression for the transformation matrix between them is: 。 8. The single-camera-based robotic arm calibration method as described in claim 1, characterized in that: In S1, the camera coordinate system is defined by the image coordinate system.

9. The single-camera-based robotic arm calibration method as described in claim 8, characterized in that: In S1, the camera coordinate system Compared with the standard Cartesian two-dimensional rectangular coordinate system The transformation matrix between them is: 。 10. The single-camera-based robotic arm calibration method as described in claim 1, characterized in that: In S1, the robot arm coordinate system refers to: With point A as the origin, when points A, B, and C are collinear, the straight line AB is the X-axis, and the direction of the positive half of the X-axis is from point A to point B. The Y-axis is obtained by rotating the X-axis counterclockwise by 90° around point A.

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