Hi, I’m Xiaozhi. There is no urgent matter today, I ate a sausage powder in the morning and slowly walked to the company. It is the solar sun in Shenzhen that has dried off the skin, so I dare not ride to the company in the morning.

Xiaozhi updated a lot of hand-eye calibration articles on the public account, there are also a lot of students to use the library recommended by Xiaozhi to do calibration.

If not hand-eye calibration can be linked :mp.weixin.qq.com/s/886-kxRjT…

But the results were disappointing, and the resulting hand-eye matrix, the camera and the arm could be separated by thousands of meters. So today, small wisdom on the hand-eye calibration should have some matters needing attention.

The accuracy of hand-eye calibration depends on the accuracy of data.

According to the calibration principle, we can know that the input data is jointly determined by the pose of the manipulator and the pose of the calibration plate in the camera. Next, we will talk about several directions to improve the accuracy of the calibration results.

Graph LR A[manipulator pose] -->C[hand-eye calibration program] B[calibration plate pose] -->C C --> F[relationship between end and camera pose]

Several directions for improving accuracy

1. Accuracy of the pose data of the manipulator

Mechanical arm is usually data from the manufacturer to the SDK or can easily get in, and the accuracy is very accurate, but it is only at the end of the Angle, for our actual use, will install grip in the mechanical arm and suction cups, so at the end of the calibration accuracy mechanical arm, the manufacturer can use mechanical arm to the calibration procedure.

2. Accuracy of camera calibration

  • If the calibration target plate is a planar calibration plate similar to checkerboard format, a calibration plate with relatively high machining accuracy should be used
  • As many corners and images as possible. The calibration plate with more Angle points is recommended here. 10×10 is the minimum size that the original author believes should be used for the calibration plate, usually 20×20.
  • Use a wide range when taking pictures. Make sure that in some images the focus axis is aligned with the calibration plate at a large tilt
  • Care must be taken to reduce shaking and motion blur during photography, which can occur during calibration with ROS.

3. Accuracy of camera recognition results

Reference: blog.csdn.net/sandy_wym_/…

  • The Angle between two axes of rotation: the larger the better

  • The rotation matrix for each motion corresponds to the rotation Angle: the larger the better

  • Distance from camera center to calibration plate: the smaller the distance, the better

  • Distance of the end of the manipulator in each movement: the smaller the distance, the better

  • Influence on the accuracy of manipulator

Improve accuracy in several directions

  • No matter how many sets of motion data are collected for calibration, each set of motion maximizes the motion Angle.
  • Maximize the rotation axis Angle of the two groups of motion.
  • The movement distance of the end of the manipulator in each group should be as small as possible, which can be achieved through path planning.
  • Minimize the distance between the camera center and the calibration plate, and use a appropriately small calibration plate.
  • Collect as many sets of data as possible for solving.
  • High precision camera calibration methods are used.
  • The absolute positioning accuracy of the manipulator should be improved as much as possible. If this condition cannot be achieved, the relative motion accuracy should be improved at least.

Finally, welcome to pay attention to xiaozhi, share more dry goods ~