Qualitative calibration validation

Attention

This validation method relies on a human operator visually confirming the correctness of a calibration, hence is a coarse check.

Pickit also allows to perform a quantitative calibration, which is more accurate, and recommended for applications that need to keep an eye on sources of picking errors.

To inspect the details of the existing calibration, click the Calibration button on the top bar of the Pickit web interface. You will be presented with a summary of the last calibration associated to the active camera. If no calibration has been ever performed, it will also be indicated.

Calibration summary listing Last calibration date and time, Camera mount (Robot Mounted) and a Show details link for Technical frame information

Once Pickit thinks it knows where the robot is, it places two new frames in the 3D environment: the robot base and the robot flange frames. Their pose relatively to the camera frame should correspond to the actual transformations between robot base, flange and camera in the real world. It is recommended to have a look from different viewpoints to verify that the position and orientation of the robot base and flange frames look correct.

Fixed camera above a UR robot holding the calibration plate, next to the 3D view showing the point cloud of the robot and plate with the camera frame 3D view of the point cloud with the camera frame and the robot_base frame circled, positioned at the base of the robot

Checking robot-camera calibration with a UR robot

If you have a Universal Robots robot, you can additionally visualize a virtual 3D robot, which should make it easier to verify the correctness of calibration. To do so, follow these steps:

  1. Make sure there is communication between Pickit and the robot:

    Top bar icons with a check mark on the robot icon, indicating that Pickit communicates with the robot

  2. Navigate to the 3D view and click on the settings button on the lower right of the viewer.

    Viewer settings button (gear icon)

  3. Toggle the Visualize Robot check box.

    Viewer settings with the Visualize Camera and Visualize Robot check boxes enabled, Background color and Point size options

This allows you to intuitively check whether the virtual 3D robot aligns well with the displayed coordinate frames and captured point cloud. For example, the following images show a fixed-camera scenario where the robot is inside the camera view volume. It can be seen how, before calibration, the robot as seen by the camera does not align with the virtual 3D robot. After calibration they nicely align. Similarly, the attached calibration plate (only visible to the camera, not part of the virtual 3D robot) is correctly aligned with respect to the robot flange after calibration.

3D view before calibration: the point cloud of the robot seen by the camera does not align with the virtual 3D UR robot 3D view after calibration: the point cloud of the robot and calibration plate aligns well with the virtual 3D UR robot, with Visualize Robot enabled

Invalid robot-camera calibration?

If the outcome of calibration validation is that the current calibration is invalid, the most likely cause is that the camera moved with respect to the robot base (fixed camera) or robot flange (camera on robot). When this is the case, robot-camera calibration needs to be performed again.

If the camera has not moved with respect to the robot, it could be that something went unexpectedly wrong during calibration. The following pointers can help you identify the cause:

  • The calibration plate moved during the calibration process.

  • The camera mount (fixed or robot-mounted) was incorrectly selected in the calibration wizard.

  • For multi poses calibration, the calibration poses don’t comply with the recommendations.

  • For single pose calibration, the helper transformation is incorrect.

  • If you are integrating a new robot brand with Pickit, there might be an incompatability in the way poses are communicated between Pickit and the robot.

Note

If you are having trouble with robot-camera calibration, contact our support team by sending an email to support@pickit3d.com.