Camera Calibration

Description

The end effector and the camera must be calibrated for precise robot operation, allowing the system to accurately translate visual data into coordinated movements.

 

Calibration is performed by recording camera images and matching them with the robot poses. A special calibration board, with fixed positions, is used to recognize camera orientation.

 

The result of the calibration is the camera calibration file stored on the compute module ( ros/config/env.json).

 
Repeating the calibration

It is necessary to perform the calibration again after making any changes that affect the position of the camera on the robot. These might be any adjustments to the camera mount, replacement of the gripper or tightening of the bolts that hold the camera on the tool flange.

 
Adjusting robot payload

Ensure that you are using the correct Payload and Center of Gravity (CoG). Incorrect payload may result in Robot arm movement when pressing the Freedrive button.

You can use the Payload Estimation Wizard in PolyScope to assess the Payload and CoG.

 
Preparing for calibration

A calibration board is required to calibrate the camera. You can find and print a calibration board in the calib.io pattern generator. You can also adjust the grid and cell size in the Calibration Studio URCap. Make sure the printed board has the correct dimensions, as printer driver can introduce some scaling.

To set up your calibration board:

  • Position the calibration board inside the robot reach area, where you can move the robot arm maintaining the distance of 20cm to 80 cm between the camera and the board.

  • Do not make any adjustments to the position of the calibration board during the calibration.

  • The Calibration board must be evenly lit. Avoid shadows, for example from robot arm or operators body.

You can improve calibration accuracy by tapping Replay. The robot automatically moves through all manually recorded poses and re-takes images of the calibration board.

Stand outside the robot reach, robot will move automatically.

 
To calibrate the camera

  1. Launch the Calibration Studio URCap on the robot.

  2. Tap the gear button and configure the Compute module IP address.

  3. Tap Apply.

  4. Tap Manual to start recording the calibration images.

  5. Position the robot such way that calibration board is fully in camera view and there are some margins on all sides of the board. Tap Mark waypoint.

    Calibration board does not have to be inside the region of interest (light blue rectangle).

  6. Blue square flashes in top left corner of the live view.

  7. If a red square flashes, the calibration board was not recognised.

  8. You can also follow the calibration process in the terminal connected to the Compute module.

  9. Record at least 12 images varying the robot poses, including the rotation of the tool flange. Tap Done after taking all images.

  10. In the pop-up check the calibration results and press Confirm.
Finishing calibration

The calibration data is stored in: ros/config/env.json

Translation x,y,z are recorded in meters and should match camera offset from the robot's tool flange.