SenseKit to Robot Calibration

Guide to the calibration process of SenseKit with respect to the Robot.

The SenseKit to Robot Calibration is a crucial step in the optimization process that ensures seamless coordination between the SenseKit device and the robotic arm within the AMAS VR App. This calibration process is pivotal to achieving a level of precision that is fundamental for a truly immersive and accurate virtual reality robotics experience. Let's delve into the significance and intricacies of the SenseKit to Robot Calibration:

The Calibration Process: A Closer Look

Prerequisites

Make sure that the SenseKit and RoboKit is properly setup, and you have the Charuco Board handy as per the previous instructions.

Grab or place calibration board

If your camera is mounted in a stationary way:

  • go in to the Interaction panel, switch into the Robot Control Mode, turn on the Grip Mode and grab calibration board with robotic arm

If your camera is mounted on the robot gripper/end-effector and moving with the robot arm

  • place the calibration board close to the camera in such way that it is visible for the camera (for example on table with robotic arm)

Open the calibration panel

  1. Go to the Configuration Panel and click on SenseKit.

  2. Select SenseKit you want to calibrate in the list of Active SenseKits.

  3. In SenseKit configuration page click on Calibrate button located at the bottom of the right hand side panel.

  4. Select SenseKit to Robot calibration.

  5. Select RoboKit for the arm you want the camera to be calibrated to.

Select Mount Type

Select option depending on how your camera is mounted with respect to robot :

Base : hand-eye calibration, camera mounted in stationary way with respect to robot

End Effector : eye-in-hand calibration, camera mounted on the gripper/end-effector and moving with the robot

End Effector with Pose : like above but with camera data sent including synchronized pose data, currently only available in custom Extend Robotics setups.

Performing the Calibration

You should see SenseKit Calibration panel with:

  • information such as: Calibration Type, Sample Size, Position Error and Rotation Error.

  • buttons: Take Sample,Reset,Save and Cancel.

The Position Error and Rotation Error will be shown as zero until the 4th sample is taken as the software doesn't have enough data previously to calculate the error.

Make sure Robot Control Mode in enabled in Interaction panel for moving arm.

  1. Move the end effector position and rotation of the joint to change the angle at which the camera observes the calibration board and take your first sample by clicking on Take Sample.

  2. Repeat Step 1 three more times to reach a sub-optimal point where the SenseKit will align with the robot partially.

  3. Press Save if you're happy with the first result which will take you back to the Configuration Page of the SenseKit.

  4. Finally press Save Local or Save Local and Device to save the calibration done so far.

Usually the first four samples only achieve a partial calibration with high positional and rotational errors. We recommend repeating Step 2 from 5 to 20 times to fine-tune the calibration and decrease the error.

In case the calibration gets botched at any sample you can press Reset to reset to the last save and try from Step 1 again.

For best results make sure that calibration board is completely visible to the camera during the whole process. While Charuco calibration board supports partial views and occlusions this limits the number of markers possible to detect and potentially decreases accuracy of calibration.

Alternatively, fine-tuning can also be achieved using manual calibration. See Manual Sensekit Calibration for further instructions.

SenseKit to Robot Calibration Process

Improving calibration accuracy

Calibration accuracy may be improved by:

  • increasing the number of robot movements

  • maximizing the angular spread between robot movements

  • minimizing the distance between the camera and the calibration target

  • minimizing the distance moved by the robot arm between two positions

For detailed technical description of the problem see for example:

A Comparative Review of Hand-Eye Calibration Techniques for Vision Guided Robots

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