Calibration Principles
This topic describes the working principles of calibrations in different scenarios.
Hand-Eye Calibration in the ETH Setup (Multiple Random Calibration Board Poses)
When the hand-eye calibration is performed using the multiple random calibration board poses method in the ETH setup, it is assumed that the poses and their relative relationships are shown in the table below.
| Pose | Relationship | Note |
|---|---|---|
A |
Pose of the robot flange relative to the robot base |
Available from the robot side |
B |
Pose of the calibration board relative to the camera |
Can be obtained by capturing an image with the camera and calculating |
C |
Pose of the calibration board relative to the robot flange |
Constant in the extrinsic parameter calibration, used for establishing the equations |
X |
Pose of the camera relative to the robot base |
The result of the extrinsic parameter calibration, to be calculated |
As shown below, A, B, C, and X form a closed loop. By moving the robot and changing poses of the calibration board relative to the camera, a set of equations can be formed. Then, these values can be used to perform numerical fitting and obtain an optimal solution of X.
Hand-Eye Calibration in the EIH Setup (Multiple Random Calibration Board Poses)
When the hand-eye calibration is performed using the multiple random calibration board poses method in the EIH setup, it is assumed that the poses and their relative relationships are shown in the table below.
| Pose | Relationship | Note |
|---|---|---|
A |
Pose of the robot flange relative to the robot base |
Available from the robot side |
B |
Pose of the calibration board relative to the camera |
Can be obtained by capturing an image with the camera and calculating |
C |
Pose of the calibration board to the robot base |
Constant in the extrinsic parameter calibration, used for forming the equations |
X |
Pose of the camera relative to the robot flange |
The result of the extrinsic parameter calibration, to be calculated |
As shown below, A, B, C, and X form a closed loop. By moving the robot and changing poses of the calibration board relative to the camera, a set of equations can be formed. Then, these values can be used to perform numerical fitting and obtain an optimal solution of X.
Hand-Eye Calibration in the ETH Setup (TCP Touch)
When the hand-eye calibration is performed using the TCP touch method in the ETH setup, it is assumed that the poses and their relative relationships are shown in the table below.
| Pose | Relationship | Note |
|---|---|---|
A |
Pose of the robot flange relative to the robot base |
Available from the robot side |
B |
Pose of the calibration board relative to the camera |
Can be obtained by capturing an image with the camera and calculating |
C |
Pose of the TCP relative to the robot flange (TCP coincides with the calibration board when the tip of the TCP touches the calibration board) |
Constant in the extrinsic parameter calibration, used for forming the equations |
X |
Pose of the camera relative to the robot base |
The result of the extrinsic parameter calibration, to be calculated |
As shown below, A, B, C, and X form a closed loop. By moving the robot and changing poses of the TCP relative to the camera, a set of equations can be formed. Then, these values can be used to perform numerical fitting and obtain an optimal solution of X.
Hand-Eye Calibration in the EIH Setup (TCP Touch)
When the hand-eye calibration is performed using the TCP touch method in the EIH setup, it is assumed that the poses and their relative relationships are shown in the table below.
| Pose | Relationship | Note |
|---|---|---|
A |
Pose of the robot flange relative to the robot base |
Available from the robot side |
B |
Pose of the calibration board relative to the camera |
Can be obtained by capturing an image with the camera and calculating |
C |
Pose of the calibration board to the robot base |
Constant in the extrinsic parameter calibration, used for forming the equations |
X |
Pose of the camera relative to the robot flange |
The result of the extrinsic parameter calibration, to be calculated |
As shown below, A, B, C, and X form a closed loop. By moving the robot and changing poses of the calibration board relative to the camera, a set of equations can be formed. Then, these values can be used to perform numerical fitting and obtain an optimal solution of X.
Hand-Eye Calibration in the ETE Setup
Using double cameras can expand the camera field of view and improve the point cloud quality of the two cameras’ overlapping part, as shown in the following figure.
In the eye-to-eye (ETE) setup, two cameras, one as main camera and the other as sub-camera, are mounted on a stand independent of the robot. ETE calibration will not only calibrate the extrinsic parameters for the two cameras, but also calibrate the pose relationship between the two cameras. For the ETE setup, Mech-Vision provides a standard ETE calibration procedure.
Please pay attention to the following issues when performing ETE calibration:
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New calibration
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Mounting the two cameras in the EIH setup is not supported. If the cameras have to be mounted in the EIH setup, you can view the fusion effect for dual camera calibration through the Mech-Vision project.
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Loading existing calibration parameters
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The calibration parameter group of dual camera can be directly calculated based on the calibrated parameter groups of two cameras in the ETH or EIH setup.
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Checking the point cloud view by loading existing calibration parameters is not supported.
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