Robot Calibration Using End Effector Marker
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Solution Overview
Problem
Current methods for calibrating a camera's coordinate system to a robot's coordinate system are time-consuming, inaccurate, and require manual intervention, especially when using 2D checkboards, which are not suitable for 3D applications and cannot be permanently attached to the robot due to size constraints.
Innovation Solution
A method that uses a 2D calibration marker attached to the robot's end effector, allowing for automatic calibration by moving the end effector through a series of target points and orientations to calculate intrinsic and extrinsic parameters, enabling accurate calibration without manual intervention or the need for a large checkerboard.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a 2D checkerboard is used for calibration, then the calibration procedure can be performed, but it requires considerable size to give good calibration accuracy and cannot be permanently attached to the robot
Solution Approach 1:
The patent transitions from 2D checkerboard calibration to 3D calibration by attaching a compact 3D calibration object (such as a calibration sphere or multi-point 3D marker) to the robot end effector. This 3D structure provides sufficient calibration accuracy while maintaining a small size that can be permanently mounted on the robot, resolving the contradiction between calibration accuracy and object size.
2Extent of automation
If manual calibration is performed with a 2D checkerboard, then calibration can be done, but it takes long time and gives poor results with no feedback on accuracy
Solution Approach 1:
The patent implements automated calibration where the robot system itself performs the calibration process without manual intervention. The calibration object with known 3D coordinates is automatically detected by the camera, and the system automatically computes the transformation between camera and robot coordinate systems, eliminating the need for manual TCP definition and jog operations while providing feedback on calibration accuracy.
3Adaptability or versatility
If a large checkerboard is constantly attached to the tool flange for periodic calibration, then calibration can be re-done, but it becomes unpractical
Solution Approach 1:
The patent replaces the large 2D checkerboard with a compact 3D calibration object that can be permanently attached to the robot end effector. This 3D structure maintains recalibration capability while being small enough for practical permanent mounting, allowing periodic calibration without the impracticality of constantly attaching large checkers.
4Measurement precision
If traditional manual calibration is used, then calibration can be performed, but it is difficult to point out accurate TCP and work object on the checkerboard
Solution Approach 1:
The system uses the calibration object with precisely defined 3D coordinates that are automatically detected by the camera system. The robot automatically moves to and detects the calibration object positions, eliminating the need for manual pointing and definition of TCP and work object points, thereby improving both accuracy and ease of operation.
Data Source
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AI summary
The disclosure relates to a method and a system for calibrating a first coordinate system Rf of a robot unit with a second coordinate system Cf of an object identification unit, wherein the robot unit comprises a robot arm with an end effector and the object identification unit comprises a camera unit. The calibration is performed using a calibration marker on the end effector. The method determines the intrinsic and the extrinsic parameters of the camera unit in two steps, a first step where the intrinsic parameters and a rotational part of the extrinsic parameters are determined, and a second step where a translational part of the extrinsic parameters are determined.