Robot Calibration Marker Positioning for Kinematic Parameter Identification
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Solution Overview
Problem
Current robot calibration methods are complex and costly, often requiring external high-precision measurement systems or simultaneous optimization of robot and camera parameters, which limits accuracy and increases complexity, especially for field calibration of vision-guided robots.
Innovation Solution
A method that uses a calibration marker positioned along the optical line of a camera to separate the identification of robot kinematic parameters from camera parameters, eliminating camera errors and simplifying the optimization process, allowing for high-accuracy calibration without additional hardware beyond the existing robot camera.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If external high-precision measurement systems (e.g., laser trackers) are used for robot calibration, then manufacturing precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the calibration marker from the complex external measurement system and positions it directly on the robot's movable part. This simple marker can be imaged by the robot's existing camera, eliminating the need for expensive external measurement systems like laser trackers while maintaining calibration accuracy.
Solution Approach 2:
The robot uses its own camera to image the calibration marker, performing self-calibration without external measurement equipment. The robot's existing vision system serves the dual purpose of both operation and calibration, reducing device complexity and cost.
2Measurement precision
If simultaneous optimization of robot and camera parameters is performed, then measurement precision is improved, but device complexity and computational difficulty increase
Solution Approach 1:
The patent segments the calibration process into two independent parts: first calibrating the robot by optimizing only robot kinematic parameters, then separately calibrating the camera. This segmentation transforms a complex simultaneous optimization problem with multiple unknown parameters into simpler sequential optimization problems, reducing computational difficulty while maintaining accuracy.
3Measurement precision
If additional sensors or devices are installed for calibration, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the robot's existing camera serve multiple functions: both for the robot's vision-guided operation and for calibration measurements. The calibration marker is positioned on the robot itself, allowing the same camera to perform both tasks without requiring additional sensors or devices.
4Device complexity
If self-calibration methods using constraints are used, then device complexity is reduced, but measurement precision deteriorates due to friction uncertainties
Solution Approach 1:
The patent introduces a calibration marker as an intermediary object that mediates between the robot and the camera. This marker provides precise visual features for measurement without requiring direct contact or constraint-based methods, thereby maintaining simplicity while achieving high accuracy by eliminating friction uncertainties associated with self-calibration methods.
Data Source
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AI summary
A method for calibrating a robot, wherein the robot comprises a movable part with a calibration marker. The method comprising: positioning the calibration marker in a plurality of positions along an optical line of a camera unit; imaging the calibration marker at the plurality of positions along the optical line to establish line positions P 1 ... P N of the calibration marker along the optical line within a tolerance k, while monitoring joint values j 1 ... j M of the robot; establishing an error function based on resulting calculated robot positions P' 1 ... P' N for the calibration marker for joint values j 1 ... j M at each line position P 1 ... P N for the calibration marker; identifying a set of robot kinematic parameters by solving an optimization problem based on the error function; and updating a kinematic model of the robot by means of the identified set of robot kinematic parameters. It is also referred to a robot system, a robot controller, a robot unit, use of a robot unit, a computer program P and a computer readable storage medium.