Robot Calibration With Pivot-Pose Ballbar Measurement
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Solution Overview
Problem
Calibrating articulated robots is challenging due to cumulative positional errors from multiple joints, and existing methods like laser trackers are expensive and slow, while other techniques require complex setups and multiple measurements.
Innovation Solution
A method involving a pivot pose with a known separation between a target point and a pivot point, using a length-measuring device like a ballbar to determine error values, and iteratively updating model parameters to minimize overall error, along with an adaptor for precise measurement on the robot's tool centre point, and an extension part for the ballbar to enhance travel range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser trackers are used for calibration, then measurement precision is improved, but productivity deteriorates due to expensive and slow implementation
Solution Approach 1:
The patent replaces expensive laser tracker systems with a mechanical ballbar measurement system. The ballbar uses simple mechanical balls and distance measurement capabilities to achieve calibration, eliminating the need for complex optical laser tracking infrastructure while maintaining adequate measurement precision for robot calibration applications.
Solution Approach 2:
The patent employs inexpensive ballbar components (mechanical balls, simple measurement devices) instead of costly laser trackers. These simpler mechanical elements are sufficient for the calibration task and can be easily replaced or reset, providing a cost-effective and faster alternative to expensive laser-based systems.
2Measurement precision
If multiple measurements and complex setups are used, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts and focuses on a single critical measurement element - the ballbar distance measurement between two points. By isolating this essential measurement function and removing unnecessary complex setup procedures, the system achieves adequate calibration precision with significantly reduced device complexity and easier operation.
Solution Approach 2:
The ballbar system serves multiple calibration functions with a single simple device. It can measure distances in various robot configurations and positions, replacing the need for multiple specialized measurement tools and complex setup procedures, thereby reducing overall device complexity while maintaining measurement precision.
Data Source
AI summary
A method of calibrating a coordinate positioning machine is described. The machine is controlled into a pivot pose in which a target point associated with a moveable part of the machine and a pivot point associated with a fixed part of the machine are separated from one another by a known separation. An error value for that pose is determined based on the known separation and a separation expected for that pose from the existing model parameters of the machine. The machine is controlled into a plurality of different target poses, and for each target pose a separation between the target point and the pivot point is measured and an error value for that pose is determined based on the measured separation and a separation expected for that pose from the existing model parameters.