Global Calibration for Stereo Vision Touch Probe
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Solution Overview
Problem
Existing touch probe coordinate measuring systems face limitations in measurement accuracy due to camera frame distortion errors and probe form errors, which are not efficiently addressed by current calibration methods that often require separate procedures and additional marker arrangements, making them costly and complex, especially for desktop systems intended for unskilled users.
Innovation Solution
A global calibration method for multi-view vision-based touch probe systems that uses a portable calibration jig and iterative processes to determine camera frame distortion errors independently of probe form errors, relying solely on markers on the touch probe, and employs principal component analysis to establish a local coordinate system for accurate probe tip positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate calibration procedures are used for camera frame distortion errors and probe form errors, then measurement accuracy can be improved, but device complexity and cost increase
Solution Approach 1:
The patent combines separate calibration procedures for camera frame distortion errors and probe form errors into a single integrated global calibration process. The calibration jig includes both camera calibration features and probe calibration features that can be measured simultaneously, allowing both error types to be corrected in one unified procedure rather than requiring multiple separate calibrations.
Solution Approach 2:
The calibration jig is designed as a universal reference object that serves multiple functions: it provides reference features for camera frame distortion calibration, probe form calibration, and potentially other calibration needs. This multi-functional design eliminates the need for multiple specialized calibration objects and reduces overall system complexity.
2Measurement precision
If additional marker arrangements are used for calibration, then measurement accuracy improves, but cost and device complexity increase
Solution Approach 1:
The calibration jig integrates multiple calibration functions into a single reference object with strategically placed features. The jig includes camera calibration features (such as a calibration camera or camera calibration marks) and probe calibration features (such as a calibration probe with known geometry), allowing one object to perform multiple calibration tasks that would traditionally require separate objects or marker arrangements.
Solution Approach 2:
The calibration jig is segmented into distinct functional regions with specific features for different calibration purposes. The jig includes a body with embedded calibration features that can be independently identified and processed by the vision system, allowing structured calibration data extraction without requiring complex or numerous separate markers.
3Measurement precision
If complex calibration procedures are used, then measurement accuracy improves, but ease of operation decreases
Solution Approach 1:
The calibration process is designed to be self-service oriented, where the calibration jig automatically provides all necessary reference information when positioned in the measurement volume. The system automatically identifies calibration features, extracts calibration data, and performs corrections without requiring skilled operators to manually configure complex calibration procedures or interpret calibration results.
Solution Approach 2:
All calibration reference information is pre-encoded in the calibration jig during manufacturing. The jig includes pre-positioned calibration features with known geometric relationships that are ready for immediate use. This preliminary preparation eliminates the need for operators to perform complex calibration setup procedures during actual measurement operations.
Data Source
AI summary
A method for global calibration of a multi-view vision-based touch probe measurement system is provided which encompasses calibrating camera frame distortion errors as well as probe form errors. The only required features in the calibration images are the markers on the touch probe. The camera frame distortion calibration comprises a process that depends on a portable calibration jig and the touch probe, but that process is unaffected by probe form distortion errors in the touch probe and/or tip. The probe tip position calibration depends on applying the results of the camera, frame distortion calibration. When the same probe tip is used throughout the global calibration, the probe tip position calibration uses images from the set of images used by the camera frame distortion calibration. The global calibration method is particularly advantageous for low cost portable versions of multi-view vision-based touch probe measurement systems.