Camera Calibration Using Ring Jig and Parallel Axis Alignment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current camera calibration methods for measuring hole shapes in machine tools are complex due to the need to determine numerous interior and exterior parameters, including distortion correction coefficients and rotational angles, which complicates the calibration process.
Innovation Solution
A ring-shaped calibration jig is used to simplify the calibration process by ignoring distortion correction coefficients and aligning the camera's optical axis parallel to the machine tool's coordinate system, allowing for the calculation of the center position of the calibration jig and translation distance, thereby reducing the number of parameters to be determined.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional camera calibration methods are used to determine all interior and exterior parameters including distortion correction coefficients, then measurement accuracy is improved, but the calibration process complexity increases significantly
Solution Approach 1:
The patent extracts and eliminates the distortion correction parameters from the calibration process. By recognizing that distortion correction is unnecessary for the specific measurement task (measuring hole centers), the calibration process only determines the essential exterior parameters (rotation and translation), significantly reducing complexity while maintaining measurement accuracy for the intended application
Solution Approach 2:
The patent applies partial calibration by determining only the necessary parameters for the specific measurement task rather than performing complete camera calibration. Since the application only requires accurate hole center measurement and not general image measurement accuracy, only the essential exterior parameters are calibrated, avoiding the excessive action of determining all possible camera parameters
2Measurement precision
If a complex calibration jig with multiple features is used to enable comprehensive parameter determination, then calibration accuracy is improved, but the ease of manufacture and attachment deteriorates
Solution Approach 1:
The patent simplifies the calibration jig to contain only the essential feature needed for the calibration purpose - a circular pattern for determining exterior parameters. By removing unnecessary complex features from the calibration jig, it becomes much easier to manufacture and attach while still providing sufficient information for accurate calibration of the required parameters
Solution Approach 2:
The calibration jig is designed with local quality - it has the specific circular pattern feature exactly where and in the form needed for exterior parameter determination. The jig's structure is optimized locally for its specific function rather than incorporating universal features, making it simple to manufacture while maintaining calibration accuracy
Data Source
AI summary
In a calibration method a ring-shaped jig is disposed on a machine tool workpiece. The optical axis of a camera is aligned parallel to an axis of the machine tool. The jig is photographed with the horizontal or the vertical direction of the camera aligned with an axial direction other than the signal direction of the machine tool. The circumferential shape of the jig in the photograph is extracted as a contour. The center position of the jig in the image is calculated from the contour while all distortion correction coefficients in tangential and radial directions are ignored and set to zero. The displacements of the main point of the camera are set to zero. The translation distance, which is an external parameter of calibration, is calculated based on the center position of the jig in the image and the known three-dimensional center position of the jig.