Auto-focus Method for Coordinate-Measuring Apparatus
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Solution Overview
Problem
Coordinate-measuring machines face challenges in quickly and reproducibly determining the focused image distance of optical sensors, especially when operating outside the depth of field region, leading to prolonged auto-focusing times and reduced reproducibility.
Innovation Solution
A method involving the assessment of image intensity at two focal distances to determine the most probable location of best focus, followed by approximation using three focal distances, allowing for quick determination of best focus even outside the depth of field region, combined with a contrast evaluation step for precise focus location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the optical sensor is moved through a large search region to ensure the best focus is found, then the reliability of focus determination is improved, but the auto-focusing time increases significantly
Solution Approach 1:
The focus determination process is divided into two distinct phases: a coarse determination phase that quickly identifies the approximate best focus position using intensity criteria, and a fine determination phase that precisely locates the best focus using contrast criteria. This segmentation allows the system to efficiently navigate large search regions while maintaining high reproducibility.
Solution Approach 2:
The coarse determination step is performed as a preliminary action before the fine determination step. By first using the intensity criterion to narrow down the search region and identify the approximate best focus position, the system prepares the groundwork for the subsequent precise contrast-based evaluation, reducing the overall time required while ensuring reliability.
2Measurement precision
If the optical sensor moves slowly through the search region to capture multiple images, then the measurement precision of focus location is improved, but the productivity of the measurement process decreases
Solution Approach 1:
The measurement process is segmented into two stages with different speed and precision characteristics. The coarse determination stage operates quickly with lower precision requirements, while the fine determination stage operates more slowly to achieve high precision. This segmentation allows the system to maintain high productivity overall while ensuring accurate focus location when needed.
Solution Approach 2:
The system performs a minimal necessary number of image evaluations in the coarse determination phase using intensity criteria, then focuses computational resources on a reduced set of candidate positions in the fine determination phase. This partial action approach avoids unnecessary slow movements and evaluations, maintaining productivity while achieving the required precision.
3Adaptability or versatility
If the search region for auto-focusing is increased to accommodate varying magnifications and large catchment regions, then the adaptability of the system is improved, but the complexity of the focusing process increases
Solution Approach 1:
The complex focusing problem is segmented into two manageable sub-problems: coarse determination using intensity criteria and fine determination using contrast criteria. This segmentation simplifies the overall process by breaking down the complexity of handling large search regions and varying magnifications into distinct, easier-to-manage stages.
Solution Approach 2:
The coarse determination step serves as a preliminary action that simplifies the subsequent fine determination step. By first identifying the approximate best focus position and narrowing down the search region, the system reduces the complexity of the subsequent precise evaluation, making the overall process more manageable despite the large initial search region requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid and reproducible determination of the best focus location, reducing the number of necessary image recordings and improving measurement accuracy, even with large catchment regions and varying magnifications.
Implementation Method 1
assessment of image intensity at two focal distances to determine the most probable location of best focus
Data Source
AI summary
A method is disclosed for ascertaining a focus image distance of an optical sensor, which is provided with a lens, of a coordinate-measuring apparatus onto a workpiece to be measured, wherein the optical sensor and/or the workpiece are movable in a Z direction such that a distance in the Z direction between the workpiece and the optical sensor is variable. Further, a corresponding coordinate-measuring apparatus and a computer program product are disclosed.