3D Geometric Parameter Measurement Using Sinusoidal Alignment Patterns
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Solution Overview
Problem
Current methods for measuring 3D geometric parameters of an imaging system are limited by the need for precise alignment of a planar test chart, which is difficult to achieve and results in inaccurate measurements, especially when the object is oriented close to perpendicular to the optical axis, as seen in optical device manufacturing processes.
Innovation Solution
A method using specially constructed 2D target images with alignment patterns such as 2D scale and rotation invariant basis functions, 1D scale invariant basis functions, and sinusoidal patterns to determine geometric parameters from a single image, allowing accurate measurement of 3D parameters without requiring precise alignment of the measuring system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional feature detection methods are used to measure 3D geometric parameters, then the measurement process can be simplified, but the measurement precision deteriorates due to limited spatial resolution of feature detection
Solution Approach 1:
The patent transforms the detection problem from spatial domain to frequency domain by using sinusoidal patterns. Instead of detecting feature positions directly in space, the system modulates the test chart with sinusoidal patterns and analyzes the frequency content of captured images. This parameter transformation allows sub-pixel precision measurement because frequency can be determined with much higher precision than spatial position, thereby resolving the contradiction between simple measurement process and high measurement precision.
2Measurement precision
If many features are used to cover the surface area of the object to compensate for limited spatial resolution, then the measurement precision improves, but the device complexity and measurement time increase
Solution Approach 1:
The patent uses sinusoidal patterns that can be mathematically replicated and transformed across the test chart surface. Instead of requiring many discrete physical features, the system uses a small number of sinusoidal pattern copies at different orientations and frequencies. These patterns encode multiple measurement information channels, allowing high-precision geometric parameter extraction from minimal pattern instances, thus reducing the number of features needed while maintaining or improving measurement precision.
3Measurement precision
If the test chart is oriented perpendicular to the optical axis for ideal measurement, then the measurement precision improves, but the ease of operation deteriorates due to difficulty in achieving and verifying precise alignment
Solution Approach 1:
The patent measures the actual orientation and position parameters of the test chart by analyzing the frequency and phase information from sinusoidal patterns captured at different orientations. Instead of requiring the operator to manually align the chart perpendicular to the optical axis, the system automatically determines the chart's geometric parameters from the captured images and compensates for misalignment through computational analysis. This transforms the problem from mechanical alignment to computational measurement, greatly improving ease of operation while maintaining measurement precision.
Data Source
AI summary
Disclosed is a method of determining at least one three-dimensional (3D) geometric parameter of an imaging device. A two-dimensional (2D) target image is provided having a plurality of alignment patterns. The target image is imaged with an imaging device to form a captured image. At least one pattern of the captured image is compared with a corresponding pattern of the target image. From the comparison, the geometric parameter of the imaging device is then determined. The alignment patterns include at least one of (i) one or more patterns comprising a 2D scale and rotation invariant basis function, (ii) one or more patterns comprising a 1D scale invariant basis function, and (iii) one or more patterns having a plurality of grey levels and comprising a plurality of superimposed sinusoidal patterns, the plurality of sinusoidal patterns having a plurality of predetermined discrete orientations. Also disclosed is a two-dimensional test chart for use in testing an imaging device, the test chart comprising a plurality of alignment patterns, at least one of said alignment patterns including one of those patterns mentioned above.