Interferometer Calibration Using Defined Coordinate System
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Solution Overview
Problem
Existing interferometric calibration methods face limitations in achieving accurate optical path length calculations due to positioning errors and ambiguities, particularly when measuring aspherical surfaces, leading to incorrect calibrations and reduced measurement accuracy.
Innovation Solution
The method employs multiple calibration objects with differently curved surfaces and a defined coordinate system using predetermined coordinate values to ensure precise calibration, eliminating scaling errors and improving convergence, allowing for accurate measurement of optical path lengths across the interferometer, including non-zero test configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional interferometric calibration methods are used, then calibration can be performed with standard procedures, but positioning errors and ambiguities lead to incorrect optical path length calculations and reduced measurement accuracy
Solution Approach 1:
The patent introduces secondary conditions as additional parameters to fix the coordinate system origin and orientation. These parameters constrain the calibration process by defining specific relationships between measurement points, thereby eliminating ambiguities in optical path length calculations and improving both measurement precision and calibration reliability
Solution Approach 2:
The patent uses a coordinate system with defined origin and orientation as an intermediary framework to relate measurement points to the interferometer's optical paths. This intermediary coordinate system mediates between the physical measurement positions and the calculated optical path lengths, resolving ambiguities and improving calculation accuracy
2Measurement precision
If multiple calibration objects with differently curved surfaces are used, then calibration accuracy and convergence are improved, but the complexity of the calibration process increases
Solution Approach 1:
The patent employs multiple calibration objects with differently curved surfaces (spherical, aspherical, free-form) that can be measured using the same interferometric setup and evaluation methodology. This multi-functional approach allows a single calibration procedure to validate the system across various surface types, improving calibration accuracy without requiring separate specialized procedures for each object type
Solution Approach 2:
By varying the surface curvature parameters of the calibration objects (from spherical to aspherical to free-form), the patent creates a comprehensive calibration dataset that constrains more parameters of the computational model. This parameter variation improves calibration accuracy by eliminating scaling errors and improving convergence, while the systematic approach manages the increased complexity
3Measurement precision
If a coordinate system with predetermined coordinate values is defined, then scaling errors are eliminated and convergence is improved, but the flexibility in coordinate system selection is reduced
Solution Approach 1:
The patent fixes specific coordinate parameters (origin position and orientation angles) as predetermined values to eliminate scaling errors and improve convergence. By constraining these parameters, the system achieves more accurate and reliable calibration results, while other coordinate parameters remain flexible for adapting to different measurement scenarios
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
This approach enhances calibration accuracy and reduces adjustment requirements, enabling the measurement of aspheres and free-form surfaces with higher deviations from nominal shapes, and improves convergence by allowing calibration of systems with larger deviations, up to fifty times the wavelength, compared to traditional methods.
Implementation Method 1
The test wave and the reference wave are preferably generated from coherent light from one and the same light source... The test wave is reflected or refracted at the interface and then superimposed on a detector, for example a light-sensitive chip of a camera, with a reference wave... The resulting interference pattern is therefore undesirably ambiguous.
Implementation Method 2
An optically smooth surface is a specularly reflecting boundary surface... The test wave is reflected or refracted at the interface...
Implementation Method 3
An optically smooth surface is a specularly reflecting boundary surface or a smooth, light-refracting boundary surface of a transparent object... The test wave is reflected or refracted at the interface...
Data Source
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AI summary
The invention relates to a method for calibrating a measuring device, comprising the following steps: moving, with finite accuracy and thus with positioning error, to various points that lie in a testing volume of the measuring device and that can be characterized by spatial and/or angular coordinates, generating measurement signals at the respective points, and determining parameters of a computing model of the measuring device from the measurement signals and the spatial and/or angular coordinates. The method is characterized in that a coordinate system to which the coordinates of the points of the testing volume relate is defined from points moved to with error, by associating predetermined coordinate values with exactly six coordinates of three points.