Interferometer Absolute Positioning Without a Stable Reference Axis
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Solution Overview
Problem
Existing interferometer systems are limited in determining the absolute position of movable objects due to the need for a stable reference axis and fast frequency modulating light sources, complicating the measurement process.
Innovation Solution
A method and system using two light sources with different frequencies, one fixed and one tunable, to calculate absolute position through a non-linear equation based on wavelength and count offsets, eliminating the need for a stable reference axis and complex frequency modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If relative position measurement between projection systems is used, then alignment can be achieved, but absolute position information is lost leading to drift errors
Solution Approach 1:
A laser interferometer measurement system is introduced as an intermediary between the projection systems and the alignment reference. This interferometer measures the actual positions of alignment marks with absolute precision, providing a mediator that translates relative alignment operations into absolute position information, thereby eliminating drift errors while maintaining alignment capability
Solution Approach 2:
The patent replaces traditional mechanical or optical alignment systems that only provide relative position information with a laser interferometer-based measurement system. This substitution introduces absolute position measurement capability, where the interferometer directly measures absolute positions of alignment marks rather than relying on relative measurements between projection systems
2Measurement precision
If alignment marks are measured with high precision, then positioning accuracy improves, but measurement time increases
Solution Approach 1:
Alignment marks are pre-designed with specific geometric features (such as known patterns, symmetries, or reference configurations) that enable rapid identification and measurement. The mark structures are prepared in advance to be optimally measurable by the interferometer, allowing high-precision absolute position determination without excessive measurement time
Solution Approach 2:
The alignment marks utilize optical contrast variations (analogous to color changes) where different regions of the marks have distinct optical properties that facilitate rapid detection and precise measurement by the interferometer system, enabling quick differentiation and accurate positioning
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 accurate determination of absolute position without requiring a stable reference axis or fast frequency modulation, simplifying the measurement process and expanding practical applications.
Implementation Method 1
laser interferometer measurement system
Data Source
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AI summary
A method to determine an absolute position of a first movable object using an interferometer system is described, said method comprising: providing first and second beams with a first light frequency from a first light source; providing further first and further second beams with a second (tunable) light frequency from a second light source; guiding the first and further first beams along a first axis to a reflective surface of the first object to obtain a first interferometer signal and guiding the second and further second beams along a second axis to a reflective surface of a second object to obtain a second interferometer signal, while changing the tunable frequency, detecting the first and further first interferometer signals, detecting the second and further second interferometer signals, determining a first count offset and/or a further first count offset using a non-linear equation, and determining the absolute position of the first object.