Interferometer Position Measurement System
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Solution Overview
Problem
Position measurement systems based on optical path length differences are sensitive to humidity, temperature, wavelength variations, and refractive index changes in the surrounding air, especially when the optical path length is large.
Innovation Solution
A position measurement system comprising two interferometers, where each interferometer forms a reference beam by reflection from a reflective element and a measurement beam by diffraction from a grating on the object, with the reflective element of one interferometer serving as the reference for the other, allowing the input radiation of both interferometers to be incident at substantially the same location on the grating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If optical path length is increased to improve measurement range, then measurement range is improved, but sensitivity to environmental variations (humidity, temperature, wavelength, refractive index) increases
Solution Approach 1:
The patent transitions from a conventional linear optical path configuration to a folded optical path configuration using mirrors. This dimensional change allows the optical beam to traverse a longer effective measurement path while maintaining a compact physical footprint, thereby extending measurement range without proportionally increasing environmental sensitivity
Solution Approach 2:
The patent implements a nested optical path structure where the optical beam folds back through the same physical space multiple times using mirrors. This nesting approach allows the light to cover an extended optical path length within a confined physical volume, achieving long measurement range without the linear expansion that would increase environmental exposure
2Measurement precision
If optical path length is increased to improve measurement resolution, then measurement resolution is improved, but sensitivity to humidity, temperature, wavelength variations and refractive index changes increases
Solution Approach 1:
By folding the optical path in multiple dimensions using mirrors, the system achieves an extended optical path length for high-resolution measurements without linearly increasing the physical space and environmental exposure, thus maintaining measurement resolution while limiting sensitivity to environmental factors
3Object-affected harmful factors
If compact interferometer configuration is used to reduce optical path length, then sensitivity to environmental variations is reduced, but measurement range is limited
Solution Approach 1:
The compact interferometer configuration is enhanced by nesting multiple optical path folds within the same physical space. The mirrors enable the light to traverse the compact space repeatedly, effectively extending the measurement range while maintaining the compact physical footprint that limits environmental sensitivity
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 configuration maintains a relatively small optical path length, reducing sensitivity to environmental variations and allowing for accurate position measurement with minimal influence from moving ranges in other directions.
Implementation Method 1
the reference beam is formed by reflection of the input radiation from a reflective element
Implementation Method 2
the measurement beam is formed by diffraction of the input radiation from the grating on the object
Implementation Method 3
each interferometer is configured to form a reference beam and a measurement beam from an input radiation and to combine the reference beam and the measurement beam to provide output radiation to be delivered to a detector
Data Source
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AI summary
The invention relates to a position measurement system to measure a position of an object relative to a reference, comprising two interferometers, wherein each interferometer is configured to form a reference beam and a measurement beam from input radiation and to combine the reference beam and the measurement beam to provide output radiation to be delivered to a detector, wherein each interferometer is configured such that the reference beam is formed by reflection of input radiation from a reflective element, and such that the measurement beam is formed by diffraction of input radiation from a grating on the object, and wherein the reference beam and the measurement beam are parallel to each other.