Heterodyne Grating Interferometer for Sub-Nanometer Displacement
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Solution Overview
Problem
Current dual-frequency laser interferometer systems used in ultra-precision workpiece tables for lithography machines face challenges such as environmental sensitivity, difficulty in improving measurement speed, space occupation, high cost, and limited precision, particularly in achieving sub-nanometer resolution for large-stroke horizontal and vertical displacement measurements.
Innovation Solution
A heterodyne grating interferometer system utilizing a dual-frequency laser generator, interferometer, and photo-electric conversion units to produce beat frequency signals, enabling sub-nanometer resolution and precision in measuring large-stroke horizontal and vertical displacements, with a compact and lightweight design that reduces system disturbance and enhances dynamic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dual-frequency laser interferometer is used to measure displacement, then measurement precision can be achieved, but environmental sensitivity increases and measurement speed cannot be improved
Solution Approach 1:
The patent replaces the traditional dual-frequency laser interferometer with a grating-based measurement system that uses diffraction and interference principles. The grating measurement system achieves displacement measurement through optical path difference changes caused by grating displacement, thereby reducing environmental sensitivity while maintaining measurement precision.
Solution Approach 2:
The patent changes the measurement principle from dual-frequency laser interferometry to grating-based diffraction and interference. By using a grating with specific groove densities and wavelengths, the system achieves sub-nanometer measurement precision while being less sensitive to environmental factors such as temperature and humidity changes.
2Measurement precision
If a dual-frequency laser interferometer is used, then measurement precision is achieved, but measurement speed cannot be improved and space is occupied
Solution Approach 1:
The patent substitutes the dual-frequency laser interferometer with a grating measurement system that utilizes diffraction and interference principles. This replacement enables faster measurement speeds while maintaining sub-nanometer precision, as the grating system can process displacement information more rapidly without the speed limitations of traditional interferometers.
3Measurement precision
If a dual-frequency laser interferometer is used, then measurement precision is achieved, but system cost and complexity increase
Solution Approach 1:
The patent replaces the complex dual-frequency laser interferometer system with a grating-based measurement system. The grating system uses simpler optical components and diffraction principles to achieve the same measurement precision, thereby reducing system complexity and cost while maintaining sub-nanometer measurement capability.
4Adaptability or versatility
If a single-frequency two-dimensional grating measurement system is used, then horizontal and vertical displacement measurements are achieved, but measurement precision is reduced due to signal susceptibility to disturbances
Solution Approach 1:
The patent changes the laser frequency parameter from single-frequency to dual-frequency, which significantly improves the signal's resistance to disturbances. The dual-frequency laser generates beat frequencies that are less susceptible to environmental noise and disturbances, thereby maintaining high measurement precision while achieving both horizontal and vertical displacement measurements.
Solution Approach 2:
The patent introduces a dual-frequency laser as an intermediary element that generates beat frequencies serving as the measurement signal. This intermediary signal is more robust against disturbances compared to single-frequency signals, enabling precise multi-directional displacement measurements in the presence of environmental noise and interference.
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
The heterodyne grating interferometer system achieves sub-nanometer resolution and precision, reduces system size and weight, and improves the dynamic performance of ultra-precision workpiece tables, addressing the limitations of existing systems while meeting stringent measurement demands.
Implementation Method 1
a dual-frequency laser generator (11) comprising a laser tube (111), a first polarization beam splitter (112), an acousto-optic modulator
Implementation Method 2
a dual-frequency laser generator (11) comprising a laser tube (111)
Implementation Method 3
an interferometer (12)
Implementation Method 4
a measurement grating (2)... based on the moire principle and the diffraction and interference principle
Implementation Method 5
The measuring principle of the grating measurement system is mainly based on the moire principle
Implementation Method 6
a reference signal photo-electric conversion unit (13) and a measurement signal photo-electric conversion unit (14)
Data Source
AI summary
A displacement measurement system of heterodyne grating interferometer, comprises a reading head, a measurement grating and an electronic signal processing component. Laser light emitted from the laser tube is collimated, passes through the first polarization spectroscope, and then emits two light beams with an orthogonal polarization direction and an orthogonal propagation direction; the two light beams pass through two acousto-optic modulators and respectively generate two first-order diffraction light beams with different frequencies, which are later divided into reference light and measurement light; two parallel reference light beams form a beat frequency electric signal with positive and negative first-order diffraction measurement light respectively after passing through a measurement signal photo-electric conversion unit; the beat frequency signals are transmitted to the electronic signal processing component for signal processing, thus the output of linear displacement in two directions is realized.