Five-DOF Heterodyne Grating Interferometry System
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Solution Overview
Problem
Current interferometry systems, particularly laser interferometry systems, are limited to single-degree-of-freedom displacement measurement and face accuracy issues due to geometric installation errors, thermal drift, and environmental factors, making them inadequate for multi-degree-of-freedom precision measurements required in advanced industrial applications.
Innovation Solution
A five-degree-of-freedom heterodyne grating interferometry system is developed, featuring a single-frequency laser, acousto-optic modulator, interferometer lens group, measurement grating, and optical fiber bundles, which enables simultaneous measurement of two linear displacements and three rotational angles with high accuracy by using a compensation interference signal to mitigate thermal drift and optical fiber transmission errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If distributed combination of multiple single-degree-of-freedom laser measurement systems is used to achieve multi-degree-of-freedom measurement, then measurement capability is improved, but system structure becomes complicated and optical debugging becomes difficult
Solution Approach 1:
The patent combines multiple single-degree-of-freedom measurement capabilities into a single integrated heterodyne grating interferometry system. By merging the reference light path and measurement light path into one coherent optical system with a unified laser source, the system achieves multi-degree-of-freedom measurement (displacement and rotational angle) while maintaining a compact and simple structure, avoiding the complexity of distributed combinations.
Solution Approach 2:
The interferometry system is designed with universal functionality to measure multiple parameters simultaneously. The optical system can perform displacement measurement along the optical axis, displacement measurement perpendicular to the optical axis, and rotational angle measurement around the optical axis, all within a single system that uses a common laser source and optical path.
2Measurement precision
If conventional laser interferometry systems are used for displacement measurement, then measurement capability is achieved, but measurement accuracy decreases due to geometric installation errors, thermal drift errors, and periodic nonlinear errors
Solution Approach 1:
The system employs feedback mechanisms through the heterodyne detection method, where the frequency difference between reference and measurement light paths allows for real-time error detection and correction. The phase modulation and demodulation processes provide feedback that compensates for thermal drift and periodic nonlinear errors, maintaining high measurement accuracy.
Solution Approach 2:
The patent utilizes parameter changes in the optical frequency domain through heterodyne modulation. By modulating the frequency of the measurement light relative to the reference light using acoustic waves, the system transforms static measurement into dynamic frequency-based measurement, which is inherently more resistant to environmental disturbances and geometric errors.
3Measurement precision
If existing multi-degree-of-freedom measurement systems are used, then measurement capability is achieved, but rotational angle measurement accuracy is only arcsecond order and displacement measurement accuracy is micrometer order, rarely reaching nanometer level
Solution Approach 1:
The system replaces traditional mechanical angle encoders and displacement sensors with an optical heterodyne interferometry system. This substitution eliminates mechanical errors and achieves higher accuracy through optical phase measurement, reaching nanometer-level displacement accuracy and microradian-level rotational angle accuracy.
Solution Approach 2:
The system uses periodic acoustic wave modulation to create frequency-shifted reference and measurement beams. This periodic modulation enables precise phase measurement through heterodyne detection, achieving consistent high-accuracy measurements by converting physical displacements and angles into measurable frequency and phase differences.
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 system achieves nanometer-level accuracy for linear displacements and microradian-level accuracy for rotational angles, providing a compact, high-precision measurement solution that is less susceptible to environmental factors and capable of compensating for errors, suitable for applications like precision machine tools and semiconductor detection equipment.
Implementation Method 1
a single-frequency laser device and an acousto-optic modulator, wherein the single-frequency laser device emits a single-frequency laser, which is then incident on the acousto-optic modulator
Implementation Method 2
an interferometer lens group and a measurement grating, which are used to form the reference light and the measurement light into a measurement interference signal and a compensation interference signal
Implementation Method 3
a plurality of optical fiber bundles which receive the measurement interference signal and the compensation interference signal respectively
Data Source
AI summary
A five-degree-of-freedom heterodyne grating interferometry system, comprising a single frequency laser device (1) and an acousto-optic modulator (2); the single frequency laser device (1) emits a single frequency laser, and the single frequency laser is coupled by optical fiber and, after being split, enters the acousto-optic modulator (2) to obtain two linearly polarized lights of different frequencies, one being a reference light, and one being a measurement light; an interferometer lens group (3) and a measurement grating (4), used for forming the reference light and the measurement light into a measurement interference signal and a compensation interference signal; and multiple optical fiber bundles (5), respectively receiving the measurement interference signal and the compensation interference signal, each optical fiber bundle (5) having multiple multimode optical fibers respectively receiving signals at different positions on the same plane. The present measurement system has the advantages of high measurement precision, a large measurement range, not being sensitive to temperature drift, and small overall size, and can be used as a photoetching machine ultra-precision workpiece table position measurement system.