Heterodyne Grating Measurement via Segmented Single Diffraction
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Solution Overview
Problem
Existing grating displacement measuring systems face challenges in achieving high optical subdivision without increasing complexity, as secondary diffraction or multiple diffraction methods are sensitive to grating surface accuracy and attitude errors, affecting measurement accuracy.
Innovation Solution
A heterodyne one-dimensional grating measuring device using two linearly polarized lights with overlapping, orthogonal polarization and fixed frequency difference, generating +1-order and -1-order diffracted lights, which are processed to achieve four-fold optical subdivision through a simple and compact reading head structure, reducing the impact of grating surface accuracy and attitude errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If secondary diffraction or multiple diffraction is adopted to achieve four-fold or higher optical subdivision, then the optical subdivision is improved, but the system complexity increases and measurement accuracy is affected by grating surface accuracy and attitude errors
Solution Approach 1:
The patent segments the optical measurement process into two independent single-diffraction channels: a measurement light path and a reference light path. Each channel performs single diffraction independently, avoiding the complexity of secondary or multiple diffraction while achieving four-fold optical subdivision through heterodyne interference between the two channels. This segmentation resolves the contradiction by maintaining simple optical structures while achieving high optical subdivision.
Solution Approach 2:
The patent introduces a frequency-shifting intermediary mechanism (acousto-optic modulator or electro-optic modulator) that assigns different frequencies to the measurement light and reference light before they undergo single diffraction. This frequency difference serves as an intermediary that enables heterodyne detection, allowing the system to achieve four-fold optical subdivision through interference without requiring complex secondary diffraction structures.
2Measurement precision
If secondary diffraction or multiple diffraction is used to achieve higher optical subdivision, then the optical subdivision is improved, but the measurement accuracy deteriorates due to sensitivity to grating surface accuracy and attitude errors
Solution Approach 1:
By segmenting the measurement into two separate single-diffraction channels (measurement path and reference path), the patent eliminates the accumulation of errors that occurs in secondary or multiple diffraction systems. Each channel independently performs single diffraction, which is less sensitive to grating surface accuracy and attitude errors, thereby improving measurement reliability while achieving four-fold optical subdivision through heterodyne interference.
Solution Approach 2:
The patent implements a feedback mechanism where the reference light path (undergoing single diffraction) provides a stable reference signal that is heterodyne-interfered with the measurement light path. This feedback approach allows real-time compensation and correction, improving measurement accuracy by抵消ing the effects of grating surface errors and attitude variations without requiring complex multiple diffraction structures.
3Device complexity
If conventional single diffraction is used to achieve two-fold optical subdivision, then the system structure remains simple, but the optical subdivision is limited and cannot achieve four-fold or higher
Solution Approach 1:
The patent merges two single-diffraction channels (measurement light path and reference light path) into a heterodyne interference system. By combining the outputs of two simple single-diffraction processes with a frequency difference, the system achieves four-fold optical subdivision without the complexity of secondary diffraction structures. This merging approach resolves the contradiction by maintaining structural simplicity while achieving higher optical subdivision.
Solution Approach 2:
The patent changes the frequency parameter of the light beams by introducing a frequency shift between the measurement light and reference light using acousto-optic or electro-optic modulators. This parameter change enables heterodyne detection, allowing the system to achieve four-fold optical subdivision through interference of two single-diffraction channels without increasing structural complexity.
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 solution enables four-fold optical subdivision with improved measurement accuracy and reduced system complexity, while maintaining a simple and lightweight structure, allowing for further combinations with secondary diffraction to enhance optical subdivision.
Implementation Method 1
a light source configured to generate two beams of linearly polarized lights having characteristics of overlapping, polarization orthogonal, and fixed frequency difference
Implementation Method 2
One path is a beat frequency signal having a frequency of fB-fA where the beat frequency having the frequency of fB-fA is formed by interfering the second polarized light component of the -1-order diffracted light with the first polarized light component of the +1-order diffracted light
Implementation Method 3
the first polarized light and the second polarized light are respectively incident on a surface of a moving one-dimensional measuring grating to generate a +1-order diffracted light and a -1-order diffracted light
Data Source
AI summary
A heterodyne one-dimensional grating measuring device and measuring method thereof, including a light source, a reading head, a photoelectric receiving module, and a signal processing system. The light source is configured to generate two linearly polarized lights having characteristics of overlapping, polarization orthogonal, and fixed frequency difference. The reading head is configured to receive two beams of polarized lights and be respectively incident on a surface of a moving measuring grating to generate a +1-order diffracted light and a −1-order diffracted light. The photoelectric receiving module is configured to receive the +1-order diffracted light and the −1-order diffracted light to form two paths of beat frequency signals. The signal processing system is configured to perform differential calculation on the two paths of the beat frequency signals to realize a displacement measurement of single diffraction of the measuring grating for four-fold optical subdivision.