Optical Displacement Measuring Device With Conjugate Imaging
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Solution Overview
Problem
Existing optical displacement measuring devices using diffraction gratings face challenges in detecting position with high resolution due to posture changes and external influences, such as foreign objects on the grating plane, which disrupt the interference signal and make it difficult to maintain stable detection.
Innovation Solution
The optical displacement measuring device configures reflecting optical systems with imaging elements of equal focal lengths and positions the diffraction grating and reflectors around these focal points, ensuring that diffracted beams remain aligned and interfere without shifting, even during posture changes or grating movements perpendicular to the grating plane, thus maintaining a stable interference signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If imaging is performed on the grating plane of the diffraction grating, then the distance between the diffraction grating and the imaging elements is maintained, but the interference signal amplitude fluctuates due to foreign objects on the grating plane
Solution Approach 1:
The patent changes the imaging plane from the grating plane to a position conjugate to the grating plane through the imaging elements. By imaging the diffracted beams at a different spatial location (the image plane rather than the grating plane), the system eliminates the direct influence of foreign objects on the grating surface while maintaining the optical path relationship necessary for stable interference signal detection.
2Measurement precision
If imaging is performed on the grating plane of the diffraction grating, then the optical path length is maintained, but the diffracted beams shift during posture change and the interference signal becomes small
Solution Approach 1:
The patent changes the imaging parameter from imaging the grating plane to imaging the diffracted beam at a conjugate plane. This parameter change allows the optical path length to remain stable while accommodating posture changes of the diffraction grating, preventing beam shift and maintaining interference signal quality for precise position detection.
3Measurement precision
If the diffraction grating moves in a direction perpendicular to the grating plane, then the grating vector direction remains unchanged, but the diffracted beams shift and the interference signal deteriorates
Solution Approach 1:
The imaging elements act as intermediaries that conjugate the grating plane to the image plane. This intermediary optical system allows the diffraction grating to move perpendicular to its plane without directly affecting the interference signal, as the imaging elements compensate for the positional changes and maintain beam alignment for stable interference detection.
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 allows for precise detection of the movement position of a movable portion with high resolution and stability, even when the diffraction grating is inclined or has undulations, by maintaining the optical path alignment and preventing interference signal deterioration.
Implementation Method 1
a diffraction grating configured to move relatively in a direction parallel to a grating vector as to a coherent beam to be irradiated to diffract this coherent beam
Implementation Method 2
cause two two-time beams generated by diffracting two one-time beams through the diffraction grating to interfere with each other
Implementation Method 3
a first imaging element configured to condense a coherent beam emitted from the light emitting unit, and a second imaging element configured to image a two-time diffracted beam
Implementation Method 4
a reflecting optical system configured to reflect each of two one-time diffracted beams generated by diffracting two coherent beams through the diffraction grating
Data Source
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AI summary
An optical displacement measuring device includes a diffraction grating, a reflecting optical system configured to irradiate two one-time diffracted beams diffracted at the diffraction grating on the diffraction grating again, and the reflecting optical system includes a first imaging element, a second imaging element, a first reflector, and a second reflector, wherein the focal length of the first imaging element and the focal length of the second imaging element are the same, the diffraction grating and first reflector are disposed around the focal position of the first imaging element, and the diffraction grating and second reflector are disposed around the focal position of the second imaging element, thereby suppressing influence of displacement of the diffraction grating as to other than a direction where a movement position is detected.