Orthogonal Diffraction Grating Displacement Measurement
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Solution Overview
Problem
Existing displacement measurement devices using optical interference face a limitation where the detection range narrows as the distance between diffraction gratings increases, due to the attenuation of interference light amplitude with increasing optical path difference.
Innovation Solution
A displacement measurement device and method that measure relative displacements of diffraction gratings in a direction orthogonal to the optical axis, eliminating optical path differences between diffracted light, thereby maintaining interference light amplitude regardless of grating distance, using a configuration with a light source, first and second diffraction gratings, and an optical sensor detecting interference between ±nth order diffracted light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the distance between diffraction gratings is increased, then the measurement range is extended, but the amplitude of interference light decreases due to increased optical path difference
Solution Approach 1:
The patent changes the measurement direction from the optical axis direction to a direction orthogonal to the optical axis. This parameter change in measurement orientation eliminates the optical path difference effect while preserving the ability to measure displacement over extended ranges.
Solution Approach 2:
The patent transitions from measuring displacement along the optical axis (one dimension) to measuring displacement in a direction orthogonal to the optical axis (another dimension). This dimensional change allows the system to avoid the optical path difference problem while maintaining measurement capability.
2Adaptability or versatility
If the distance between diffraction gratings is increased, then the detection range should expand, but the detection range narrows due to interference light attenuation
Solution Approach 1:
The patent changes the measurement orientation parameter from parallel to optical axis to orthogonal to optical axis. This parameter change resolves the contradiction by eliminating the optical path difference mechanism that causes detection range narrowing, thereby maintaining both expanded adaptability and reliability.
3Device complexity
If optical interference measurement is performed along the optical axis, then the setup is simple, but the detection range narrows with increasing grating distance
Solution Approach 1:
The patent measures displacement in a direction orthogonal to the optical axis rather than along the optical axis. This dimensional change maintains relatively simple optical system configuration while eliminating the detection range narrowing problem, thus resolving the contradiction between device complexity and adaptability.
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 approach prevents the narrowing of detection range and ensures stable interference light amplitude, enabling precise measurement of displacements across a wider range without amplitude reduction, even as the distance between diffraction gratings changes.
Implementation Method 1
The optical sensor detects interference between diffracted light (first-order diffracted light, for example) diffracted by the first diffraction grating and diffracted light (first-order diffracted light, for example) produced when the second diffraction grating diffracts the zero-order light that passes directly through the first diffraction grating
Implementation Method 2
a first diffraction grating and a second diffraction grating that are arranged along a progression path of light from the light source and that are movable relative to one another, the first diffraction grating and the second diffraction grating generating diffracted light
Data Source
AI summary
A displacement measurement device includes: a light source; a first diffraction grating and a second diffraction grating arranged along a path of light from the light source and movable relative to one another, the first and second diffraction gratings generating diffracted light; an optical sensor that detects interference light produced by interference between −nth order diffracted light generated as a result of the second diffraction grating diffracting +nth order diffracted light from the first diffraction grating and +nth order diffracted light generated as a result of the second diffraction grating diffracting −nth order diffracted light from the first diffraction grating, where n is a natural number greater than or equal to 1; and a calculation unit calculating, according to a signal from the optical sensor, a relative displacement between the first and second diffraction gratings in a direction orthogonal to an optical axis of the first and second diffraction gratings.