Optical Encoder Readhead Phosphor Wavelength Conversion
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Solution Overview
Problem
Existing optical encoders face limitations in achieving high resolution due to poor signal-to-noise ratios and restricted design alternatives, particularly when using self-imaging or interferometric techniques, which are affected by the operating gap, light source wavelength, and photodetector response, leading to limited displacement or position signal interpolation and reduced reliability.
Innovation Solution
The use of a light source with a short wavelength (300-450 nm) and a photodetector with a peak response at a longer wavelength, combined with a phosphor layer and spatial phase detectors, to enhance the signal-to-noise ratio and achieve higher resolution by converting the initial wavelength to a more efficiently detectable second wavelength, allowing for a larger operating gap and improved tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a short wavelength light source (300-450 nm) is used to provide a large operating gap, then the operating gap and tolerance are improved, but the photodetector response becomes poor resulting in a poor signal-to-noise ratio
Solution Approach 1:
A phosphor layer is introduced as an intermediary between the short wavelength light source and the photodetector. The phosphor layer absorbs the short wavelength light (300-450 nm) and converts it to longer wavelength light that matches the photodetector's peak response, thereby mediating the wavelength mismatch and simultaneously achieving both a large operating gap and high signal-to-noise ratio
Solution Approach 2:
The invention changes the wavelength parameter of the light detected by the photodetector through the phosphor conversion process. By transforming the short wavelength light into longer wavelength light that aligns with the photodetector's spectral response peak, the system optimizes both the operating gap and signal quality
2Measurement precision
If a fine scale grating pitch is used to achieve high resolution, then the measurement resolution is improved, but the operating gap tolerance decreases and reliability is reduced
Solution Approach 1:
By changing the light wavelength parameter to short wavelengths (300-450 nm), the self-imaging arrangement enables a larger operating gap while maintaining the fine scale grating pitch, thereby improving both resolution and reliability simultaneously
3Length of stationary object
If conventional photodetectors are used with short wavelength light, then the operating gap can be increased, but the photodetector response is poor limiting signal interpolation
Solution Approach 1:
The phosphor layer serves as a wavelength conversion intermediary that transforms short wavelength light into longer wavelength light matching the photodetector's peak response, thereby enabling both large operating gap and high signal interpolation capability
Solution Approach 2:
The system changes the effective detected wavelength parameter through phosphor conversion, aligning the photodetector's operational wavelength with its peak response wavelength to maximize signal quality and interpolation capability
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 improves measurement resolution by approximately 30% and increases the operating gap, providing higher reliability and repeatability while maintaining a high signal-to-noise ratio, even with fine grating pitches, by effectively overcoming the limitations of prior art encoders.
Implementation Method 1
a phosphor layer positioned to receive light arising from the periodic intensity pattern at the first wavelength and output second wavelength light
Data Source
AI summary
A device for measuring relative displacement between two members includes a scale grating and an optical encoder readhead comprising a first wavelength light source illuminating the grating. The grating outputs scale light to form a moving periodic intensity pattern at the first wavelength. The readhead comprises a plurality of spatial phase detectors comprising: a periodic spatial filter; a phosphor layer that receives light arising from the first wavelength periodic intensity pattern and outputs second wavelength light, and a photodetector element that receives, and is sensitive to, the second wavelength light. The photodetector element inputs second wavelength light corresponding to a spatially filtered version of the first wavelength periodic intensity pattern and outputs a signal indicative of its spatial phase relative to that spatial phase detector. The spatial filtering may be provided by a mask element, or by a pattern of the phosphor layer and/or the detector element, in various embodiments.