Amplitude Grating Sealing Layer for Optical Position Measurement
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Solution Overview
Problem
The existing optical position-measuring devices with amplitude gratings suffer from reduced light-dark contrast due to destructive interference and are sensitive to environmental and mechanical influences, which affect the stability and precision of the measurement.
Innovation Solution
A material measure for position-measuring devices is enhanced by adding a sealing layer with the same refractive index as the spacer layer, ensuring a phase shift of 2π for light beams, thus eliminating destructive interference and improving contrast, while protecting the partially transparent layer from environmental influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a partially transparent layer is used to create dark areas through destructive interference, then the scale can be read optically, but the light-dark contrast is reduced due to additional destructive interference at bright areas
Solution Approach 1:
A sealing layer with the same refractive index as the spacer layer is introduced as an intermediary element. This sealing layer compensates for the phase deviation caused by the spacer layer, ensuring that light beams reflected from the mirror layer and directly from the sealing layer interface constructively interfere in bright areas, thereby restoring the light-dark contrast while maintaining optical readability
2Manufacturing precision
If a very thin metal layer is used for the partially transparent layer, then the optical properties can be precisely controlled, but the layer becomes sensitive to chemical and mechanical influences
Solution Approach 1:
A sealing layer is applied as a protective film over the thin metal layer. This sealing layer shields the partially transparent metal layer from chemical and mechanical environmental influences while allowing the precise optical properties of the thin metal layer to be maintained, thus improving reliability without sacrificing manufacturing precision
3Manufacturing precision
If the spacer layer thickness is precisely controlled to achieve π phase deviation, then dark areas can be formed, but production fluctuations affect the stability of the measurement
Solution Approach 1:
The sealing layer is designed with the same refractive index and matched thickness as the spacer layer, creating a symmetric optical structure. This parameter matching ensures that phase deviations caused by production fluctuations in one layer are compensated by the other layer, thereby improving measurement stability while maintaining the ability to form dark areas through controlled interference
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 results in increased light-dark contrast, improved stability, and enhanced precision in signal evaluation, making the device less sensitive to environmental and production-related fluctuations, with a wider process window for layer thickness variations and extended wavelength compatibility.
Implementation Method 1
the optical path lengths (i.e. the products of the refractive index and the layer thickness) for the spacer layer and the sealing layer are each approximately the same or differ by an odd multiple
Implementation Method 2
Light incident on this partially transparent layer is partially reflected and transmitted. The reflected light is extinguished by destructive interference with the transmitted light reflected back from the lower mirror layer
Implementation Method 3
A light beam emitted by the scanning head and reflected in the bright area of the scale on the mirror layer experiences a phase shift of 2π or an integer multiple thereof when it traverses the spacer layer and the sealing layer twice
Implementation Method 4
These light beams therefore no longer interfere destructively as in the prior art, the brightness of the bright area is no longer reduced
Data Source
Figure 1~2
AI summary
A physical measure with an amplitude grating for a position measuring device with optical scanning is described, comprising a carrier (T) on which a mirror layer (S) is arranged, followed by a transparent spacer layer (A) on which a grid-structured, semi-transparent layer (M) is arranged. The semi-transparent layer (M) defines a light-dark pattern, with areas containing the semi-transparent layer (M) appearing dark and areas lacking the semi-transparent layer (M) appearing light. A sealing layer (V) is arranged on the structured, semi-transparent layer (M). The products (nAdA, nvdv) of the refractive index (nA, nv) and the layer thickness (dA, dV) for the spacer layer (A) and the sealing layer (V) are either the same or differ by an odd multiple.