Phase Grating Bar-Gap Ratio for Vernier Signal Accuracy
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Solution Overview
Problem
Existing optical position measuring devices face challenges in achieving an improved signal-to-noise ratio for vernier fringe patterns, which affects measuring accuracy due to the interaction of periodic light patterns with measuring graduations having a 1:1 bar-gap ratio and insufficient suppression of the zeroth diffraction order.
Innovation Solution
An optical position measuring device with a phase grating measuring graduation that deviates from a 1:1 bar-gap ratio, where the phase shift between bars and gaps is designed to suppress the zeroth diffraction order, ensuring that higher diffraction orders are deflected and strike bright areas of the vernier pattern, increasing light intensity and signal accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a 1:1 bar-gap ratio measuring scale is used, then the device structure is simple, but the signal-to-noise ratio of the vernier pattern is insufficient
Solution Approach 1:
The patent changes the bar-gap ratio parameter from the conventional 1:1 to a non-1:1 ratio (specifically 1:2 or 2:1), which fundamentally alters the diffraction characteristics of the measuring scale. This parameter change enables selective suppression of the zeroth diffraction order while enhancing higher orders, thereby improving the signal-to-noise ratio of the vernier pattern without complicating the overall device structure.
2Device complexity
If the zeroth diffraction order is not suppressed, then the light transmission is simple, but the measurement accuracy is reduced due to noise
Solution Approach 1:
The patent converts the potentially harmful zeroth diffraction order (which causes noise and reduces measurement accuracy) into a beneficial effect by using the non-1:1 bar-gap ratio to selectively suppress it. The suppression mechanism transforms what would be a noise source into a controlled element, enhancing the signal quality of the vernier pattern and improving measurement accuracy.
3Device complexity
If the light intensity in the vernier pattern is low, then the optical system is simple, but the usable signal is insufficient for accurate measurement
Solution Approach 1:
The patent changes the diffraction parameters by using a non-1:1 bar-gap ratio, which fundamentally alters the light distribution in the vernier pattern. This parameter change concentrates the light energy into higher diffraction orders while suppressing the zeroth order, thereby increasing the usable signal intensity without adding complex optical components.
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 enhances the signal-to-noise ratio of the vernier pattern, leading to improved measuring accuracy by increasing the intensity of light areas and effectively suppressing the zeroth diffraction order, thereby enhancing the overall performance of the position measuring device.
Implementation Method 1
The measuring scale is a phase grating whose bar-to-gap ratio deviates from 1:1 and whose phase shift between bars and gaps is configured to suppress the zeroth diffraction order. Furthermore, the position measuring device is designed such that at the position where the zeroth diffraction order of a bright area of the incident light pattern is suppressed, at least one higher diffraction order is deflected and hits one of the bright areas of the vernier pattern on the detector arrangement.
Implementation Method 2
The interaction of a periodic light pattern with a periodic measuring scale generates a Vernier fringe pattern in a subsequent detection plane.
Data Source
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AI summary
The invention relates to an optical position measuring device for measuring the relative position of two objects. A vernier pattern with bright and dark areas is generated by the interaction of a measuring grating (10) with a light pattern (M) on a detector arrangement (21). The measuring grating is a phase grating configured with respect to the incident light pattern (M) such that the intensity of the bright areas of the vernier pattern is maximized by the interaction of geometric ray optics and wave optics.