Irregular Diffraction Grating for Encoder Signal Harmonic Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In encoder systems, higher diffraction orders interfere with the generation of interference fringes, particularly when the Talbot number is low, leading to unwanted harmonics and signal distortion, especially in compact designs with close optical components and larger diffraction feature periods.
Innovation Solution
The diffraction features are arranged such that their spacing varies irregularly, allowing selective control of diffraction orders to minimize or eliminate higher odd orders while maintaining the 1st and selected odd orders, thereby reducing harmonics and improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the Talbot number is low (compact design with close optical components), then the device size is reduced, but higher diffraction orders interfere with interference fringe generation causing signal distortion
Solution Approach 1:
The patent applies local quality by making the spacing between adjacent diffraction features non-uniform across the grating structure. Specifically, the spacing varies depending on the position of the diffraction features, allowing selective suppression of higher diffraction orders while maintaining the desired first-order diffraction for interference fringe generation. This localized variation in spacing creates position-dependent diffraction characteristics that eliminate harmful harmonics without compromising the overall device compactness.
2Reliability
If the spacing between diffraction features is made non-uniform, then higher diffraction orders are suppressed, but the manufacturing complexity increases
Solution Approach 1:
The patent implements parameter changes by systematically varying the spacing parameter between adjacent diffraction features according to a defined pattern or function. Rather than creating truly random or complex non-uniform spacing, the invention uses controlled parameter variation where the spacing follows a specific mathematical relationship or gradient. This approach enables the suppression of higher diffraction orders while maintaining manufacturability through predictable, systematic structure fabrication.
3Ease of manufacture
If equidistant diffraction features are used, then the grating is easy to manufacture, but unwanted harmonics are generated in the displacement signal
Solution Approach 1:
The patent applies asymmetry by deliberately breaking the uniform spacing symmetry of traditional diffraction gratings. Instead of equidistant features that produce symmetric diffraction patterns with harmful harmonics, the invention introduces asymmetric spacing variations between adjacent features. This asymmetric configuration selectively suppresses higher-order diffraction components that cause harmonic distortion in the displacement signal, while preserving the primary diffraction orders needed for accurate measurement.
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 arrangement significantly reduces the intensity of higher diffraction orders, achieving a superior signal output with a higher ratio of 1st to 5th or 7th order intensity, resulting in a harmonic-free signal and improved positional measurement accuracy.
Implementation Method 1
an array of diffraction features arranged such that the spacing between the centres of adjacent diffraction features varies from one pair of adjacent diffraction features to the next
Data Source
Figure 1~2a
Figure 2b
Figure 3~4
AI summary
An optical element for generating diffraction orders for an encoder apparatus, in which the optical element comprises an array of diffraction features arranged such that the spacing between the centres of adjacent diffraction features varies irregularly from one pair of adjacent features to the next.