Encoder Scale Grating Segmentation for Harmonic Distortion
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Solution Overview
Problem
Existing encoders face challenges in stably restraining harmonic distortion and precisely detecting position due to increased diffractive influence from the scale grating to the index grating, and existing solutions do not effectively reduce harmonic components across varying optical gaps.
Innovation Solution
The encoder design incorporates a scale with a pattern of alternating reflective and non-reflective sections, where the reflective sections have different widths and opening ratios in the Y direction, allowing the photodetector array to receive light and process signals that minimize harmonic distortion by equally weighting diffracted images from sections with different grating opening ratios, thereby reducing the amplitude of harmonic components irrespective of the optical gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the aperture width of the scale grating is converted into a 2/3 pitch to remove harmonic distortion, then the third harmonic component is reduced, but the diffractive influence increases and harmonic components are less likely to reduce
Solution Approach 1:
The scale grating is divided into multiple divided sections (first, second, third sections) along the Y direction, each with different opening ratios. This segmentation allows the diffracted images from different sections to be equally weighted, stabilizing harmonic distortion reduction across varying optical gaps.
Solution Approach 2:
Different divided sections of the scale grating are assigned different opening ratios (first section: 2/3, second section: 1/3, third section: 2/3). This local variation in opening ratios ensures that harmonic components are reduced stably regardless of optical gap changes, as the photodetector receives equally weighted signals from sections with different grating characteristics.
2Length of stationary object
If the optical gap between scale grating and index grating is increased, then the diffractive influence increases, but harmonic components are less likely to reduce
Solution Approach 1:
The opening ratios of the divided sections are specifically designed with different values (2/3, 1/3, 2/3) to compensate for diffractive effects. This parameter optimization ensures that even when the optical gap increases, the harmonic components remain reduced because the photodetector equally weights the diffracted images from sections with different opening ratios.
3Device complexity
If a conventional single opening ratio grating is used, then the structure is simple, but harmonic distortion cannot be stably restrained across varying optical gaps
Solution Approach 1:
The scale grating is segmented into multiple divided sections with different opening ratios arranged along the Y direction. This segmentation, while increasing structural complexity, enables stable harmonic distortion reduction across varying optical gaps, thereby improving position detection reliability.
Solution Approach 2:
The scale grating functions as a composite structure with multiple sections having different opening ratios (2/3, 1/3, 2/3). This composite design allows the system to maintain stable harmonic distortion reduction performance across different optical gaps, achieving both complexity and reliability.
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 design effectively stabilizes harmonic distortion reduction and enhances position detection precision across a wide range of optical gaps, ensuring accurate position measurement by minimizing the impact of harmonic components on the signal.
Implementation Method 1
as the diffractive influence increases in the propagation from the scale grating to the index grating
Implementation Method 2
A scale (20) that includes a plurality of unit block patterns (KA) arranged in a position measuring direction (X) with a period of a pitch. A pattern (24A) of the unit block pattern has a symmetrical shape with respect to a symmetry line (Xc) perpendicular to the position measuring direction
Data Source
Figure 1
Figure 2A~2B
Figure 3~4B
AI summary
An encoder includes a scale (20) that includes a plurality of unit block patterns (KA) arranged in a position measuring direction (X) with a period of a pitch. A pattern (24A) of the unit block pattern has a symmetrical shape with respect to a symmetry line (Xc) perpendicular to the position measuring direction. Each unit block pattern includes a plurality of divided sections along a direction (Y) perpendicular to the position measuring direction. An area ratio of the pattern which is a value made by dividing an area of the pattern in each divided section by an area of the divided section is different between two adjacent divided sections. The pattern in each divided section has a rectangular shape defined by two parallel lines that extend in the position measuring direction and two parallel lines that extend in the direction perpendicular to the position measuring direction.