Optical Encoder Radial Grating Segmentation for Noise Reduction
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Solution Overview
Problem
Conventional optical encoders face challenges in achieving high-resolution angle measurement with low noise, especially when the diameter is downsized, as they struggle to improve signal efficiency and reduce noise components effectively.
Innovation Solution
The optical encoder incorporates a rotary scale with a grating pattern featuring first and second patterns extending radially, where the light receiving element detects interference fringes formed by both patterns, and is configured to satisfy specific relations between the periods of these patterns to enhance light utilization efficiency and signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the detection radius is small, then the encoder can be downsized, but the noise increases and signal efficiency cannot be improved
Solution Approach 1:
The rotary scale is divided into multiple radial regions (first radial region, second radial region, third radial region) with different grating patterns. Each region has a specific period (P1, P2, P3) designed to optimize light contribution at different distances from the reading center, allowing the encoder to effectively utilize light from across the entire scale surface even when downsized.
Solution Approach 2:
Different radial regions of the rotary scale are assigned different grating periods tailored to their specific distances from the reading center. The first pattern (period P1) is optimized for the first radial region, the second pattern (period P2) for the second radial region, and the third pattern (period P3) for the third radial region. This local optimization ensures that light from each region contributes effectively to the detection signal, maintaining high signal-to-noise ratio even in compact encoders.
2Use of energy by moving object
If light beam from grating pattern in region that cannot substantially contribute to detection signals is condensed on light receiving surface, then light receiving efficiency is improved, but noise components are increased
Solution Approach 1:
The grating period parameter is changed across different radial regions of the rotary scale. By adjusting the period (P1, P2, P3) according to the radial distance from the reading center, the optical path and interference conditions are optimized for each region. This ensures that light from all regions contributes constructively to the detection signal with appropriate intensity, maximizing light receiving efficiency while preventing noise from regions that would otherwise contribute insignificantly or destructively.
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 light utilization efficiency and signal-to-noise ratio, enabling effective detection of light beams that previously did not contribute to signals, even when the diameter is reduced, thereby achieving high-resolution angle measurement with low noise.
Implementation Method 1
a light receiving element which detects interference fringes of the grating pattern irradiated with the light from the light source
Implementation Method 2
a light receiving element which detects interference fringes of the grating pattern irradiated with the light from the light source, wherein the light receiving element is disposed to receive a first interference fringe having a period Q1 formed by the first pattern and to receive a second interference fringe having a period Q2 which is diffracted by the second pattern
Data Source
AI summary
In order to provide an optical encoder with high resolution, the optical encoder includes: a rotary scale provided with a grating pattern having a first radial pattern and a plurality of concentric circular patterns disposed at predetermined intervals; and a light receiving element which detects a first interference fringe formed by the first pattern having a first period in the circumferential direction, a second interference fringe which is diffracted in a direction of the first interference fringe by a grating pattern having a second period in the circumferential direction disposed at a different radial position so that the second interference fringe has a period closer to the first period than the second period.