Slanted Code Slits and Photodiodes for Low-Distortion Optical Encoders
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Solution Overview
Problem
Optical encoding systems suffer from total harmonic distortion in photocurrents, leading to degraded positioning accuracy and error signals due to imperfect 90-degree phase shift and optical magnification mismatch.
Innovation Solution
The arrangement of slanted code slits and photodiodes relative to the radial direction of the code disk reduces total harmonic distortion by altering the orientation of code slits and photodiodes, ensuring precise alignment and reducing harmonic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If code slits are arranged radially on the code disk, then the structure is simple and easy to manufacture, but total harmonic distortion occurs degrading positioning accuracy
Solution Approach 1:
The code slits are arranged at a slant angle relative to the radial direction, creating an asymmetric configuration. This asymmetric arrangement disrupts the harmonic distortion patterns that occur with purely radial slits, thereby reducing total harmonic distortion while maintaining positioning accuracy.
Solution Approach 2:
The orientation parameter of the code slits is changed from purely radial (0 degrees relative to radial direction) to a slanted configuration (non-zero angle relative to radial direction). This parameter change modifies the optical interference pattern and reduces harmonic distortion components in the photocurrent signal.
2Measurement precision
If photodiodes are arranged perpendicular to the radial direction, then the alignment is simple, but phase shift is not exactly 90 degrees causing positioning errors
Solution Approach 1:
The photodiodes are arranged at a slant angle relative to the radial direction rather than being perfectly perpendicular. This asymmetric arrangement creates the necessary phase shift conditions for accurate positioning while maintaining manufacturing feasibility through a systematic slanting approach.
Solution Approach 2:
The orientation parameter of the photodiodes is adjusted from a fixed perpendicular arrangement to a slanted configuration. This parameter modification optimizes the phase shift between adjacent photodiodes to achieve closer to 90-degree phase relationships, improving positioning accuracy.
3Reliability
If code slits have uniform length and radial orientation, then manufacturing is easy, but optical magnification mismatch generates error index signals
Solution Approach 1:
The code slits are configured with a slant angle relative to the radial direction, creating an asymmetric pattern that compensates for optical magnification variations. This asymmetric design reduces the generation of error index signals by balancing the optical path lengths more effectively.
Solution Approach 2:
The slanted configuration of code slits creates locally optimized optical paths that account for magnification variations at different radial positions. This local quality adjustment ensures more uniform optical response across the photodiode array, reducing error signals.
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 approach significantly reduces total harmonic distortion from 3.63% to 0.122%, enhancing positioning accuracy and minimizing error signals in optical encoding systems.
Implementation Method 1
The optical rotation encoder includes a code disk and a photodiode array. The photodiode array receives modulated light from the code disk to output differential quadrature signals
Data Source
AI summary
There is provided an optical encoding system including a photodiode array and a code disk opposite to each other. The code disk is arranged with multiple code slits at a ring area corresponding to the photodiode array. A length direction of each photodiode of the photodiode array has at least one deviation angle with respect to a length direction of the multiple code slits to reduce the total harmonic distortion in photocurrents.