Optical Encoder Index Photodiode Width Variation
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Solution Overview
Problem
Optical rotation encoders face issues with total harmonic distortion and optical magnification mismatch in differential quadrature signals, leading to error index signals in position detection.
Innovation Solution
The optical encoder employs a photodiode array with multiple sets of position photodiodes and index photodiodes, where the position photodiodes at the ends are partially covered by an opaque layer to alleviate harmonic distortion, and the index photodiodes are strategically sized and positioned to mitigate magnification mismatch effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If differential quadrature signals are used for position detection, then position detection capability is provided, but total harmonic distortion occurs in the signals
Solution Approach 1:
The patent applies local quality by making the index photodiodes have a different width (second width) compared to the position photodiodes (first width). Specifically, the index photodiodes are positioned at the ends of the photodiode array and have a width optimized for their specific function of detecting index marks, while position photodiodes have widths optimized for position detection. This local differentiation reduces total harmonic distortion in the differential quadrature signals while maintaining position detection capability.
2Measurement precision
If index photodiodes are used to confirm absolute position, then absolute position detection is enabled, but error index signals are generated due to optical magnification mismatch
Solution Approach 1:
The patent positions index photodiodes specifically at the two ends of the photodiode array, separated from the position photodiodes. This spatial separation and specialized positioning allows index photodiodes to detect index marks with optimized performance, reducing optical magnification mismatch effects and eliminating error index signals while maintaining absolute position detection capability.
3Measurement precision
If photodiode array is configured with multiple sets of position photodiodes, then position detection resolution is improved, but device complexity increases
Solution Approach 1:
The patent segments the photodiode array into distinct functional zones: position photodiodes for position detection and index photodiodes for index mark detection. By dividing the array into these specialized segments with different widths and positions, the system achieves high position detection resolution while managing complexity through functional specialization rather than uniform configuration.
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 effectively reduces total harmonic distortion and eliminates error index signals, improving the accuracy of position detection in optical encoders by ensuring proper alignment and matching of optical image profiles with photodiode dimensions.
Implementation Method 1
The photodiode array receives modulated light from the code disk to output differential quadrature signals
Data Source
AI summary
There is provided an optical encoder including a photodiode array and a code disk opposite to each other. The photodiode array includes at least three sets of position photodiodes and two index photodiodes arranged transversally. The two index photodiodes are adjacently arranged at the same side of the at least three sets of position photodiodes. A first set of position photodiodes and a last set of position photodiodes of the at least three sets of position photodiodes are partially covered to alleviate the total harmonic distortion. The rest position photodiodes of the at least three sets of position photodiodes other than the first and last sets of position photodiodes are not covered.