Rotary Encoder Tracks Prevent Retroreflected Light Interference
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Solution Overview
Problem
Optical type rotary encoders face detection precision deterioration due to retro reflected light at non-transmitting parts, especially when these parts have non-periodic patterns, which existing signal processing systems cannot correct, leading to reduced accuracy in rotational angle detection.
Innovation Solution
A rotary encoder design featuring a rotary disk with alternating light transmitting and non-transmitting parts, where non-transmitting parts have projecting surfaces that retroreflect light back to the light emitting part, and the tracks are arranged such that further reflected light from non-periodic tracks does not enter periodic tracks, preventing signal superposition and improving detection precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If V-grooves are used to form non-transmitting parts, then manufacturing cost is reduced and ease of manufacture is improved, but retro reflected light enters other optical tracks causing detection precision to deteriorate
Solution Approach 1:
The patent applies dimensional separation by arranging tracks in the radial direction at specific positions. The first non-periodic track is positioned at a radius different from the periodic track, and the second non-periodic track is positioned at yet another radius. This radial dimensionality change ensures that retro reflected light from non-periodic tracks cannot enter periodic tracks, solving the precision deterioration problem while maintaining the cost-effective V-groove structure.
Solution Approach 2:
The patent segments the optical tracks into distinct radial zones. By placing the periodic track and multiple non-periodic tracks at different radial positions, it creates spatial segmentation that prevents interference between tracks. This segmentation allows each track type to function independently without retro reflected light contamination from other tracks.
2Measurement precision
If signal processing correction is applied, then periodic error in detection precision is improved, but non-periodic error from retro reflected light cannot be corrected
Solution Approach 1:
The patent converts the harmful retro reflected light into a beneficial spatial separation problem. Instead of trying to correct the interference signal processing-wise, it uses the radial position arrangement to prevent the harmful light from reaching periodic tracks in the first place. The non-periodic tracks' retro reflected light is directed to different radial zones where it cannot interfere with periodic track detection.
3Adaptability or versatility
If multiple optical tracks are arranged concentrically, then the rotary disk can provide comprehensive detection capability, but retro reflected light from one track can enter another track causing signal superposition
Solution Approach 1:
The patent uses radial dimensionality to resolve the conflict between comprehensive detection capability and signal interference. By arranging tracks at different radial distances from the rotation axis, it maintains the concentric multi-track configuration for comprehensive detection while adding radial separation to prevent retro reflected light from entering adjacent tracks.
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 suppresses the deterioration of detection precision caused by retro reflected light, enhancing the accuracy of rotational angle measurement by ensuring that retroreflected light does not interfere with the periodic tracks, and allows for cost-effective production using plastic materials.
Implementation Method 1
a light emitting diode, a rotary disk which is provided with a plurality of optical tracks for converting emitted light from the light emitting diode to modulated light
Implementation Method 2
a light receiving element which receives the modulated light from the rotary disk and converts it to an electrical signal
Implementation Method 3
each of the plurality of non-transmitting parts has a pair of reflecting surfaces which retro reflect incident light to the rotary disk toward the light emitting part
Data Source
AI summary
In a rotary encoder of the present invention, each track of a rotary disk has transmitting parts and non-transmitting parts alternately arranged in the circumferential direction. Each non-transmitting part has a plurality of projecting parts which are arranged side by side in the circumferential direction. Each projecting part has a pair of reflecting surfaces which retro reflect incident light toward a light emitting part. A plurality of tracks include a periodic track where transmitting parts and non-transmitting parts are arranged with a periodic pattern and non-periodic tracks where transmitting parts and non-transmitting parts are arranged in a non-periodic pattern. The periodic track and non-periodic track are respectively arranged at positions in the radial direction where further reflected light at the light emitting part after retro reflection at the reflecting surfaces of the non-periodic track will not enter the periodic track.