Multi-faceted flat-faced lens for optical encoder stray light reduction
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Solution Overview
Problem
Reflective optical encoders suffer from low contrast, low resolution, and high manufacturing costs due to issues like stray light, poor light collimation, and limited encoding capabilities, which restrict their operational speed and performance.
Innovation Solution
A reflective optical encoder design featuring a multi-faceted lens with flat faces, an optically transparent material, and a light barrier to minimize stray light, combined with diffractive optical elements for enhanced light collimation, is used to direct and refract light efficiently towards a code scale, improving contrast and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a reflective optical encoder uses a conventional dome lens, then the profile is low and assembly is simplified, but light collimation is poor leading to low contrast and low resolution
Solution Approach 1:
The lens is divided into multiple flat facets instead of using a single curved dome surface. Each facet is angled to direct light from the LED toward the code scale, creating multiple collimated beams that improve contrast and resolution while maintaining a low profile design
Solution Approach 2:
The patent replaces the conventional curved dome lens with flat-planar facets. This flat-faced design eliminates the need for complex spherical or aspherical curving processes, simplifying manufacturing while achieving superior light collimation through precise angular positioning of each facet
2Length of stationary object
If a reflective optical encoder places the light emitter and light detector on the same substrate, then the profile is reduced and assembly is simplified, but stray light from the emitter directly hits the detector causing contrast degradation
Solution Approach 1:
The patent extracts or removes the harmful stray light paths by designing the multi-faceted lens to direct light precisely toward the code scale and reflect it back to the detector, while the flat facets inherently block direct line-of-sight stray light between the emitter and detector on the same substrate
Solution Approach 2:
Each facet of the multi-faceted lens is locally optimized with specific angular orientations to direct light from the LED through the code scale to the detector. This local angular precision ensures that only useful reflected light reaches the detector while stray light is blocked, maintaining high contrast in a low-profile design
3Measurement precision
If a reflective optical encoder uses a conventional lens, then manufacturing is simpler, but light collimation is poor limiting encoder performance and resolution
Solution Approach 1:
The lens is segmented into multiple flat facets that can be manufactured using simpler processes such as precision cutting or molding of flat surfaces, avoiding the need for complex spherical lens grinding and curving. Each facet is angled to achieve proper light collimation, combining manufacturing simplicity with high resolution performance
Solution Approach 2:
The patent eliminates curved lens surfaces entirely in favor of flat-planar facets. This removes the need for complex spherical or aspherical lens fabrication processes, allowing the lens to be manufactured using simpler flat-surface techniques while achieving superior light collimation through precise angular positioning of each facet
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 enhances the performance of reflective optical encoders by reducing stray light, increasing resolution, and lowering manufacturing costs, enabling higher operational speeds and improved encoding capabilities.
Implementation Method 1
the multi-faceted lens is configured to direct and refract selectively light emitted by the light source
Implementation Method 2
at least a portion of the light reflected from the code scale is directed towards the second face and refracted through portions of the lens for detection by the light detector
Data Source
AI summary
Disclosed are various embodiments of high-speed, high-performance, low-noise, low-cost, compact, optical encoders having a multi-faceted flat-faced lens is disposed over the light emitters and light detectors thereof. Disclosed also are various means for preventing undesired stray light from reaching light detectors incorporated therein. Structures employed to block stray light in the optical encoders include light barriers, air gap trenches, and coatings disposed between first and second sides of a substrate of the encoder. Methods of making such optical encoders are also disclosed.