Optical Encoder Light Propagation Control for Stray Light Reduction
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Solution Overview
Problem
Conventional optical encoders face challenges with size reduction, leading to increased stray light and noise due to smaller detecting head dimensions, which affects signal-to-noise ratio and reliability, and the use of resin molding introduces issues with thermal expansion and potential circuit wire breaks.
Innovation Solution
An optical encoder design featuring a light transmitting member with a light propagation controlling pattern on its surface, which controls light reflection and transmission to reduce stray light and noise, while maintaining a thin and compact structure, and using a mold resin with a plane parallel plate to improve accuracy and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the thickness of the transparent optical member is reduced to achieve size reduction, then the encoder becomes thinner and more compact, but light reflected at the inner surface enters the photoelectric conversion elements causing signal deterioration
Solution Approach 1:
The patent converts the harmful reflected light into a beneficial effect by intentionally designing the inner surface of the transparent optical member with a specific reflectance (5-20%). This controlled reflection creates an optical path that guides light from the light emitting element through the scale to the photoelectric conversion elements, enabling the thin encoder structure to function properly while maintaining signal quality.
Solution Approach 2:
The patent changes the optical parameter (reflectance) of the transparent optical member's inner surface from the conventional low reflectance (≤10%) to a specific range (5-20%). This parameter change allows the thin optical member to control light propagation effectively, reducing stray light while maintaining the necessary optical path for signal detection.
2Length of stationary object
If the distance between light emitting section and light receiving section is reduced to achieve smaller head size, then the encoder becomes more compact, but stray light inside the head increases causing noise
Solution Approach 1:
The patent converts stray light, which is normally a harmful factor, into a useful optical path. By setting the inner surface reflectance to 5-20%, reflected light that would otherwise be stray light is redirected through the scale and onto the photoelectric conversion elements, contributing to the detection signal rather than creating noise.
Solution Approach 2:
The transparent optical member's inner surface acts as an intermediary that controls light propagation. By adjusting its reflectance to 5-20%, it mediates between the light emitting element and the photoelectric conversion elements, guiding light through the scale while preventing direct stray light from reaching the detectors without proper optical path control.
3Length of stationary object
If resin molding is used for packaging to achieve size reduction, then the encoder becomes more compact, but thermal expansion causes circuit wire breaks
Solution Approach 1:
The patent changes the material parameter of the packaging from conventional metal or ceramics to resin molding material with specific thermal expansion characteristics. This allows the packaging to accommodate thermal expansion differences and reduce stress on circuit wires while maintaining the compact encoder structure.
Solution Approach 2:
The patent uses composite material construction where the transparent optical member and packaging are made of resin materials that can be molded together. This composite approach allows for integrated design that accommodates thermal expansion while maintaining structural integrity and compact size.
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
The solution effectively reduces stray light and noise, enhances signal-to-noise ratio, allows for smaller and thinner encoders, and improves reliability by minimizing thermal expansion issues, enabling stable and accurate position detection.
Implementation Method 1
a light emitting section which emits light
Implementation Method 2
a light receiving section which receives the light and converts the light into an electrical signal
Implementation Method 3
light which emerges from the light emitting section will be reflected at an inner surface of the transparent optical member
Data Source
AI summary
An optical encoder includes a scale, and a detecting head which is disposed facing the scale. The scale is provided with a grating which has a predetermined optical pattern with respect to a direction of relative movement, and the detecting head is provided with a light emitting section which irradiates predetermined light to the scale, and a light detecting section which detects a movement of a pattern of light distribution formed on a light receiving surface of a photodetector, by light reflected by the grating upon being irradiated to the scale from the light emitting section. A light transmitting member is disposed on a surface of the light emitting section and the photodetector of the detecting head, toward the scale, and a light propagation controlling pattern for controlling propagation of light is disposed on a surface of the light transmitting member, facing the scale.