Optical Encoder Light Transmission Member Stray Light Control
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Solution Overview
Problem
Existing optical encoders face challenges in miniaturization and cost reduction due to the complexity of light-emitting and light-receiving elements, with stray light affecting signal-to-noise ratios and making precise displacement detection difficult.
Innovation Solution
The optical encoder design incorporates a light transmission member with a first grating and an aperture, mounted directly on the light-emitting unit, which narrows the light beam and blocks stray light, ensuring that only relevant light reaches the scale and detection unit, thereby improving signal quality and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If light-emitting and light-receiving elements are miniaturized using bare-chip or surface mounting types, then encoder size is reduced, but signal-to-noise ratio deteriorates due to stray light
Solution Approach 1:
A light transmission member with a grating pattern is introduced as an intermediary component between the light-emitting element and the scale. This grating acts as a spatial filter that directs light along a specific optical path, preventing stray light from reaching the light-receiving element while maintaining miniaturization benefits
Solution Approach 2:
The light transmission member is designed with a grating pattern that creates different optical properties in different regions. The grating lines are arranged to allow light transmission only in the desired direction, creating localized light paths that prevent stray light interference while maintaining compact dimensions
2Ease of manufacture
If light-emitting and light-receiving elements are encapsulated in clear mold resin, then manufacturing cost is reduced, but stray light increases affecting detection precision
Solution Approach 1:
The light transmission member with grating pattern serves as a mediator within the resin encapsulation. It maintains the cost benefits of resin sealing while introducing optical control features that prevent stray light generation and transmission, thereby preserving detection precision
Solution Approach 2:
The grating pattern on the light transmission member changes the optical parameters of the system by creating specific refraction and reflection angles. This modifies the light path in a controlled manner, preventing stray light while maintaining the encapsulated structure
3Measurement precision
If aperture is added to narrow light beam, then signal-to-noise ratio is improved, but device complexity increases
Solution Approach 1:
The aperture function is merged with the light transmission member that already contains the grating pattern. By integrating both the grating and aperture features into a single component, the design achieves beam narrowing and stray light rejection without proportionally increasing device complexity
Solution Approach 2:
The light transmission member is designed to perform multiple functions simultaneously: it provides structural support, creates the grating pattern for light direction, and incorporates the aperture for beam narrowing. This multi-functionality reduces the need for separate components, limiting the increase in device complexity
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 enhances the signal-to-noise ratio, allows for stable and precise detection of relative displacement, and facilitates miniaturization while maintaining reliable operation, even in a resin-sealed reflecting type encoder.
Implementation Method 1
the light transmission member has a first grating having an optical pattern of a predetermined pitch
Implementation Method 2
an aperture configured to narrow the light emitted from the light emission unit and impinging on the second grating of the scale
Implementation Method 3
having a second grating that has an optical pattern of a predetermined pitch
Implementation Method 4
the image being formed by the light reflected or diffracted by the second grating of the scale
Implementation Method 5
a light detection unit having light detection elements arranged at a predetermined pitch; a motion of an image on the light detection elements of the light detection unit is detected
Data Source
AI summary
An optical encoder comprises an encoder head and a scale having a second grating that has an optical pattern. The encoder head has a light emission unit to emit specific light to the scale, a light transmission member to transmit the light emitted from the light emission unit and a light detection unit having light detection elements arranged at a predetermined pitch. The light transmission member has a first grating having an optical pattern of a predetermined pitch and an aperture to narrow the light emitted from the light emission unit and impinging on the second grating of the scale. A motion of an image on the light detection elements of the light detection unit is detected. The image is formed by the light reflected or diffracted by the second grating of the scale after the light impinges on the scale through the light transmission member.