Optical Encoder Crosstalk Reduction via Wavelength Selection
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Solution Overview
Problem
Existing optical encoders suffer from crosstalk issues due to light emitted from one light source entering the opposing light receiving arrays, which degrades light detecting accuracy and limits the ability to downsize the device.
Innovation Solution
The optical encoder employs light-emitting elements that emit light of different wavelengths to displacement-measuring optical gratings, with corresponding photo detectors designed to receive only the predetermined wavelength, and includes filters to shield other wavelengths, and light-collimating members to prevent light scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If photo detectors are disposed close to each other to downsize the optical encoder, then the size of the optical encoder is reduced, but crosstalk occurs where light from one light source enters the opposing light receiving array, degrading measurement accuracy
Solution Approach 1:
The patent applies wavelength selection as a parameter change to resolve the crosstalk issue. Each light-emitting element emits light at a specific wavelength, and corresponding photo detectors are configured to detect only that wavelength. This wavelength-based parameter differentiation allows photo detectors to be disposed close together without crosstalk, as each detector responds only to its designated wavelength. The patent states: 'the light-emitting element emits light having a different wavelength to the respective optical gratings provided on the main scale... the photo detectors receive the light having the predetermined wavelength that has been transmitted through or reflected by the respective optical gratings'
Solution Approach 2:
The patent introduces wavelength-specific optical filters as intermediary elements between the light sources and photo detectors. These filters act as mediators that selectively transmit only the desired wavelength to the corresponding photo detector while blocking other wavelengths. This intermediary mechanism prevents crosstalk even when photo detectors are in close proximity, enabling both compact size and high measurement accuracy
2Measurement precision
If light-emitting elements emit different wavelengths to different optical gratings, then crosstalk is prevented and measurement accuracy is improved, but the device complexity increases due to wavelength-specific filters and detectors
Solution Approach 1:
The patent makes the photo detectors universal by designing them to respond to specific wavelengths through selective filtering rather than requiring completely separate detection systems for each wavelength. The same photo detector structure can be used across multiple channels, with wavelength selectivity achieved through optical filters rather than different detector types. This multi-functional approach reduces overall system complexity while maintaining crosstalk prevention
Solution Approach 2:
The patent manages device complexity by standardizing the optical components while varying only the wavelength parameter. All light-emitting elements and photo detectors use the same basic structure, with differentiation achieved through wavelength-specific filters and emission characteristics. This parameter-based approach allows for mass production of standardized components, reducing manufacturing and system integration complexity despite the multi-wavelength requirement
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 solution effectively prevents crosstalk, allowing photo detectors to be placed closer together, enhancing measurement accuracy and enabling a more compact optical encoder design.
Implementation Method 1
at least one light-emitting element that emits light respectively to the optical gratings provided on the main scale
Implementation Method 2
the photo detectors receive the light transmitted through or reflected by the optical gratings
Implementation Method 3
a filter may be provided on an optical path of the light from the light-emitting element to the photo detectors, the filter transmitting light that is emitted from the light-emitting element and is provided with a predetermined wavelength while shielding light having a wavelength other than the predetermined wavelength
Implementation Method 4
a light-collimating member for collimating the light emitted from the light source
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An optical encoder (100) is provided with: a light-emitting element (30) including a main-signal light-emitting element (31) having a red LED (31 A) that emits red light and an origin light-emitting element (32) having an infrared LED (32A) that emits infrared light; and a receiver unit (40) including a main-signal photo detector (41) that receives the red light to generate a predetermined signal and an origin photo detector (42) that receives the infrared light to generate a predetermined signal. Accordingly, even when the infrared light enters the main-signal photo detector (41) or the red light enters the origin photo detector (42), no signal is generated by the light, thereby effectively preventing crosstalk. Thus, the measurement accuracy of the optical encoder (100) can be improved.