Rotary Optical Encoder with Yawed Grating Bars and Structured Illumination
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Solution Overview
Problem
Existing optical encoders face challenges in maintaining accurate displacement measurements due to scale defects or contamination, as current methods either disable the encoder or provide error signals, but do not effectively mitigate errors without complex signal processing.
Innovation Solution
A contamination and defect-resistant rotary optical encoder configuration that uses a structured illumination generating arrangement and a detector arrangement with spatial phase detectors to provide displacement signals, which are resistant to contaminants and defects by employing a crossover beam configuration and a set of spatial phase detectors arranged in a specific sequence to detect and compensate for errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional optical encoder configurations are used, then the encoder can provide displacement measurements, but the measurements become inaccurate when scale defects or contamination are present
Solution Approach 1:
The invention divides the optical measurement function into multiple independent measurement channels, each with its own light source and detector. By segmenting the illumination into multiple beams that traverse different paths across the scale, the system can identify and exclude measurements affected by localized defects or contamination, thereby maintaining overall measurement accuracy and reliability
Solution Approach 2:
The invention introduces an intermediary processing system that receives signals from multiple measurement channels and applies logic to identify abnormal readings caused by defects or contamination. This intermediary layer filters out erroneous measurements before they affect the final displacement output, protecting the measurement system from the harmful effects of scale imperfections
2Measurement precision
If complex signal processing methods are used to mitigate errors from defects or contamination, then measurement accuracy can be maintained, but the device complexity increases
Solution Approach 1:
Instead of using complex signal processing on a single measurement channel, the invention segments the measurement into multiple independent channels with simpler individual processing. Each channel provides basic displacement data, and the combination of multiple simple measurements achieves the error mitigation that would otherwise require complex processing of a single channel
Solution Approach 2:
The invention creates multiple copies of the measurement system (multiple light sources and detectors) that independently measure the same displacement. By having redundant copies that can be compared and validated against each other, the system achieves error detection and correction through simple comparison logic rather than complex signal processing
3Reliability
If multiple measurement channels are used to resist contaminants and defects, then reliability improves, but the device complexity increases
Solution Approach 1:
The invention designs the multiple measurement channels to be universal and identical in structure, each performing the same measurement function. This universality allows the system to achieve enhanced reliability through redundancy while keeping individual channel complexity low, as each channel is a standardized, simple unit that can be easily replicated and integrated
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 allows for accurate displacement measurements despite contaminants or defects, without the need for complex signal processing, by using a crossover beam configuration and spatial phase detectors to detect and compensate for errors, ensuring robustness and reliability.
Implementation Method 1
a first scale grating that is configured to input incident light and diffract the incident light
Implementation Method 2
a second scale grating that is configured to input the diffracted light and interfere with the diffracted light to form a moiré pattern
Data Source
AI summary
An optical encoder configuration comprises a cylindrical or planar rotary scale including yawed grating bars, an illumination source, a structured illumination generating arrangement (SIGA) and a detector arrangement including a photodetector. The SIGA is configured to input source light to a first illumination region on the rotary scale which diffracts light to a beam deflector configuration which transmits the diffracted light in a form that provides a particular fringe pattern proximate to a second illumination region on the scale. The scale filters and outputs that light to form a detector fringe pattern of intensity bands that are long along the rotary measuring direction and relatively narrow and periodic along a detected fringe motion direction (DFMD) transverse to the rotary measuring direction. The photodetector is configured to detect a position of the intensity bands as a function of rotary scale displacement and provide corresponding displacement or position signals.