Optical Rotary Encoder Using Focused Laser Beam Array
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Solution Overview
Problem
Conventional optical rotary encoders face limitations in achieving high optical resolution due to low light utilization efficiency, complex manufacturing processes, and interference between diffraction orders, especially when the required angular resolution is high, leading to small code regions on the code disk that are difficult to manufacture and align accurately.
Innovation Solution
The optical rotary encoder employs a laser source unit, a focusing unit with a microlens array or multiple-beam grating, and a photodetector array to form multiple light points on concentric code tracks of the code disk, enhancing optical resolution by reducing energy loss and interference through coherent light and precise beam shaping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional light emitting diodes are used as light source with periodic grating segmentation on code disk, then the encoder can provide basic angular resolution, but the optical resolution is limited and cannot achieve high precision when code region area becomes very small
Solution Approach 1:
The patent segments the single laser beam into multiple focused beams using a beam splitting element, with each beam targeting a specific code track on the code disk. This segmentation allows simultaneous reading of multiple code tracks, effectively increasing the measurable angular resolution without requiring proportionally smaller code region areas on each track.
Solution Approach 2:
The patent transitions from conventional planar illumination to three-dimensional focused beam configuration by using a microlens array or beam splitting element to create multiple focal points at different radial positions on the code disk. This dimensional transformation enables high resolution measurement while maintaining adequate code region areas through spatial distribution of measurement points.
2Measurement precision
If the code disk has high angular resolution with many code tracks, then positioning accuracy improves, but the code region area for each track becomes very small making manufacturing and alignment difficult
Solution Approach 1:
The measurement function is segmented across multiple code tracks, with each track read by a dedicated focused beam. This allows the system to achieve high positioning accuracy through combined data from multiple tracks, while each individual track can maintain larger, easier-to-manufacture code regions compared to a single high-density track design.
Solution Approach 2:
The patent changes the optical parameters by using focused beams with specific focal lengths and aperture sizes, allowing the system to resolve smaller features optically without requiring proportionally smaller physical code regions. This parameter optimization enables manufacturing-friendly code region sizes while achieving high measurement precision.
3Device complexity
If a single laser beam covers multiple code tracks simultaneously, then the device complexity is reduced, but interference between diffraction orders occurs and light utilization efficiency decreases
Solution Approach 1:
The patent segments the broad illumination beam into multiple narrow focused beams, each directed at a specific code track. This segmentation eliminates cross-track interference and diffraction order mixing that occur with broad illumination, significantly improving light utilization efficiency. The added complexity of beam splitting elements is offset by the removal of interference-related losses.
Solution Approach 2:
The patent introduces a beam splitting element (microlens array or diffraction grating) as an intermediary that transforms a single broad beam into multiple focused beams. This intermediary component enables efficient light distribution to multiple code tracks while preventing direct interference between beams, effectively mediating between the simplicity of single-beam illumination and the efficiency of multi-beam targeted illumination.
4Measurement precision
If the code region area is reduced to achieve higher bits, then angular resolution increases, but the code disk resembles a grating that induces optical diffraction and interferes with signal rays
Solution Approach 1:
The patent uses focused beams that illuminate only the specific code track region needed for measurement, rather than broad illumination covering the entire code disk. This partial action approach ensures that even when code regions are small, the focused beam energy is concentrated on the target area, minimizing diffraction effects and interference while maintaining high angular resolution.
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 significantly improves optical resolution by reducing interference and energy loss, allowing for higher precision in motor control systems, such as in machine tools and self-driving cars, while simplifying manufacturing and alignment processes.
Implementation Method 1
a laser source unit configured to emit a laser beam
Implementation Method 2
a focusing unit configured to convert the laser beam into a light pattern having a plurality of light points respectively on a plurality of code tracks that are concentric
Implementation Method 3
the code disk modulates the incident laser beams to form optical code signals
Implementation Method 4
a photodetector array including a plurality of photodetectors configured to convert the optical code signals into electric code signals
Data Source
AI summary
An optical rotary encoder includes a code disk, a laser source unit, a focusing unit and a photodetector array. The focusing unit converts the laser beam emitted by the laser source unit into incident laser beams that have a plurality of light points respectively on code tracks of the code disk, such that the code disk modulates the incident laser beams to form optical code signals. The photodetector array receives and converts the optical code signals into electric code signals.