Optical Rotary Encoder Using Polarization Difference Imaging
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Solution Overview
Problem
Optical rotary encoders face challenges in manufacturing complexity and cost due to the need for increased etching complexity to enhance accuracy, particularly in incremental and absolute encoder types, and they suffer from loss of positional information when power is lost.
Innovation Solution
The use of polarization difference imaging techniques with a polarizer disk and polarization sensing means, including a polarizer and image sensing structure, to measure angular position, reducing the need for complex etched patterns and allowing for accurate orientation information without a large number of sensors or light sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of etched lines is increased to enhance accuracy in incremental encoders, then measurement precision is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical etched line pattern system with a polarization-based optical system. Instead of using physical etched lines on a disk to encode position information, the invention uses polarized light and polarization sensors to detect angular position. This substitution eliminates the need for complex etching processes while maintaining measurement accuracy through the polarization state of light.
Solution Approach 2:
The patent changes the physical parameter used for encoding from geometric patterns (etched lines) to optical polarization properties. By using polarized light and measuring changes in polarization state rather than light intensity variations from etched patterns, the system achieves accuracy without increased manufacturing complexity. The polarization angle serves as the encoding parameter instead of line density.
2Measurement precision
If the number of sensors and light sources is increased to provide absolute positional information, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent makes the polarization sensing means multi-functional by enabling it to detect both incremental position changes and absolute position information through a single sensor system. The same polarization sensor that detects light polarization changes for incremental measurement also provides reference point detection for absolute positioning, eliminating the need for separate sensor systems for each function.
Solution Approach 2:
The patent uses a virtual copy of the encoder disk pattern in the polarization domain rather than physical etched lines. The polarization state of light creates an optical copy of the position information that can be read by the sensor, providing absolute positional information without requiring additional physical sensors or light sources. The polarization pattern acts as an information copy that enables absolute positioning.
3Measurement precision
If a reference point is added to provide absolute angular position, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces the mechanical reference point (physical marker on the disk) with a polarization-based reference mechanism. Instead of using a physical reference mark that requires additional etching and sensing, the system uses polarization state changes to provide reference information. The polarization reference is embedded in the optical path rather than being a separate mechanical feature.
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 approach simplifies the manufacturing of optical rotary encoders, reduces production costs, and maintains accurate angular position measurement without the need for complex etched disks, while also preserving positional information even when power is lost.
Implementation Method 1
a polarizer disk fixed to the rotatable member and interposed between the light source and the polarization sensing means
Implementation Method 2
The measured intensity is amplified or fed into a comparator to produce a sign wave or digital square wave
Data Source
AI summary
An optical rotary encoder uses polarization difference imaging techniques to calculate an angle of orientation of a rotatable member. The optical rotary encoder includes a light source, a polarization sensor that has a polarizer and image sensing structure, and a polarizer disk fixed between to the rotatable and interposed between the light source and the polarization sensor.