Optical Rotary Angle Sensor for Electric Power Steering
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Solution Overview
Problem
Current optical rotary angle sensors for electric power assisted steering systems are expensive and require a counter to store the revolution number, limiting their effectiveness and simplicity.
Innovation Solution
A compact and inexpensive optical rotary angle sensor using a light source, optical components, and a disc with an optical pattern that encodes a binary type code, allowing for relative rotation and interference-based intensity modulation to determine the disc's position and angle, eliminating the need for a revolution counter and providing absolute steering angle measurement at startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current optical steering angle sensors use image sensors or multiple light sources, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex image sensors and multiple light sources with a simple single light source and photodetector system. The optical encoder disc with radial and circumferential patterns encodes position information optically, eliminating the need for complex mechanical or electronic imaging systems while maintaining high measurement precision through interference-based detection
Solution Approach 2:
The patent uses changes in optical parameters (light intensity, phase, and interference patterns) to encode steering angle information. The radial and circumferential patterns on the encoder disc create specific interference patterns that are detected by the photodetector, allowing precise angle measurement through optical parameter variations rather than complex sensor arrays
2Measurement precision
If optical sensors use multiple light sources and image sensors, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent employs inexpensive components including a single light source (LED or laser), a simple photodetector, and an optical encoder disc that can be manufactured using standard machining or molding techniques. This approach dramatically reduces manufacturing cost compared to image sensors or multiple light source systems while maintaining sufficient measurement precision through the encoded optical patterns
Solution Approach 2:
The patent uses an optical encoder disc with radial and circumferential patterns that creates optical copies of position information through light reflection and interference. The patterns on the disc encode angular position data that is read optically, providing a low-cost alternative to expensive electronic sensors while maintaining measurement accuracy
3Measurement precision
If rotor position sensors use a counter to store revolution number, then absolute position measurement is improved, but device complexity increases
Solution Approach 1:
The patent pre-encodes absolute position information directly into the optical patterns on the encoder disc before operation. The radial and circumferential patterns are manufactured in specific configurations that represent absolute angular positions, eliminating the need for runtime counting or storage operations. The system reads pre-encoded position data directly through optical interference, providing absolute measurement without memory requirements
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
The solution provides a high-resolution, cost-effective optical rotary angle sensor that can measure absolute steering angles without a storage unit, ensuring accurate readings over multiple turns and low-resolution startup signals, enhancing the electric power assisted steering system's performance.
Implementation Method 1
light reflected from the optical pattern is measured by the photodetector
Implementation Method 2
light reflected by steps and spaces destructively interferes leading to an intensity modulation of the reflected light
Data Source
AI summary
A rotary angle sensor for an electric power assisted steering system of a motor vehicle, wherein the rotary angle sensor comprises an optical sensor unit with a light source, optical components and a photodetector and a disc with an optical pattern, wherein the optical sensor unit and the disc are configured to rotate relative to each other around a rotary axis, and wherein the optical sensor unit is configured such that light reflected from the optical pattern is measured by the photodetector, wherein the optical pattern comprises steps and spaces separating the steps, such that light reflected by steps and spaces destructively interferes leading to an intensity modulation of the reflected light according to an optical pattern which encodes a binary type code for the rotary angle of the disc.