Absolute Angle Encoder Using Co-Prime Radii to Extend Measurement Range
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Solution Overview
Problem
Existing absolute angle measurement devices, such as rotary encoders, are limited to measuring angles up to 360° and cannot provide unambiguous absolute angle measurements beyond this range without relying on memory to store counter values, making them unsuitable for applications requiring greater angle measurements.
Innovation Solution
A device comprising two rotatable members with specific radii and detectable elements, where the products of the number of detectable elements and radii are co-prime, allowing for absolute angle measurement beyond 360° by using sensors and a processor to calculate the Bézout numbers and determine the absolute angle without storing counter values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a memory is provided to store counter values for measuring angles greater than 360°, then the measurement range is extended, but the device complexity increases
Solution Approach 1:
The patent transitions from a one-dimensional single-ring encoder to a two-dimensional system with two concentric rings having different radii. This dimensional expansion allows the system to encode absolute position information beyond 360° by combining phase differences from both rings, eliminating the need for memory storage while extending the measurement range.
Solution Approach 2:
The patent changes the physical parameters of the encoder system by introducing two rings with radii in a specific irrational ratio (e.g., √2:1). This parameter change creates a mathematical relationship where the combined phase measurements from both rings can uniquely determine absolute positions over multiple revolutions without requiring memory to store counter values.
2Measurement precision
If two concentric rings with magnets and Hall sensors are used to determine absolute rotation angle, then the measurement capability is improved, but the device becomes incapable of measuring angles greater than 360°
Solution Approach 1:
The patent adds a second dimensional layer by introducing another concentric ring with a different radius. The combination of phase differences from both rings creates a mathematical system that can resolve absolute positions beyond a single 360° rotation, effectively adding a temporal dimension to the measurement capability.
Solution Approach 2:
The patent creates a composite encoder system by combining two rings with different physical characteristics (radii in irrational ratio) and detectable elements. This composite structure leverages the mathematical properties of irrational ratios to generate unique phase difference patterns that encode absolute position information over multiple revolutions.
3Measurement precision
If optical encoders are used with light sources and photo detectors, then the detection capability is improved, but the device becomes unsuitable for bearing applications where grease may obscure the rings
Solution Approach 1:
The patent replaces the optical detection system (light sources and photo detectors) with a magnetic detection system using Hall sensors and magnets. This substitution eliminates the vulnerability to grease obscuration while maintaining the ability to detect rotational position, making the device suitable for bearing applications.
Solution Approach 2:
The patent introduces magnetic fields as an intermediary between the rotating rings and the sensors. Instead of using light (which can be obscured by grease), the system uses magnetic fields from magnets attached to the rings, which can be detected by Hall sensors without being affected by grease contamination in bearing environments.
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
Enables unambiguous absolute angle measurement beyond 360° without the need for memory storage, suitable for applications like bearings, by using co-prime products of parameters to determine the absolute angle through sensor detection and processor calculations.
Implementation Method 1
In optical shaft encoders, the openings or alternating transparent and opaque areas may be detected using a light source and a photo detector
Implementation Method 2
Magnetic shaft encoders typically use a ring provided with a plurality of magnets and Hall sensors capable of detecting the magnets as the ring rotates
Data Source
AI summary
A device for measuring an absolute angle includes first and second rotatable members having first and second radii and capable of rotating over first and second angles respectively, a first number of detectable elements mounted on the first rotatable member, a second number of detectable elements mounted on the second rotatable member, and at least one sensor for detecting rotation of the detectable elements. The second rotatable member is coupled with the first rotatable member such that the second angle is equal to the first angle times the ratio of the first radius and the second radius. The first radius is equal to a first integer times a factor, while the second radius is equal to a second integer times the factor. The product of the first number and the second integer, and the product of the second number and the first integer, are co-prime.