Rotary Shaft Sensor With Dual Magnetic Periodicities for Angular Accuracy
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Solution Overview
Problem
Existing sensor devices for determining the relative angular position between shaft halves of a rotary shaft face challenges such as non-ideal arrangements leading to signal distortions, susceptibility to external fields, and long-term stability issues, limiting accuracy and robustness, especially in applications requiring precise angular measurements of 1° to 2° or below.
Innovation Solution
A sensor device comprising two magnetic structures with different spatial magnetic periodicities and at least four stationary sensors detects the superposed magnetic field to determine the relative angular position, using an electronic evaluation circuit to process the sensor signals, allowing for compact design and high accuracy, while being resistant to noise and external fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional sensor devices use a single magnetic structure with fixed periodicity, then the device structure is simple, but the measurement precision is insufficient for small angular ranges (1° to 2° or below)
Solution Approach 1:
The magnetic structure is segmented into multiple magnetic structures (first magnetic structure with first periodicity, second magnetic structure with second periodicity) that generate magnetic fields with different spatial periodicities. This segmentation allows the sensor to resolve small angular positions by combining information from multiple periodicities, achieving high precision measurement of 1° to 2° or below while maintaining manageable device complexity through modular design
Solution Approach 2:
The patent introduces an additional dimension of measurement by using magnetic structures with different periodicities rather than relying on a single periodicity. This multi-periodicity approach creates a more informative measurement space that enables precise determination of small angular positions, effectively adding a dimensional aspect to the measurement process
2Measurement precision
If sensors are arranged in non-ideal positions due to manufacturing tolerances, then the device is easier to manufacture, but signal distortions occur leading to inaccurate position determination
Solution Approach 1:
The evaluation circuit performs self-calibration by determining calibration values from signals obtained at multiple calibration positions, then uses these calibration values to correct subsequent measurements. This self-service approach compensates for non-ideal sensor arrangements and manufacturing tolerances, maintaining high measurement precision without requiring extremely precise manufacturing
Solution Approach 2:
The system performs preliminary calibration by measuring signals at multiple predetermined calibration positions before actual operation. This preliminary action establishes calibration values that account for manufacturing variations and non-ideal arrangements, enabling accurate measurements during normal operation without requiring perfect initial positioning
3Measurement precision
If the sensor device uses multiple magnetic structures with different periodicities and multiple sensors, then the measurement accuracy increases, but the device complexity and number of components increase
Solution Approach 1:
Multiple magnetic structures with different periodicities serve universal measurement functions rather than specialized functions. The first magnetic structure with first periodicity and the second magnetic structure with second periodicity both contribute to angular position measurement, with their combined signals enabling high-resolution determination of small angles. This multi-functionality approach achieves high precision without proportionally increasing device complexity
Solution Approach 2:
The patent merges the measurement functions of multiple magnetic structures and multiple sensors into a unified evaluation process. The evaluation circuit combines signals from sensors detecting different magnetic field components and processes them together to determine angular position. This merging approach achieves high measurement precision while managing device complexity through integrated signal processing
4Adaptability or versatility
If the sensor device is designed for compact size to fit small-scale applications, then the adaptability improves, but the susceptibility to external fields and noise increases
Solution Approach 1:
The evaluation circuit uses feedback mechanisms to distinguish useful magnetic field signals from external fields and noise. By processing signals from multiple sensors and multiple magnetic structures with different periodicities, the system can identify and reject external interference, maintaining measurement accuracy in compact configurations where shielding is limited
Solution Approach 2:
Different magnetic structures are positioned at different locations with different periodicities, creating local variations in the magnetic field measurement. This local quality differentiation allows the system to identify and reject external fields that would uniformly affect all sensors, thereby reducing susceptibility to noise and external interference while maintaining compact size
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 high operational robustness, long-term stability, and accurate measurement results with fault detection capabilities, enabling precise angular position determination and torque measurement in small-scale applications like e-bike cranksets.
Implementation Method 1
respective magnetic fields generated and/or influenced by the first and second magnetic structures superpose
Data Source
Figure 1~2
Figure 3
Figure 4~7
AI summary
The invention describes a sensor device (1) and a method (11, 15) for determining a relative angular position (Δϕ) between a first shaft half (2) and a second shaft half (3) of a rotary shaft, in particular a rotary motor drive shaft, the sensor device (1) comprising: - a first magnetic structure (4) and a second magnetic structure (5) having spatially different magnetic periodicities, wherein the first magnetic structure (4) is mounted on the first shaft half (2) and the second magnetic structure (5) is mounted on the second shaft half (3) such that respective magnetic fields generated and/or influenced by the first and second magnetic structures (4, 5) superpose, - at least four sensors (HE1, HE2, HE3, HE4) mounted stationary with respect to a rotary movement (6) of the rotary shaft such that the superposed magnetic field generated and/or influenced by the first and second magnetic structures (4, 5) is detectable by each of the at least four stationary sensors (HE1, HE2, HE3, HE4), and - an electronic evaluation circuit (7) configured to receive measurement values (q) corresponding to the detected superposed magnetic field from each of the at least four sensors (HE1, HE2, HE3, HE4) in order to determine the relative angular position (Δϕ) from the received measurement values (q) of the at least four sensors (HE1, HE2, HE3, HE4). The rotary shaft may comprise a torsion section (8) elastically interconnecting the two shaft halves (2, 3) for torque transmission.