Magnetic Rotor Position Sensing Using Vernier Phase Shift
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Solution Overview
Problem
Existing motor control systems face challenges in accurately determining the relative position of the rotor to the stator, especially in brushless DC and reluctance motors, particularly at startup when back electromagnetic force is not available, and traditional methods like block commutation are inefficient.
Innovation Solution
A magnetic sensor system utilizing two magnetic sensors with a back bias magnet to detect changes in the magnetic field interacting with moveable targets, employing the Nonius or Vernier principle to determine the relative position by measuring the unique phase shift between the sensors' signals, with the scale defined by the number of motor pole pairs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional block commutation with three Hall switches is used, then the system is simple to implement, but the measurement precision of rotor position is insufficient for accurate motor synchronization
Solution Approach 1:
The system divides the position measurement function into two separate magnetic sensors, each detecting different magnetic field components. One sensor detects the radial component while the other detects the tangential component, allowing independent measurement of different aspects of rotor position with higher precision than a single Hall switch system
Solution Approach 2:
A back bias magnet is introduced as an intermediary element between the rotor magnets and the magnetic sensors. This back bias magnet creates a predetermined magnetic field that interacts with the rotor's magnetic field to produce distinctive signal patterns, enabling more precise position detection while maintaining a relatively simple sensor structure
2Reliability
If position sensors are used to measure relative position in brushless DC motors, then accurate motor commutation is achieved, but the device complexity increases compared to brush-based systems
Solution Approach 1:
The magnetic sensor system serves multiple functions: it provides both radial and tangential magnetic field component detection, enables precise rotor position measurement, and works across different motor types (BLDC and reluctance motors). This multi-functionality achieves reliable commutation while minimizing the need for additional separate systems
Solution Approach 2:
The system uses the motor's own magnetic field (generated by rotor magnets) as the measurement source, eliminating the need for external measurement equipment. The back bias magnet and magnetic sensors work together to extract position information directly from the motor's operational magnetic field, achieving reliable commutation with minimal added complexity
3Measurement precision
If two magnetic sensors with different numbers of magnetic poles are used, then absolute rotation angle can be calculated with high precision, but the device complexity and manufacturing cost increase
Solution Approach 1:
Instead of using two complex encoders with different numbers of magnetic poles, the system changes the measurement parameters by using two magnetic sensors detecting different magnetic field components (radial and tangential). The back bias magnet transforms the single magnetic field into two measurable components, achieving high-resolution angle measurement through parameter differentiation rather than structural complexity
Solution Approach 2:
The system replaces the mechanical/structural approach of using multiple encoders with different pole counts with a magnetic field-based approach. By detecting different components of the magnetic field interacted with a back bias magnet, the system achieves the same measurement precision goal through electromagnetic field manipulation rather than mechanical encoder design
4Measurement precision
If the magnetic sensor system uses the Nonius or Vernier principle with multiple pole pairs, then the measurement precision of rotational displacement is improved, but the device complexity increases
Solution Approach 1:
The system achieves Vernier-like measurement precision by changing the measurement parameters - detecting both radial and tangential magnetic field components. The interaction between the back bias magnet's field and the rotor's magnetic field creates signal patterns that encode rotational position information with high precision, eliminating the need for complex physical encoder scales with multiple pole pairs
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 system enables precise determination of the rotor's position relative to the stator, allowing for accurate synchronization and commutation of the motor, improving performance and efficiency by providing reliable initial and subsequent shaft rotation angle information.
Implementation Method 1
detect changes in the magnetic field direction caused by the magnetic field interacting with two moveable targets that are being rotated by the motor shaft
Implementation Method 2
The magnetic sensors being configured to detect changes in the magnetic field direction
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
The present disclosure provides a magnetic sensor system for monitoring the position of the rotor relative to the stator for use in electronic motor commutation. The system uses two magnetic sensors with a back bias magnet, the magnetic sensors being configured to detect changes in the magnetic field direction caused by the magnetic field interacting with two moveable targets that are being rotated by the motor shaft. The unique phase shift between the signals measured at each sensor can thus be used to determine the relative position between the stator and the rotor. In this respect, the system makes use of the Nonius or Vernier principle to measure rotational displacement, however, the scale of the encoder is defined by the number of motor pole pairs.