Off-axis Turn Counter for Rotational Angle Sensing
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Solution Overview
Problem
Existing solutions for sensing the rotational angle of a shaft from an off-axis position are inefficient and lack accuracy, especially at high rotation speeds and varying diameters, due to limitations in detecting magnetic field components and counting magnetic poles.
Innovation Solution
An off-axis counter system that uses a combination of magnetic sensing elements and a turn counter to detect and count magnetic poles modulo an integer number, allowing for accurate angle measurement by combining signals from sensing elements and the counter, which can be integrated with a multipole magnet and circuitry for efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If magnetic sensing elements are used to detect magnetic field components from an off-axis position, then angle measurement can be performed without direct shaft access, but measurement precision deteriorates especially at high rotation speeds
Solution Approach 1:
The magnetic field detection is segmented into multiple orthogonal components (e.g., radial and tangential components detected by separate sensing elements). By dividing the measurement into discrete components that can be processed independently and combined through modulo arithmetic, the system achieves both off-axis operation and high precision angle measurement even at high rotation speeds.
2Reliability
If a turn counter is used to count magnetic poles, then rotational position can be tracked, but reliability deteriorates due to pulse missing at high rotation speeds
Solution Approach 1:
The patent introduces magnetic pole pairs as an intermediary structure between the rotating shaft and the off-axis sensor. By using a multipole magnet configuration where multiple poles are distributed around the shaft circumference, the system creates multiple detection points that allow the turn counter to track rotations reliably even at high speeds, preventing pulse loss through redundant detection opportunities.
3Measurement precision
If sensing elements are arranged around the reading circle, then angle measurement coverage is improved, but device complexity increases
Solution Approach 1:
The patent designs the magnetic sensing elements to perform multiple functions: they detect both radial and tangential magnetic field components, enable angle measurement through orthogonal component analysis, and support turn counting for rotational position tracking. This multi-functionality reduces the need for separate sensor systems, thereby lowering overall device complexity while maintaining high measurement precision.
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 provides a cost-effective and stable method for determining the angular position of a shaft with high accuracy at high rotation speeds and flexibility in scaling the magnetic field for different diameters, without missing pulses even without electrical power, and reduces errors by using a multipole magnet with a ring or donut shape.
Implementation Method 1
a magnetic sensing element that is arranged to detect the magnetic field of the magnetic field source
Implementation Method 2
the chip or an effective surface of the chip is arranged perpendicular to a radial direction (r-direction). This guarantees a magnetic field component parallel to the chip surface, which rotates 360° when one pole-pair passes the chip
Data Source
AI summary
An off-axis counter is suggested that is arranged to count magnetic poles of a magnetic field source that turns around a rotation axis modulo an integer number. Also, a rotation angle sensing device and a method for determining a rotation angle are provided.