Magnet Ring Runout Compensation for Angular Position Sensing
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Solution Overview
Problem
Rotary joint devices, such as brushless DC motors, experience inaccuracies in determining angular position due to environmental changes and runout errors, which affect the accuracy of encoder readings.
Innovation Solution
A method is described to generate and measure magnetic fields from a magnet ring with jittered poles, using magnetic field sensors to determine the angular position and correct for runout by calculating the phase shift and removing sinusoidal components from the signal to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnet ring with jittered poles is used to provide a unique fingerprint for determining angular position, then the ability to determine angular position is improved, but accuracy deteriorates due to runout errors and environmental changes affecting the fingerprint readout
Solution Approach 1:
The system performs preliminary characterization of runout errors by analyzing magnetic field signal variations during rotation. The runout profile is determined in advance through signal processing (Fourier transform analysis) and stored as compensation data. This preliminary action allows the system to pre-calculate correction factors that are then applied during normal operation to compensate for runout effects on the angular position measurement accuracy.
2Adaptability or versatility
If environmental conditions change, then operational flexibility is improved, but accuracy of encoder readings deteriorates due to effects on the unique fingerprint readout
Solution Approach 1:
The system continuously monitors the magnetic field signal characteristics during rotation and compares actual readings against the stored runout compensation profile. Based on this feedback, the system dynamically adjusts the angular position calculation by applying real-time corrections. This feedback mechanism enables the system to maintain accurate measurements despite environmental changes such as temperature variations or mechanical loading that may affect the encoder readings.
3Measurement precision
If runout compensation is implemented through signal processing, then measurement accuracy is improved, but device complexity increases due to additional processing requirements
Solution Approach 1:
The system replaces complex mechanical runout compensation mechanisms (such as precision mechanical alignment systems or physical runout correction devices) with electronic signal processing. By using Fourier transform analysis and digital signal processing techniques on the magnetic field encoder signals, the system achieves runout compensation through computational methods rather than mechanical means, thereby reducing overall device complexity while maintaining or improving measurement accuracy.
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 enhances the accuracy of angular position determination in rotary joint devices by compensating for runout and encoder errors, leading to improved calibration and operational reliability.
Implementation Method 1
generating a first magnetic field that interacts with a second magnetic field generated by four or more poles of a magnet ring mounted to a first platform. The magnetic field may cause the first platform to rotate about an axis of rotation relative to a second platform
Implementation Method 2
receiving, from a magnetic field sensor connected to the second platform, data indicative of characteristics of the second magnetic field
Data Source
AI summary
A method for determining runout error includes generating a first magnetic field to interact with a second magnetic field generated by four or more poles of a magnet ring mounted to a first platform. The interaction may cause the first platform to rotate relative to a second platform. The method may further include receiving, from a magnetic field sensor, data including respective boundaries between neighboring poles of the four or more poles relative to a corresponding nominal boundary defined by substantially uniform boundary spacing. The method may include determining a magnetic field pattern from the data and, based on the pattern, determining an angular position of the four or more poles. The method may further include determining an angular difference between the determined angular position and a nominal angular position. The method may also include determining a runout error based on an amplitude of the angular difference.