Magnet Ring Pole Boundary Sensing for Runout Error Correction
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Solution Overview
Problem
Rotary joint devices, such as brushless DC motors, face accuracy issues due to environmental changes and mechanical runout, which affect the determination of angular position and encoder error, particularly in robotic and automotive systems.
Innovation Solution
A processing system generates a magnetic field that interacts with a magnet ring's poles, using magnetic field sensors to detect shifts and determine the angular position, then removes sinusoidal runout errors to improve accuracy and correct for mechanical and encoder errors.
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 environmental changes affecting the fingerprint readout
Solution Approach 1:
The system performs preliminary characterization of the magnetic field pattern and runout effects during a calibration phase before actual operation. By pre-determining the relationship between sensor signals and angular position including runout characteristics, the system establishes a reference model that compensates for environmental variations during subsequent measurements
Solution Approach 2:
The system uses the magnetic field sensor signals as feedback to continuously monitor and adjust the angular position determination. By comparing actual sensor readings against the calibrated model and iteratively refining the position calculation, the system compensates for environmental changes and maintains accuracy
2Measurement precision
If magnetic field sensors are used to detect pole boundaries and determine angular position, then measurement capability is improved, but measurement precision deteriorates due to runout error
Solution Approach 1:
The system extracts and separates the runout component from the magnetic field sensor signal by analyzing the periodic variations caused by mechanical runout. By identifying and isolating this specific error component, the system can remove it from the position calculation, leaving only the true angular position information
Solution Approach 2:
The system creates a digital model or copy of the runout error pattern by measuring it during calibration or operation. This virtual replica of the runout characteristics is then used to correct actual measurements by applying the inverse of the identified error pattern, effectively canceling out the runout effect
3Reliability
If the system accounts for runout and dynamic loading changes to improve accuracy, then reliability is improved, but device complexity increases
Solution Approach 1:
The system uses its own operational data and sensor signals to automatically characterize and compensate for runout effects without requiring external calibration equipment or complex additional hardware. By leveraging the existing magnetic field sensor readings and motor operation information, the system performs self-calibration and self-correction
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 method enhances the accuracy of angular position determination and motor calibration by accounting for runout and dynamic loading changes, improving the reliability of rotary joint devices.
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.