E-compass tilt calibration via ellipse-fitting procedure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing navigation systems using e-compass and accelerometers suffer from inaccuracies due to tilt errors and magnetic disturbances, leading to unreliable direction signals, especially in portable devices like cell phones where power efficiency and accuracy are critical.
Innovation Solution
An electronic circuit and process that includes an e-compass with sensors on different axes, memory circuitry, and a processor executing an ellipse-fitting procedure to generate tilt calibration parameters, allowing for accurate correction of heading measurements by compensating for residual tilt errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If accelerometer-based tilt estimation is used for e-compass correction, then power consumption is reduced and device complexity is lowered, but measurement precision deteriorates due to residual tilt errors
Solution Approach 1:
The system performs preliminary calibration by executing an ellipse-fitting procedure during device initialization or setup phase. This pre-calibration establishes correction parameters (ellipse center, axes lengths, orientation) that are stored for subsequent use, eliminating the need for complex real-time tilt compensation algorithms during normal operation.
Solution Approach 2:
The patent introduces an intermediate calibration model (ellipse parameters) that mediates between raw e-compass measurements and corrected heading values. Instead of directly compensating for tilt using accelerometer data, the system uses the ellipse-fitting model as an intermediary to transform and correct the magnetic field measurements, simplifying the overall correction process.
2Measurement precision
If complex tilt compensation algorithms are implemented, then measurement precision improves, but use of energy increases and productivity decreases
Solution Approach 1:
Complex computational tasks (ellipse-fitting procedure) are performed in advance during calibration phase rather than in real-time during heading calculations. The pre-computed ellipse parameters are stored and applied through simple transformations during normal operation, significantly improving calculation speed while maintaining accuracy.
Solution Approach 2:
The system performs a complete ellipse-fitting procedure that may be more comprehensive than strictly necessary, fitting an ellipse to all calibration data points rather than using simplified approximation methods. This excessive action ensures maximum measurement precision while the pre-computation approach maintains high productivity during actual use.
3Reliability
If accelerometer data is used for tilt estimation, then device complexity is reduced, but reliability deteriorates due to inherent accelerometer errors
Solution Approach 1:
The patent uses the ellipse-fitting model as an intermediary that processes raw e-compass measurements independently of accelerometer reliability. The calibration procedure fits an ellipse to magnetic field measurements taken during device rotation, creating a transformation model that corrects heading errors without directly relying on potentially inaccurate accelerometer tilt estimates.
Solution Approach 2:
The e-compass system performs self-calibration by utilizing its own measurement capabilities during a calibration routine. The device collects magnetic field data at multiple orientations, fits an ellipse to this self-generated data, and derives correction parameters autonomously, eliminating dependence on external accelerometer data for the core correction mechanism.
Data Source
AI summary
An electronic circuit includes an electronic compass having e-compass sensors mounted on different axes and operable to supply e-compass sensor data, memory circuitry, and an electronic processor coupled to said e-compass sensors and to said memory circuitry, said electronic processor operable to execute an electronic ellipse-fitting procedure responsive to the e-compass sensor data to generate at least one signal related to an ellipse tilt angle, and store the at least one signal in said memory circuitry as a tilt calibration parameter for the e-compass. Processes for calibrating an e-compass, as well as electronic circuits and processes for correcting measured heading, and processes of manufacture are also disclosed.