Magnetometer Calibration for Cart Navigation Using 3-Axis Coils
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Solution Overview
Problem
Existing navigation systems for human-propelled wheeled carts face challenges in accurately calibrating magnetometers due to soft iron distortions caused by ferromagnetic materials in the cart handles, which affect the accuracy of position determination using dead reckoning techniques.
Innovation Solution
A method involving pre-installation and post-installation calibration of magnetometers using a 3-axis magnetic coil system to generate controlled magnetic fields, allowing for the creation of calibration models that account for soft iron distortions, and storing these models in non-transitory memory for correction during navigation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetometer calibration is performed without accounting for soft iron distortions, then calibration process is simple, but measurement precision deteriorates due to ferromagnetic interference from cart handles
Solution Approach 1:
A 3-axis magnetic coil system is introduced as an intermediary device to generate controlled magnetic fields during calibration. The coil system acts as a mediator between the calibration process and the magnetometer, enabling precise field application while isolating the magnetometer from uncontrolled ferromagnetic interference. This intermediary system allows for systematic calibration that accounts for soft iron distortions without requiring complex manual procedures.
Solution Approach 2:
The calibration process is performed in advance (pre-installation) and after installation (post-installation) to establish baseline characteristics and correction factors before the magnetometer is subjected to operational conditions. By performing preliminary calibration actions, the system captures the magnetometer's response to controlled fields and later uses this data to compensate for soft iron distortions during actual navigation, improving measurement precision without adding complexity to real-time operation.
2Measurement precision
If pre-installation and post-installation calibration both are performed, then measurement precision improves, but loss of time increases due to extended calibration process
Solution Approach 1:
Pre-installation calibration is performed in advance during manufacturing or setup, establishing the magnetometer's baseline characteristics and generating initial calibration models. This preliminary action captures the sensor's response to controlled magnetic fields before installation, allowing post-installation calibration to focus only on compensating for specific cart handle interference rather than performing complete calibration again, thereby reducing total calibration time while maintaining high navigation accuracy.
Solution Approach 2:
The calibration process针对不同 stages (pre-installation and post-installation) applies different calibration models and field configurations tailored to specific needs. Pre-installation calibration uses a first calibration model for baseline characterization, while post-installation calibration uses a second model focused on soft iron distortion compensation. This localized approach to calibration quality ensures comprehensive accuracy without redundantly repeating all calibration steps, optimizing the time-precision tradeoff.
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 significantly improves the accuracy of magnetometer readings by compensating for soft iron distortions, enhancing the precision of dead reckoning navigation systems by generating highly accurate nonlinear models of magnetometer responses.
Implementation Method 1
a magnetic coil system configured to generate a magnetic field in response to an applied current
Data Source
AI summary
A wheeled object (e.g., a human-propelled cart such as a shopping cart) can include a navigation system that uses dead reckoning to determine the position of the wheeled object. The navigation system can include a magnetometer and an accelerometer and may be disposed on a handle of the wheeled object. Examples of a system for calibrating the magnetometer and accelerometer during manufacture as well as during installation on the wheeled object are disclosed. The calibration includes calibrating for the soft iron distortion induced at the navigation system by the ferromagnetic shopping cart handle (or other ferromagnetic portions of the cart such as the frame) and hard iron distortions induced by nearby magnetic sources (e.g., a permanent magnet in an audio speaker). The calibration system can include a plurality of Helmholtz or Maxwell coils.