Patent attributes
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.
