Real-Time Orientation-Invariant Magnetic Localization and Sensor Calibration Based on Closed-Form Models

This paper presents a real-time orientation-invariant magnetic localization method based on a closed-form analytical inverse model. This method requires only a pair of inexpensive 3-axis magnetic sensors to acquire data for solving the unique solution of the inverse problem. Taking advantage of gravity, a permanent-magnet-upright device is designed to maintain a constant magnetic moment direction. An effective calibration method for the sensor orientation is proposed based on orthogonality to assure high performance. Then, a prototype magnetic localization system is developed. An in-depth experimental analysis is presented demonstrating the design feasibility of the tracking system in real time with a cycle-time less than 0.1 ms, and root-mean-square translation and rotation errors of 40 μm for a 40 mm × 40 mm × 50 mm volume and 0.16° for [-10°, 10°], respectively.