Noncontacting Position and Orientation Estimation of a Centimeter-Scale Robot Using an Active Electromagnet

This article focuses on estimating the position and orientation of a three degree-of-freedom (DoF) robot using a novel electromagnet-based active control system. The electromagnet is mounted on a servo motor and its orientation is controlled in real time so that it always points at the robot. A two-axis magnetic sensor on the robot helps determine both its radial distance from the electromagnet and its orientation. The active pointing control of the electromagnet highly simplifies the position estimation problem. Instead of requiring a magnetic field model that is a function of all three DoF, the radial distance and robot orientation estimation tasks become decoupled and independent problems. The radial distance is estimated using an asymptotically stable nonlinear observer designed using a linear matrix inequality. The analytical principles of the estimation system are first presented using key technical lemmas and proofs. Extensive experimental results are then presented on the performance of the estimation system, including real-time estimation of the moving robot's position and orientation.