3D Path-Following Using MRAC on a Millimeter-Scale Spiral-Type Magnetic Robot

This letter focuses on the 3D path-following ofa spiraltype helical magnetic swimmer in a water-filled workspace. The swimmer has a diameter of 2.5 mm, a length of 6 mm, and is controlled by an external time-varying magnetic field. A method to compensate undesired magnetic gradient forces is proposed and tested. Five swimmer designs with different thread pitch values were experimentally analyzed. All were controlled by the same model reference adaptive controller (MRAC). Compared to a conventional hand-tuned PI controller, their 3D path-following performance is significantly improved by using MRAC. At an average speed of 50 mm/s, the path-following mean error of the MRAC is 3.8 ± 1.8 mm, less than one body length of the swimmer. The versatility of this new controller is demonstrated by analyzing pathfollowing through obstacles on a helical trajectory and forward & backward motion.