Managing the attractive magnetic force between an untethered magnetically actuated tool and a rotating permanent magnet

Untethered magnetic devices, such as magnetic microrobots and magnetically actuated capsule endoscopes, stand to significantly impact the field of minimally invasive medicine. These devices, which we refer to as magnetically actuated tools (MATs), are often controlled using electromagnets, which can be expensive to scale clinically. Due to their potential for low-cost and high strength, permanent magnets are being considered for MAT actuation. Great care must be taken for in vivo medical applications, however, as systems using single permanent magnets typically generate an attractive force, which may cause trauma if uncontrolled. In this paper, we present techniques for managing the attractive magnetic force. We find that in the case of rotating MATs actuated using a single rotating permanent magnet (RPM), for which magnetic torque is the primary form of actuation, the attractive magnetic force can be substantially reduced in magnitude and the time-averaged attractive component eliminated when operating the MAT such that magnetic torque is maximized. We provide experimental demonstration that validates and illustrates the force management strategies presented.