Pose-Independent Interaction Distance Adjustment for Magnetically Driven Robotic Capsules

Safe capsule-colon interaction for magnetically driven robotic capsules is important in clinical applications. This work presents a solution based on the amplitude information of the magnetic field to adjust the distance between the interacting magnets, in order to prevent the magnetic forces exerted on the capsule robot and the pressure on the intestine walls from being overlarge, which may cause large deformation of the colon. As the first step, the geometry of the internal magnet embedded in the capsule is optimized to approach a near-spherical amplitude of the magnetic field based on the dipole model. Next, mathematical mapping from magnetic field amplitude to the interaction distance between the magnets is presented with constraint derivation and implementation. Then, a strategy to adjust the distance between the interacting magnets is provided based on the mapping using the magnetic field information. Finally, experiments are designed to validate the pose-independent interaction distance adjustment. Compared with the previous work, the proposed solution enables the quick interaction distance adjustment between the magnets to enhance the safety of capsule-colon interaction in the magnetically driven capsule endoscopies, since the interaction distance is derived straightforwardly from the magnetic field signals, without requiring the prerequisite implementation of capsule localization.