We propose a method to control the motion of a capsule endoscope (CE) in the stomach utilizing either a single external permanent magnet (EPM) or dual EPMs to extend the examination of the upper gastrointestinal tract. When utilizing the conventional magnetic navigational system (MNS) with a single EPM to generate tilting and rotational motions of the CE, undesired translational motion of the CE may prevent accurate examination. We analyzed the motion of the CE by calculating the magnetic torque and magnetic force applied to the CE using the point-dipole approximation model. Using the proposed model, we propose a method to determine the optimal position and orientation of the EPM to generate tilting and rotational motions without undesired translational motion of the CE. Furthermore, we optimized the weight of dual EPMs to develop a lightweight MNS. We prototyped the proposed MNS and experimentally verified that the developed MNS can generate tilting and rotational motions of the CE without any translational motion.

Helical magnetic robots driven by an external magnetic field have been extensively studied for robotic endovascular intervention to treat occlusive vascular disease. Most previous researchers have utilized cone-shaped head helical magnetic robots (CHMRs) with helical blades for thrombus drilling. However, the CHMR may become stuck in the thrombus or drilling performance may be significantly reduced after the cone-shape head enters the thrombus. We propose a sawtooth head helical magnetic robot (SHMR) to improve drilling performance. Furthermore, the pitch length of the SHMR was optimized experimentally. Finally, improved drilling performance of the SHMR compared to CHMR was verified by in vitro drilling experiments with a pseudo thrombus containing 0.8 wt. %, 1.0 wt. %, and 1.2 wt. % agar.

Magnetic helical robots (MHRs) can be actuated by a rotating magnetic field (RMF) and can tunnel through a clogged blood vessel using their rotational motion. We propose a method minimizing the voltage required for each coil to generate the RMF for a magnetic navigation system (MNS). The proposed method maximizes the RMF under the rated voltage of the MNS. In addition, to suppress the increase in impedance during high-speed rotational motion of the MHR, the proposed method utilizes the resonance to which the minimax optimization method is applied. The voltage needed to generate the RMF was analytically derived, with the goal of a fast optimization process in mind, so that the MHR could be controlled in real-time. The proposed method was experimentally verified by measuring the magnetic flux density. In addition, we demonstrated the enhanced navigating and tunneling performance of the MHR from in vitro experiments. Finally, we validated the navigating and tunneling motion of the MHR in an in vivo experiment within a superficial femoral artery of a pig.

In this paper, we propose a method of identifying the position of a tethered delivery catheter in a vascular environment, recombining an untethered magnetic robot (UMR) to the tethered delivery catheter, and safely retrieving them from the vascular environment in an endovascular intervention by utilizing a separable and recombinable magnetic robot (SRMR) and a magnetic navigation system (MNS). From images of a blood vessel and a tethered delivery catheter taken from two different angles, we developed a method of extracting the position of the delivery catheter in the blood vessel by introducing dimensionless cross-sectional coordinates. Then, we propose a retrieval method for the UMR by using the magnetic force considering the delivery catheter’s position, suction force, and rotating magnetic field. We used thane MNS and feeding robot to simultaneously apply magnetic force and suction force to the UMR. In this process, we determined a current solution for generating magnetic force by using a linear optimization method. Finally, we conducted in vitro and in vivo experiments to verify the proposed method. In the in vitro experiment, which was in a glass tube environment, by using an RGB camera, we confirmed that the location of the delivery catheter in the glass tube could be recognized within an average error of 0.05 mm in each of the X- and Z-coordinates and that the retrieval success rate was greatly improved in comparison with that in the case without the use of magnetic force. In an in vivo experiment, we successfully retrieved the UMR in the femoral arteries of pigs.

Magnetic helical robots (MHRs) actuated by an external magnetic field have been regarded as a possible application to treat occlusive vascular disease. We propose a pecking motion of an MHR to effectively tunnel an occlusive vascular lesion. The pecking motion is composed of a rotational driving motion and a linear impulsive motion of the MHR actuated by alternating rotating magnetic field (ARMF). The minimum magnetic flux density to synchronize the MHR to ARMF was mathematically determined from the equation of motion of the MHR and was experimentally verified. Finally, enhanced tunneling performance of the MHR with the pecking motion was verified by in vitro tunneling experiments with a pseudo-thrombus.

We propose an optimization algorithm to generate a robust magnetic force against position error to achieve good controllability of the magnetic robot in the region of interest of a magnetic navigation system comprising electromagnets. We formulate an optimization problem that minimizes the norm of the spatial derivatives of the magnetic force subject to the constraints of the magnetic flux density and magnetic force. The robust magnetic force generated by the proposed algorithm was compared with conventional pseudo-inverse matrix method and verified through an experiment in which a magnetic robot was successfully steered along a bifurcated glass tube to reach a target position.