We propose a novel closed-circuit magnetic navigation system (CMNS), which utilizes eight electromagnets connected by back yokes to maximize a magnetic field. We first show the effectiveness of a closed magnetic circuit (CMC) and conduct a parametric analysis to design a single CMC, which is utilized to construct the whole CMNS. A magnetic field mapping method is also developed utilizing the finite-element method and polynomial regression to evaluate and control the magnetic field over almost the whole workspace in real time. We investigated how the magnetic field changed based on the shape of core tips by comparing the isotropic magnetic field control authority, which is the ability to generate an equal magnetic field over the workspace regardless of the position and direction of the magnetic field. We experimentally verified the mathematical assumption that the magnetic field generated from the proposed CMNS can be linearly proportional to the applied current and that the magnetic field of the proposed CMNS can be expressed as a superposition of the magnetic fields generated by each electromagnet. Finally, we verified the effectiveness of the developed CMNS by performing experiments related to steering a commercial magnetic catheter.

We propose an untethered flexible-legged magnetic robot (FLMR) manipulated by an external rotating magnetic field (ERMF) to generate effective locomotion and precise unclogging motion to treat vascular diseases. The proposed FLMR is composed of a front body with a drill tip, a cylindrical permanent magnet, a rear body, and flexible legs. The flexible legs are obliquely attached to the bodies like blades of a propeller, so that the FLMR can generate propulsive force in a fluidic environment for locomotion and unclogging motions. To provide manipulation guidelines for locomotion and unclogging motions, we developed a dynamic model of propulsive force, axial force, and friction force, and we established a control method of propulsive force according to the rotating frequency of the ERMF and the diameter of the tube, based on the proposed dynamic model. Finally, we prototyped the FLMR and conducted several experiments to verify its navigation performances and the control method of the propulsive force. Also, we conducted an in vitro experiment with a pseudo blood clot to demonstrate the validity of the locomotion and unclogging motions of the FLMR.

A multifunctional magnetic catheter robot (MCR) is proposed in this paper to treat occlusive vascular disease by generating steering, tunneling, and stent delivery motions. Using external magnetic fields generated by a closed-loop magnetic navigation system, the MCR can be manipulated remotely and can generate each motion by magnetic manipulation methods. The MCR has novel structures with a magnetic joint and tension springs for selective stent delivery. Constraints and a dynamic model were derived to specify the manipulation conditions for the selective treatment motions and design parameters of the MCR. Then, the MCR was prototyped, and the steering, tunneling, and stent delivery motions were verified by several experiments. Finally, an in vitro experiment with a pseudo blood clot was conducted to demonstrate the effectiveness of the MCR and its motions for the treatment of occlusive vascular disease.

This paper proposes a method to calculate the characteristics of a coupled fluid dynamic journal and thrust bearing of a hard disk drive (HDD) spindle motor. The governing equations for the journal and thrust bearings are the two-dimensional Reynolds equations in the $θz$ and $rθ$ planes, respectively. The finite element method is appropriately applied to analyze the coupled bearing under the conditions of the continuity of mass and pressure at the interface between the journal and thrust bearings. The pressure in the coupled bearing was calculated by applying the Reynolds boundary condition. The validity of this application was verified by comparing the analytical results of the flying height at various rotating speeds with experimental results. The characteristics of the coupled journal and thrust bearing were also investigated due to the Reynolds and Half-Sommerfeld boundary conditions and the coupled and separate analysis. This research demonstrates that the proposed method can accurately and realistically describe the coupled fluid dynamic bearing in a HDD system.

We developed a magnetic navigation system (MNS) composed of a magnetic field control part and a robot arm part to precisely control the position and posture of a capsule endoscope (CE). The magnetic field control part generates a magnetic field by controlling the magnetization directions of dual permanent magnets (PMs) using motors, and the robot arm part supports and freely moves the magnetic field control part in three dimensions. First, we calculated the magnetic field generated by the dual PMs of the MNS by utilizing point-dipole approximation, and the magnetic force between the PMs of the MNS and the CE. We set up an optimal design problem to determine the rotational angles of the magnetization direction of the dual PMs of the MNS to align the CE to the given direction. We validated the proposed optimal design problem by utilizing finite element analysis. By using the developed MNS and a commercial CE, we measured the magnetic force acting on the CE and compared it with the simulated results of the finite element analysis. Finally, we performed a gastric endoscopy in a mimetic stomach and confirmed that the proposed MNS can effectively examine the major parts of a stomach.