Jaekwang Nam

Reduction of Magnetically Induced Vibration of a Spoke-Type IPM Motor Using Magnetomechanical Coupled Analysis and Optimization

We present an optimization methodology to reduce magnetically induced vibrations of a spoke-type interior permanent magnet (IPM) motor that we developed by performing magnetic and structural finite element analyses and optimization. The magnetic forces acting on the teeth of the stator were calculated by magnetic finite element analysis and the Maxwell stress tensor method. The natural frequencies and mode shapes of the stator were calculated by structural finite element analysis and verified by modal testing. The vibration of the motor due to the rotating magnetic force was calculated by the mode superposition method, and it was compared with the measured vibration. Finally, two optimization problems were formulated and solved to reduce magnetically induced vibration: minimization of magnetic force and minimization of acceleration. We showed that minimization of acceleration was more effective than minimization of magnetic force at reducing magnetically induced vibrations, because the former method effectively decreased the amplitudes of the excitation frequencies of magnetic force by considering the transfer function of the motor.

A self-positioning and rolling magnetic microrobot on arbitrary thin surfaces

We propose a novel self-positioning and rolling magnetic microrobot (SPRMM) actuated by a magnetic navigation system. The proposed microrobot can effectively anchor or move on an arbitrary three-dimensional thin surface by overcoming external forces. Furthermore, we derive a no-slip rolling constraint equation for the SPRMM. We also examine the equilibrium characteristics of the SPRMM by utilizing the point-dipole model. Experiments demonstrating the locomotion abilities of the SPRMM in complex working environments are then conducted to verify the proposed SPRMM.

Magnetically Induced Vibrations in an IPM Motor Due to Distorted Magnetic Forces Arising From Flux Weakening Control

This research investigates the characteristics of magnetic forces and magnetically induced vibrations due to changes in the phase angle of applied current arising from flux weakening control of an interior permanent magnet (IPM) motor. The magnetic force is analyzed using the Maxwell stress tensor method, and the vibration induced by the application of a rotating magnetic force is analyzed using the mode superposition method. The experiments are conducted to validate the simulated vibrations due to the distorted magnetic forces. This research shows that flux weakening control may increase the magnetically induced vibration due to increases in tangential magnetic forces.

Capsule-Type Magnetic Microrobot Actuated by an External Magnetic Field for Selective Drug Delivery in Human Blood Vessels

In this paper, we propose a novel capsule-type magnetic microrobot (CMM) that can navigate along a tubular environment and selectively release drugs in different target points actuated by a magnetic navigation system. The proposed CMM is a capsule-type structure with two cylindrical drug chambers that contain different drugs. It can navigate through a tubular environment by a magnetic gradient and release drugs at different positions by using uniform rotating magnetic fields. The proposed CMM was prototyped using 3-D printing technology. The operating conditions of a drug-releasing motion were determined by investigating the magnetic and friction torques within the body. Finally, we performed various experiments in a tubular environment to verify the validity of the proposed CMM.

Dual-body magnetic helical robot for drilling and cargo delivery in human blood vessels

We propose a novel dual-body magnetic helical robot (DMHR) manipulated by a magnetic navigation system. The proposed DMHR can generate helical motions to navigate in human blood vessels and to drill blood clots by an external rotating magnetic field. It can also generate release motions which are relative rotational motions between dual-bodies to release the carrying cargos to a target region by controlling the magnitude of an external magnetic field. Constraint equations were derived to selectively manipulate helical and release motions by controlling external magnetic fields. The DMHR was prototyped and various experiments were conducted to demonstrate its motions and verify its manipulation methods.

Control of a three-dimensional magnetic force generated from a magnetic navigation system to precisely manipulate the locomotion of a magnetic microrobot

We propose a method to generate a three-dimensional (3D) magnetic force to manipulate a magnetic microrobot in various environments by using a magnetic navigation system. The proposed method is based on the control of the magnetic force with respect to the change in the magnetization direction of the microrobot and an external magnetic flux gradient. We derived the nonlinear constraint equations which can determine the required direction of the uniform magnetic fields and magnetic gradients to generate the 3D magnetic force of a microrobot. The solutions of the equations were calculated using a geometrical analysis of the equations without any singular point. The proposed methodology was verified on 3D planar environments considering gravitational force, and we also conducted an experiment in a 3D water-filled tubular environment to verify the possibility of the clinical application in human blood vessels.

A crawling and drilling microrobot driven by an external oscillating or precessional magnetic field in tubular environments

We propose a crawling and drilling microrobot actuated by an external precessional magnetic field (EPMF) to effectively unclog obstructed blood vessels. Conventional crawling microrobots can only generate crawling motions using an external oscillating magnetic field. The proposed microrobot can generate navigating (crawling) and drilling motions selectively or simultaneously by controlling the EPMFs. We prototyped the proposed microrobot, and conducted several experiments to verify the efficacy of the crawling and drilling ability of the microrobot in a tubular environment.

Selective Motion Control of a Crawling Magnetic Robot System for Wireless Self-Expandable Stent Delivery in Narrowed Tubular Environments

A novel crawling magnetic robot system manipulated by a magnetic navigation system is proposed for wireless self-expandable stent delivery in narrowed tubular environments. The crawling magnetic robot is composed of a crawling module to generate crawling motion for navigation in a tubular environment, and a magnetic pulley module to generate drilling motion to unclog the blocked region and uncovering motion of a stent cover for the self-expandable stent deployment. The magnetic navigation system composed of three orthogonal pairs of electromagnetic coils can generate three dimensional external magnetic field by controlling the applied current. We also proposed selective motion control methods and design processes with fabrication. Finally, we prototyped the proposed crawling magnetic robot and conducted several experiments to show the validity of the proposed crawling magnetic robot and its manipulation methods.

Effective Locomotion and Precise Unclogging Motion of an Untethered Flexible-Legged Magnetic Robot for Vascular Diseases

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 magnetic minirobot with anchoring and drilling ability in tubular environments actuated by external magnetic fields

We propose a magnetic minirobot with anchoring and drilling ability (MMAD) controlled by an external magnetic field. The proposed MMAD can navigate through a tubular environment, such as human blood vessels, actuated by a magnetic gradient and uniform rotating magnetic field. It can also generate an anchoring motion, which stably holds the position of the MMAD under pulsatile flow, in order to drill and unclog obstructed blood vessels. The operating conditions of the MMAD were examined by investigating the magnetic torques, and the holding force of the MMAD was measured by a force sensing resistor. Finally, we performed various experiments in a tubular environment to verify the validity of the proposed MMAD.