G. H. Jang

Two-dimensional actuation of a microrobot with a stationary two-pair coil?system

This paper proposes a new two-dimensional (2D) actuation method for a microrobot that uses a stationary two-pair coil system. The coil system actuates the microrobot by controlling the magnitude and direction of the external magnetic flux. The actuation of the microrobot consists of an alignment to the desired direction and a linear movement of the microrobot by non-contact electromagnetic actuation. Firstly, the actuation mechanism of the stationary coil system is theoretically derived and analyzed. Secondly, the tendency of the magnetic flux in the coil system are analyzed and compared by preliminary theoretical analysis. Through various locomotive experiments of the microrobot, the performance of the electromagnetic actuation by the proposed stationary two-pair coil system is evaluated. Using the proposed 2D actuation method, the microrobot is aligned to the desired direction by Helmholtz coils and is driven to the aligned direction by Maxwell coils. By the successive current control of the coil system, the microrobot can move along a desired path, such as a rectangular-shaped or a diamond-shaped path.

Magnetic navigation system for the precise helical and translational motions of a microrobot in human blood vessels

Different magnetic navigation systems (MNSs) have been investigated for the wireless manipulation of microrobots in human blood vessels. Here we propose a MNS and methodology for generation of both the precise helical and translational motions of a microrobot to improve its maneuverability in complex human blood vessel. We then present experiments demonstrating the helical and translational motions of a spiral-type microrobot to verify the proposed MNS.

Cogging Torque of Brushless DC Motors Due to the Interaction Between the Uneven Magnetization of a Permanent Magnet and Teeth Curvature

This research investigates the characteristics of cogging torque in brushless DC motors due to the interaction between the uneven magnetization of a permanent magnet and the shape of the teeth. The excitation frequencies of the cogging torque are the harmonics of the least common multiple of the poles and slots in ideal brushless DC motors. However, this research numerically and experimentally illustrates that the uneven magnetization of a permanent magnet also generates the harmonics of slot number. Magnitudes of cogging torque are affected not only by the uneven magnetization of a permanent magnet but also by the shape of the teeth. The cogging torque can be effectively reduced by determining optimal teeth curvature once the range of uneven magnetization of permanent magnet in a brushless DC motor is identified.

Characterization and Experimental Verification of the Axial Unbalanced Magnetic Force in Brushless DC Motors

The characteristics of the axial unbalanced magnetic force (UMF) in brushless dc (BLDC) motors were numerically and experimentally investigated. Three-dimensional finite element analysis was conducted to characterize the axial UMF. An experimental device was also developed to measure the axial UMF and verify the simulated results. The axial asymmetry of the permanent magnet (PM) with respect to the stator was found to be a major source of the axial UMF, whose driving frequencies are the least common multiples of the pole and slot. Additional uneven magnetization of the PM and rotor eccentricity introduce slot harmonics to the axial UMF, while additional stator eccentricity generates fundamental and pole harmonics.

Axial Shock-Induced Motion of the Air-Oil Interface of Fluid Dynamic Bearings of a Non-Operating Hard Disk Drive

We investigated the axial shock-induced motion of the air-oil interface of the fluid dynamic bearings (FDBs) of a non-operating (HDD) by experiment and simulation. We empirically determined the motion of the rotor with respect to the stator and the oil leakage due to axial shock. We applied the finite volume method and the volume of fluid method to simulate the axial shock-induced motion of the fluid lubricant of FDBs considering the two-phase flow of air and oil and the surface tension at the air-oil interface. The thrust plate and shaft were assumed to move as a rigid body. Our findings allow us to explain the phenomenon of the break-up of the air-oil interface of FBDs caused by axial shock. We also discuss the effects of the magnitude of the shock and oil viscosity on the break-up of the air-oil interface.

Precise manipulation of a microrobot in the pulsatile flow of human blood vessels using magnetic navigation system

This paper proposes a method to precisely manipulate a microrobot in the pulsatile flow that simulates the flow characteristics of human blood vessels by utilizing the electromagnetic transfer function of a magnetic navigation system (MNS). The frequency response characteristics of the MNS were utilized so that the input voltages in each coil can precisely generate the required time-varying magnetic force of a microrobot. An experiment which successfully anchoring a microrobot in a pulsatile flow was conducted to verify the proposed method.

Utilization of Magnetic Gradients in a Magnetic Navigation System for the Translational Motion of a Micro-Robot in Human Blood Vessels

This paper proposes a method to generate the translational motions of a micro-robot in human blood vessels by utilizing the magnetic gradients of a magnetic navigation system (MNS). The proposed method was applied to the MNS composed of a Maxwell coil, Helmholtz coil, and uniform and gradient saddle coils, and it was verified through the experiment demonstrating the rectilinear and translational motions of a micro-robot in a plane. This paper also discusses the effective aligning angle for the translational motion of a micro-robot to reduce the required magnetic gradients of the MNS. This research contributes to the effective and therapeutic manipulation of a micro-robot in human blood vessels.

Development of a New Magnetizing Fixture for the Permanent Magnet Brushless DC Motors to Reduce the Cogging Torque

Excitation frequencies of cogging torque in a brushless dc motor are composed of the fundamental and its harmonics of the least common multiple of the poles and slots in ideal brushless dc motors, and the slot harmonics of the multiple of slot number due to the manufacturing errors. One of the main sources of the slot harmonics is the uneven magnetization of the permanent magnet. We investigated numerically and experimentally the uneven magnetization of permanent magnet due to the design of the magnetizing fixture and its effect on the harmonics of cogging torque. We proposed a new design of the magnetizing fixture to uniformly magnetize the permanent magnet in such a way to reduce both the fundamental harmonic and the slot harmonics of cogging torque. The slot harmonics and the fundamental harmonic of cogging torque of a brushless dc motor can be suppressed by including the back-yoke and the slots of the teeth in the magnetizing fixture, respectively.

Precise Steering and Unclogging Motions of a Catheter With a Rotary Magnetic Drill Tip Actuated by a Magnetic Navigation System

We developed a novel structure of a catheter actuated by an external magnetic field. The catheter is capable of steering and unclogging motions that improve its therapeutic maneuverability and functionality in human blood vessels. The tilting angle and vertical deflection of the catheter is described using the Euler-Bernoulli beam equation and defining two dimensionless variables. We also propose a methodology to precisely generate and control the steering and unclogging motions via a magnetic navigation system. We then conduct several experiments to show that the proposed system can control the vertical deflection, tilting angle, and drilling motion independently and effectively.

Torque Ripple and Unbalanced Magnetic Force of a BLDC Motor due to the Connecting Wire Between Slot Windings

In this research, the effect of the connecting wire between slot windings on the torque ripple and unbalanced magnetic force (UMF) of a brushless dc (BLDC) motor was investigated. A 2-dimensional finite element model of a BLDC motor that includes the effect of the connecting wires was also developed. It was found that the connecting wires generate pole harmonics in the torque ripple and UMF. Thus, a novel pattern of the connecting wire where all coils are located at rotationally symmetric positions is proposed in order to eliminate the pole harmonics of the torque ripple and UMF induced by the connecting wire. The experimental findings showed that the proposed pattern can effectively reduce the magnitude of the pole harmonics in the noise and vibration of a BLDC motor.