Gunhee Jang

Torque and unbalanced magnetic force in a rotational unsymmetric brushless DC motors

The pole-teeth-winding configuration in brushless dc motors determines torque and unbalanced magnetic force which are the resultants of the tangential and the normal magnetic force in a small air gap, respectively. This paper calculated torque and unbalanced magnetic force using FEM, Maxwell stress tensor to investigate the influence of pole-teeth-winding patterns on the performance from two common designs, i.e. the rotational symmetric 12-pole 9-tooth (12P9S) motor and the rotational unsymmetric 8-pole 9-tooth (8P9S) motor, and proposed the rotational unsymmetric 10-pole 9-tooth (10P9S) motor which achieves the high average torque of 12P9S motor and the low cogging torque of 8P9S at the same time. The analyses show that 8P9S and 10P9S motor tend to have less cogging torque because their bigger values of the least common multiple of pole and teeth reduce the cogging torque. The torque efficiency depends on pole-teeth-winding configuration. ABC-winding of 12P9S motor and three consecutive teeth winding of 10P9S motor utilize all six energized coil effectively to produce the high average torque. The normal magnetic force in a rotational unsymmetric design is not balanced and results in unbalanced magnetic force.

Magnetic Navigation System With Gradient and Uniform Saddle Coils for the Wireless Manipulation of Micro-Robots in Human Blood Vessels

A magnetic navigation system (MNS) for the wireless manipulation of micro-robots in human blood vessels is a possible surgical tool for coronary artery disease. This paper proposes a novel MNS composed of one conventional pair of Maxwell and Helmholtz coils and one newly developed pair of gradient and uniform saddle coils. The proposed system was theoretically developed using the Biot-Savart law, and it was verified experimentally after constructing the proposed MNS. The proposed MNS is geometrically compact to allow a patient to lie down, and magnetically efficient compared with the conventional MNS which has two pairs of Maxwell and Helmholtz coils.

Finite-element analysis of an electromechanical field of a BLDC motor considering speed control and mechanical flexibility

This research presents a finite-element analysis of the electromechanical field of a BLDC motor considering speed control and mechanical flexibility. The magnetic field is analyzed by the nonlinear time-stepping finite-element method considering the switching action of the pulse width modulation (PWM) inverter. Magnetic force and torque are calculated by the Maxwell stress tensor. Mechanical motion of a rotor is determined by a time-stepping finite-element method considering the flexibility of shaft, rotor, and bearing. Both magnetic and mechanical finite-element equations are combined in the closed loop to control the speed using PWM. Simulation results are verified by the experiments, and they are in good agreement with the experimental results.

Reduction of the Torque Ripple and Magnetic Force of a Rotatory Two-Phase Transverse Flux Machine Using Herringbone Teeth

The transverse flux machine (TFM) is a promising driving machine, especially for the low-speed applications, because it has greater power density, torque, and efficiency than the conventional electrical motors. However, the TFM has a complicated structure, a large torque ripple, and, occasionally, an unbalanced magnetic force. This paper investigates the effects of teeth geometry on torque ripple and unbalanced magnetic force in a rotatory two-phase TFM using the 3-D finite element method, and proposes a rotatory two-phase TFM with herringbone teeth to reduce the torque ripple and eliminate the unbalanced magnetic force.

Development of an axial-gap spindle motor for computer hard disk drives using PCB winding and dual air gaps

Summary form only given. This paper introduces the design and development of an axial-gap spindle motor using printed circuit boards (PCBs) and dual air gaps, which meet the mechanical rigidity, high efficiency and zero cogging torque required in a computer hard disk drive. Performance of the developed motor is experimentally compared with the conventional radial-gap spindle motor. Experimental results show the possibility that the developed motor can be used effectively for various disk drives with manufacturing flexibility.

A bipolar-starting and unipolar-running method to drive a hard disk drive spindle motor at high speed with large starting torque

This paper presents a method to drive a hard disk drive (HDD) spindle motor at high speed with large starting torque by utilizing a bipolar-starting and unipolar-running algorithm. It proposes a novel inverter circuit to switch from bipolar to unipolar drive, or vice versa. It also develops a digital signal processor (DSP)-based brushless dc (BLDC) motor controller not only to drive the BLDC motor with the bipolar or unipolar method, but also to switch from one method to the other at any speed. Torque-speed-current curves of a BLDC motor driven by bipolar or unipolar method are investigated experimentally, and the effectiveness of the proposed method is also verified by using the developed controller experimentally. This research shows that the proposed method starts the BLDC motor with large starting torque that can be obtained by a bipolar drive, and it runs the BLDC motor at high speed that can be driven by unipolar drive.

Performance Of A Brushless DC Motor Due To The Axial Geometry Of The Permanent Magnet

This paper investigated the skewing effect of the permanent magnet through three dimensional finite element analysis of a brushless DC motor, the principle of virtual work and Maxwell stress tensor by analyzing the mechanism and the characteristics of the production of the torque and the unbalanced magnetic force in the axial direction. It also suggested the novel shape of a herringbone magnet which increases the torque efficiency when rotated only in one direction. Skew magnets reduce the cogging torque by canceling the tangential force from the upper and the lower magnet because it has an anti-symmetric structure of permanent magnet with respect to the mid-plane. They produce the unbalanced magnetic force in the axial direction. However, herringbone magnets produce the increased cogging torque in any position due to the symmetry of the permanent magnet with respect to the mid-plane, which results in the large commutation torque. They do not produce the unbalanced magnetic force in an axial direction.

Prediction of the electromechanical faults in a single phase squirrel cage induction motor

In this paper, we characterizes how broken rotor bars and rotor eccentricity affect the electromechanical parameters such as input current, magnetic force and vibration of a rotor in order to effectively diagnose the faults of a single phase squirrel cage induction 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.

Development of a highly efficient hard disk drive spindle motor with a passive magnetic thrust bearing and a hydrodynamic journal bearing

This article presents a highly efficient hard disk drive (HDD) spindle motor with a passive magnetic thrust bearing and a hydrodynamic journal bearing. It eliminates the mechanical friction loss of a thrust bearing which is around 14% of total power consumption of a 3.5 in. HDD spindle motor, by replacing a conventional hydrodynamic thrust bearing with a passive magnetic thrust bearing. The passive magnetic thrust bearing using permanent magnets is inherently unstable in radial direction. However, the radial hydrodynamic force of the hydrodynamic journal bearing counterbalances the radial magnetic force of magnetic thrust bearing to achieve the stability as the motor spins up. Numerical analysis is performed to verify feasibility of the proposed system.