Der-Ray Huang

Simulation Study Of The Reduction Of Cogging Torque In Permanent Magnet Motors

The reduction of cogging torque in permanent magnet motors has been studied by varying the geometry shape of the saliencies of the armature core on stator of a 12-pole 9-tooth spindle motor. Mechanism of this reduction is explained by the minimum net integral of the product of normal and tangential magnetic flux with respect to the mechanical angle between the stator and rotor.

Theoretical computations for the torque of magnetic coupling

The torque of magnetic coupling with different magnetic poles has been investigated by theoretical computations with both FEA and torque formula techniques. The torque of magnetic coupling is sensitive to the number of magnetic poles, and it decreases with increasing the distance between the magnetic rings. From our theoretical computations, we find that we can increase the torque by increasing the number of poles for magnetic coupling between magnetic rings with short distance; however, this is not true for magnetic rings with large separation. We also demonstrate that the theoretical computations of both MagNet software and torque formula established by Furlani (1993) are quite consistent and useful for computing the torque of various magnetic couplings. Finally, the theoretical calculation has been successfully tested by using an experimental data taken from a NdFeB magnetic coupling. >

Design of a voice coil motor used in the focusing system of a digital video camera

This paper raises a valid method to design a voice coil motor (VCM) used in the focusing system of a digital video camera (DVC). A better VCM performance, such as lower battery consumption, higher efficiency, and shorter focusing time, can be achieved by turning the diameter of a winding coil, the thickness of the magnet, and the winding spaces in a VCM.

Cogging torque reduction of a single-phase brushless DC motor

In this research, the cogging torque of a newly designed single-phase brushless DC motor used in CD-ROM application is investigated. A finite element method is employed to numerically analyze the magnetic field distribution inside the motor, in which a three-dimensional mesh is constructed. The torque due to the magnetic coupling between the rotor and stator is estimated based upon the virtual work concept. It is proposed in this paper that the salient pole be divided into several regions in the azimuthal direction. By properly choosing the radii for these regions, the cogging torque can be greatly reduced.

Simulation study of the magnetic coupling between radial magnetic gears

The torque of magnetic coupling with different magnetic poles has been investigated by theoretical computations with two dimensional modeling processes of finite element analysis. The torque is sensitive to the number of magnetic poles, the material of the magnetic gears, and the distance between the magnetic gears. For a 2 mm separation distance of two magnetic gears with 20 mm radius, the maximum torque occurs between 6 and 20 poles which is dependent on the thickness of the iron yoke inside the magnets, and on the magnetization configuration within a pole of the magnets. This is explained by analyzing the magnetic coupling strength of each pole. Finally, the computer calculation is tested using an experimental data taken from a sintered NdFeB magnetic gear.

The radial magnetic coupling studies of perpendicular magnetic gears

The torque of the radial magnetic coupling between perpendicular magnetic gears with different magnetic poles has been investigated experimentally. The torque of magnetic coupling decreases with increasing the distance between the magnetic gears. For different multipole magnetic couplings with the same magnetic field strength, the torque of magnetic coupling increases as the number of magnetic poles increases for distances smaller than a critical separation distance d/sub c/, but it is reversed as the separation distance becomes larger. This critical separation distance for our sintered NdFeB magnet system with an iron yoke of 2 mm thickness is roughly between 9 and 11 mm. This phenomenon is explained by analyzing the magnetic coupling strength of different poles of magnets on the perpendicular magnetic gears.

Magnetic coupling studies between radial magnetic gears

The torque of a magnetic gear system with different magnetic poles has been investigated by computer-aided simulation with 2 dimensional modeling processes of finite element analysis. With a fixed separation of distance, the torque shows a maximum for a special number of poles, which shifts to a higher number of poles as the ratio of the radius to the thickness of the magnets increases and shifts to a lower number of poles with addition of an iron yoke. Using this technique, we can obtain an optimum design of a radial magnetic gear system for practical usage.

A new type single-phase spindle motor for HDD and DVD

The cogging torque and dynamic performance of a newly designed single phase brushless DC motor have been investigated in this paper. The single phase brushless spindle motor is usually applied for cooling fan, pump and blower before the performance is improved by the reengineering process. The stator configuration and the drive circuit have been remodeled in order to meet the requirements of the spindle motor used in the DVD and HDD applications. The cogging torque is reduced to 18 g-cm by the salient pole reshaping. An automatic phase adjuster is also introduced to improve the performance of the dynamic characteristics of a single phase spindle motor in this paper. According to the test results, the maximum speed could be increased from 6500 rpm to 12000 rpm and the efficiency from 22% to 38%. A single phase motor has been demonstrated successfully in HDD and DVD applications by reshaping for the salient pole and phase adjusted automatically with the rotation speed.

Low power consumption focusing actuator for a mini video camera

A novel low power consumption autofocusing actuator in a mini video camera is constructed in accordance with the result of a systematic design procedure of voice coil motors (VCM). This paper emphasizes the position control of such a VCM. The position feedback signals are provided by a magnetoresistive (MR) encoder. The position estimation algorithm (PEA) is developed to precisely decode the MR signals for the position of the moving part of the VCM. Different postures change the loading of the moving part of the VCM, so that an adaptive model-following control system based on the PEA is proposed to compensate for the loading variation. The experiments verify the fast dynamic performance and high power efficiency of the VCM.

Kinetic Crystallization Behavior of Phase-Change Medium

The crystallization behavior of nominal-composition GeSb2Te4 films prepared by rf-magnetron sputtering are examined. The crystal structures of the as-sputtered and the annealed films at different annealing temperatures are identified by the X-ray diffraction (XRD) method. Two phase transformations occur in the conventional slow heating process when the as-sputtered film is heat-treated from the ambient temperature to its melting point. However, only the amorphous to face-centered cubic (FCC) transformation is allowed when laser annealing with a 1011°C/min heating rate is applied to heat the films. Consequently, we predict that the meta stable FCC phase, instead of the hexagonal closed-packed (HCP) phase, is the dominant crystalline phase in the GeSb2Te4 phase-change recording medium.