J. T. Li

Analytical Solution of Air-Gap Field in Permanent-Magnet Motors Taking Into Account the Effect of Pole Transition Over Slots

We present an analytical method to study magnetic fields in permanent-magnet brushless motors, taking into consideration the effect of stator slotting. Our attention concentrates particularly on the instantaneous field distribution in the slot regions where the magnet pole transition passes over the slot opening. The accuracy in the flux density vector distribution in such regions plays a critical role in the prediction of the magnetic forces, i.e., the cogging torque and unbalanced magnetic pull. However, the currently available analytical solutions for calculating air-gap fields in permanent magnet motors can estimate only the distribution of the flux density component in the radial direction. Magnetic field and forces computed by the new analytical method agree well with those obtained by the finite-element method. The analytical method provides a useful tool for design and optimization of permanent-magnet motors.

Accurate Prediction of Magnetic Field and Magnetic Forces in Permanent Magnet Motors Using an Analytical Solution

This paper presents an analytical model suitable for analyzing permanent magnet motors with slotted stator core. By including the effect of the interaction between the pole transitions and slot openings, the model is able to predict the airgap field and magnetic forces with high accuracy, which cannot be achieved using the previously available analytical methods. The results of electromagnetic forces, i.e., the cogging torque and unbalanced magnetic pull, computed analytically agree well with numerical simulations using the finite-element method. The model is used to analyze the magnetic forces developed in permanent magnet brushless motors when the design parameters vary in wide ranges. The model is useful in design and optimization of permanent magnet motors.

Effect of Radial Magnetic Forces in Permanent Magnet Motors With Rotor Eccentricity

This paper studies radial magnetic forces developed in permanent magnet motors having rotor eccentricity. Such forces represent the source of magnetically induced vibration in a disk-spindle assembly, and are of concern in design stage. A new analytical model suitable for studying the relationship between eccentricity effect and design parameters of slotted permanent magnet motors is introduced. The effectiveness of the model to study the effects of the rotor eccentricity and other leading design parameters is demonstrated through comparisons with numerical simulations

Design optimization for cogging torque minimization using response surface methodology

This paper discusses the application of response surface methodology (RSM) to design optimization for brushless dc permanent magnet motors for a hard disk driver to reduce cogging torque. The feasibility of using RSM with the finite-element method in practical engineering problems is investigated with computational examples and comparison between the fitted response and the results obtained from an analytical solution.

An improved analytical solution for predicting magnetic forces in permanent magnet motors

This paper describes an analytical model for analyzing magnetic forces developed in permanent magnet motors of radial field topology. The slotting effect is taken into consideration by solving the boundary value problem of the air gap field. The solution is expressed in the form of Fourier series with which the analysis of the harmonic contents in the magnetic forces can be readily performed. In particular, the curvature effect or the flux focusing effect in the slot opening regions is taken into consideration. The results of magnetic forces obtained from this model are verified with numerical simulations using the finite element method and experimental results.

Cogging torque prediction by superposition of torque due to pole transition over slot

In this paper, an effective method for predicting cogging torque developed in high precision permanent magnet motors used in data storage devices is presented. The torque component due to transition of magnet polarity over slot opening is studied in details, numerically and analytically, to gain in depth understanding of the torque development mechanism. The resultant cogging torque has good agreement with numerical simulation by finite element methods

Prediction and analysis of magnetic forces in permanent magnet brushless dc motor with rotor eccentricity

In design of permanent magnet motors for high-precision applications, it is sometimes necessary, early in the design stage, to have a detailed analysis of the effect of rotor eccentricity that may result from manufacturing imperfectness or use of fluid dynamic or aerodynamic bearings. This paper presents an analytical model for electromagnetic torque and forces in permanent magnet motors with rotor eccentricity. The model gives an insight to the relationship between the effect of the eccentricity and the other motor design parameters on the electromagnetic forces. It is shown that the calculated magnetic forces obtained from this model agree well with those obtained from numerical simulations that are very computationally demanding.

Dynamic simulation of high-density perpendicular recording head and media combination

This paper presents numerical simulation of high-density magnetic recording process with perpendicular head and media. The simulation is based on three-dimensional micromagnetic model of the media and an analytical model of the single pole perpendicular recording write field. The physical problem is modeled with a hybrid FEM-BEM formulation and the evaluation is accelerated using a new Fast Fourier Transform on Multipoles method. The model is suitable for studying magnetization transition configuration in perpendicular media with softmagnetic underlayer, and in turn can be used to derive microtrack model for evaluating the performance of recording systems

Direct Solution of Medium Field and Cross-Track Characteristics of Read Sensors

This paper describes a direct calculation method for medium fields in perpendicular recording systems. The method accounts for the effect of the zig-zag transition in the written medium pattern which can be obtained using micromagnetic simulations. The described method is useful for studying the cross-track characteristics of read sensors. The method is able to deal with a recording medium layer with nonunity relative permeability. The computed medium field in the gap region under the read head is compared with that obtained using the finite-element method. The purpose of this study is to develop a fast and effective tool for producing read-back signals based on computer modeling and simulationIn this paper,a direct calculation method for the medium field of perpendicular media is presented.The method accounts for the effects of the zig-zag transitions of the written medium pattern(which can be obtained from micromagnetic simulations),and other parameters.

3D Analysis of Medium Field with Consideration of Perpendicular Head-Medium Combinations

This paper describes the comparison of the micro-grid method and a 3D FEM for predicting the medium field in perpendicular recording systems. The microgrid method uses Fourier series expansion to simulate the three dimensional (3D) field emanated from the perpendicular medium under the air bearing surface (ABS) of the read sensor. The proposed method can account for the effect of the recorded transitions (in downtrack direction) and track edge effect of neighboring recorded tracks (in crosstrack direction). The described method is particularly useful for the reconstruction of the playback waveforms of a large number of recorded transitions. Computed medium field in the gap region under the read head agrees well with numerical simulations using 3D finite element method (FEM). The purpose of this study aims at validating a developed model for generation of playback signals with consideration of varying perpendicular head-media combinations