Development of a new spindle motor for a hard disk drive

A new spindle motor is developed with a sloped permanent magnet (PM) for a hard disk drive (HDD). In a conventional spindle motor, a pulling plate is installed at the stationary part under the rotating PM to pull down rotating bodies. This axial force is required for stable operation of the spindle motor using a hydrodynamic bearing. However, the pulling plate has considerable iron loss and a negative torque opposing the direction of rotation due to the induced eddy currents. Our proposed model has a sloped PM surface to generate the required axial force as well as torque without the pulling plate. Optimal design is carried out by a response surface methodology, and the new spindle motors are prototyped. The resulting electrical and mechanical performance of the prototyped motors is compared with that of conventional models, showing the possibility of adapting the proposed model for an HDD spindle motor.     

Robust optimal design of a magnetizer to reduce the harmonic components of cogging torque in a HDD spindle motor

This research proposes a robust optimal design methodology to reduce the cogging torque of a hard disk drive (HDD) spindle motor due to the coil-positioning error of the magnetizer. The design optimization problem of the magnetizer is formulated with an objective function of the cogging torque and the constraints of the torque constant. The coil-positioning errors measured by computerized tomography are considered as the random variables of the robust optimal design problem. Additional design variables of the magnetizer are chosen in the optimization problem, such as back-yoke thickness, notch depth, etc. Magnetic finite element analysis of the HDD spindle motor is also performed to calculate the cogging torque and torque constant. The cogging torque and torque constant of the optimal design are compared with those of the conventional design, demonstrating that the proposed method effectively reduces the cogging toque of the HDD spindle motor.     

Noise and vibration due to rotor eccentricity in a HDD spindle system

This paper numerically and experimentally investigates the characteristics of torque ripple and unbalanced magnetic force (UMF) due to rotor eccentricity and their effects on noise and vibration in a hard disk drive (HDD) spindle motor with 12 poles and 9 slots. The major excitation frequencies of a non-operating HDD spindle system with rotor eccentricity are the least common multiples (LCM) of pole and slot numbers of the cogging torque and the harmonics of slot number ±1 of the UMF. An experimental setup is developed to measure the UMF generated by rotor eccentricity and to verify the simulated UMF. In the operating HDD spindle motor, the harmonics of the commutation frequency of torque ripple (multiplication of pole and phase) are increased by the interaction of the driving current and rotor eccentricity, and they are the same as the LCM of pole and slot numbers for a HDD spindle motor with 12 poles and 9 slots. The major excitation frequencies of the UMF while operating condition are also the harmonics of slot number ±1 and the harmonics of commutation frequency ±1. We verify that the source of the harmonics of slot number ±1 and the harmonics of commutation frequency ±1 in acoustic noise and vibration is rotor eccentricity of the UMF through experiments.     

Analysis of PDT noise originating from driving method of a HDD spindle motor

This paper investigates the prominence discrete tone (PDT) noise originating from the driving method of a hard disk drive (HDD) spindle motor with 12 poles and 9 slots. Torque ripple of a HDD is reconstructed by the multiplication of measured back electromotive force (BEMF) and measured switching current. It shows that the frequency components of PDT noise match with those of torque ripple. It also investigates the frequency change of PDT noise due to two driving methods which have the different switching-off periods to detect the zero-crossing of the BEMF. The BEMF has odd harmonics of the number of pole pair, but the current has even harmonics of the number of pole pair due to the switching-off period as well as those odd harmonics of BEMF. We theoretically derive the torque equation in terms of the frequency components of BEMF and switching current. We also verify that the even harmonics of the driving current due to driving method generate the 54th harmonic of torque ripple, and show that the pure sinusoidal BEMF with the 6th harmonic can decrease the 36th harmonic of torque ripple as well as PDT noise in the HDD spindle systems.     

A study of acoustic noise generating mechanisms of small form factor HDDs

A combined experimental and numerical study of the acoustic noise from a small form factor hard disk drive (HDD) is made to investigate the relative contribution of structure-borne idle noise to the total generated noise. Initially, the idle noise of a 1.8″ HDD was measured in an anechoic chamber, and a clear high-frequency peak is found in its total idle noise frequency spectrum. Then the modeling and simulation (M&S) of the top cover vibration and the associated sound radiation are performed to identify the dominant source and transmission path causing this noise peak. The M&S process consists of a 3D structural finite element (FE) modeling of the HDD to calculate the frequency-domain vibration response of the top cover, and a boundary element (BE) modeling of the HDD for calculating the radiated sound pressure. The loading specified in the FE model is motor torque ripple: the dominant electromagnetic excitation of fluid dynamic bearing spindle motor for HDDs. Finally, the obtained acoustic BE results of the sound pressure levels at a selected field point are compared to those measured physically in the chamber. It is shown that for the HDD considered, the coincidence of a high-frequency resonant mode with the fifth harmonic frequency of motor torque ripple is responsible for the high-frequency peak noise in the idle noise spectrum.     

Investigation of the electromechanical variables of the spindle motor and the actuator of a HDD due to positioning and free fall

This research investigates the electromechanical variables of a spindle motor and an actuator of an operating hard disk drive (HDD) due to the positioning and the free-fall of a HDD. Magnetic fields of a brushless DC motor and a voice coil motor are determined by the time-stepping finite element equation of the Maxwell equation and the driving circuit equation. The pressure of the fluid dynamic bearings (FDBs) is determined by solving the finite element equation of the Reynolds equation to calculate the reaction force and the friction torque. Dynamic equations of the rotating disk-spindle, actuator, and stationary bodies of a HDD are derived from the Newton–Euler’s equation. The speed control of the rotating disk-spindle and the servo control of the actuator are included to describe the head positioning between the rotating disk and the head. The simulation is performed to investigate the electromechanical variables of the spindle motor and the actuator due to the positioning and the free-fall of a HDD. This research shows that the positioning and the free-fall of a HDD change the electromechanical variables of the spindle motor and the actuator of an operating HDD, and that monitoring their electromechanical variables may identify the positioning and the free-fall of a HDD without using extra sensors.     

Improvement of dynamic characteristics of a HDD spindle system supported by ball bearing at elevated temperature

This research investigates how the design variables of ball bearing affect the bearing stiffness and the natural frequencies of a hard disk drive (HDD) spindle system at elevated temperature. It shows that any design change that increases the contact angle of ball bearing reduces the variation in the bearing stiffness and the natural frequencies at elevated temperature. This research also proposes a robust HDD spindle motor in which a wave spring maintains a constant preload minimizing the effect of temperature variation. Experimental modal testing shows that the reduction of the natural frequencies at elevated temperature is much less in the proposed HDD spindle system than in the conventional spindle system. The proposed HDD spindle motor can improve the dynamic reliability of a HDD spindle system, which contributes to the high track density of a HDD.     

Magnetically induced vibration of a flexible rotating disk-spindle system due to the internal magnetic force arising from the spindle motor of a HDD

This paper investigates the magnetically induced vibration of a flexible rotating disk-spindle system and stationary stator-base due to the internal excitation of the local magnetic force arising from the spindle motor of a HDD. A three-dimensional magnetic finite element model of the spindle motor is developed, and the Maxwell stress tensor method is applied to calculate the local magnetic force acting on the stationary teeth and rotating permanent magnet of the spindle motor. Also, a three-dimensional structural finite element model is developed and local magnetic force is applied to teeth and permanent magnet. The simulated forced vibration of the base plate matched well with the measured one. The dominant frequency component of local magnetic force is the 12th harmonic corresponding to the number of poles, but the dominant frequency component of vibration is the 36th harmonic corresponding to the least common multiple of the number of poles and slots because the 12 and 24th harmonics in local force are canceled out when they are summed up along the air gap. The 12th, 24th and 36th harmonics of the axial vibration are mostly affected by the axial magnetic force, and the amplitudes of those harmonics are increased with the increase of stator eccentricity.     

Effect of an hourglass-shaped sleeve on the performance of the fluid dynamic bearings of a HDD spindle motor

This research investigated the characteristics of fluid dynamic bearings (FDBs) in a HDD spindle motor with an hourglass-shaped sleeve. We demonstrated experimentally that the hourglass-shaped sleeve generated through the ball-sizing process is a major source of large repeatable runout and non-repeatable runout in a HDD spindle system. We also numerically proved the effect of hourglass-shaped sleeves on pressure, friction torque, stiffness and damping coefficients, critical mass, and shock response. Finally, we proposed a robust design for FDBs with hourglass-shaped groove depths to compensate for the decrease in the static and dynamic performance of FDBs with hourglass-shaped sleeves. The proposed hourglass-shaped groove depth improves the performance of FDBs with both straight and hourglass-shaped sleeves.     

矿井提升机直接转矩控制系统转矩脉动最优控制

针对矿井提升机直接转矩控制系统低速段运行时存在转矩脉动过大的问题,提出了一种矿井提升机转矩脉动最优控制方法。该方法以预测模型为基础,采用零电压矢量注入方式进行最优电压矢量的占空比调整。整个占空比计算过程以转矩脉动最小为设计指标,采用在线计算的方式实时获得最优占空比。实验结果表明,该方法在低速时可有效减小电动机转矩脉动,获得优异的转矩控制性能。     

Whirling, tilting and axial motions of a HDD spindle system due to the manufacturing errors of FDBs

This paper investigates the whirling, tilting and axial motions of a hard disk drive (HDD) spindle system due to manufacturing errors of fluid dynamic bearings (FDBs). HDD spindle whirls around the sleeve with tilting angle due to the centrifugal force of unbalanced mass and the gyroscopic moment of rotating spindle in addition to axial motion. The whirling, tilting and axial motions may be increased by the manufacturing errors of FDBs such as imperfect cylindricity of sleeve bore, or imperfect perpendicularity between shaft and thrust plate. They increase the disk run-out to limit memory capacity and they may result in the instability of the HDD spindle system. This paper proposes the modified Reynolds equations for the coupled journal and thrust FDBs to include the variable film thickness due to the cylindricity of sleeve bore and the perpendicularity between shaft and thrust plate. Finite element method is used to solve the modified Reynolds equation to calculate the pressure distribution. Reaction forces and friction torque are obtained by integrating the pressure and shear stress, respectively. The whirling, tilting and axial motions of the HDD spindle system are determined by solving the equations of a motion of a HDD spindle system in six degrees of freedom with the Runge-Kutta method. It shows that the imperfect cylindricity and perpendicularity increase the whirl radius, axial runout and tilting angle of the HDD spindle system. However, the degradation of dynamic performance due to the imperfect perpendicularity between shaft and thrust plate can be improved by allowing the other manufacturing error of the cylindricity of sleeve bore in such a way to compensate the bad effect of the imperfect perpendicularity.     

磁悬浮硬盘中非记录磁场的研究

介绍了磁悬浮硬盘的概念，测量并分析了普通硬盘的音圈电机和主轴电机产生的非记录磁场以及磁悬浮硬盘中的磁力轴承产生的非记录磁场，分析了非记录磁场对记录磁场的影响，为磁悬浮硬盘的设计和研究提供了依据。     

Reduction of torque ripple and mechanical vibration of spindle motors in hard-disk drives using a sinusoidal driver

Mechanical vibration and acoustic noise are major obstacles in the development of high-density and high-spindle-speed hard disk drives. Torque ripple caused by the electrical driver is the main source of vibration and noise. This paper proposes a novel driver for spindle motors in hard disk drives based on the principle of position sensorless vector control. To reduce torque ripple, the proposed driver feeds the spindle motor in sinusoidal driving mode by which the sinusoidal current of the motor can be obtained. Experimental results of the proposed driver demonstrate the better driving performance in startup condition and fine sinusoidal current in steady state. Vibration testing shows significant improvement in the attenuation of vibration: the dominant vibration modes can be reduced to one tenth compared to that of a conventional driver. In addition, the mechanism of inducing torque ripple from time-harmonic currents is analyzed and the relationship between induced torque ripple and exhibited vibration modes is examined.     

Reduction of torque ripple and mechanical vibration of spindle motors in hard-disk drives using a sinusoidal driver

Mechanical vibration and acoustic noise are major obstacles in the development of high-density and high-spindle-speed hard disk drives. Torque ripple caused by the electrical driver is the main source of vibration and noise. This paper proposes a novel driver for spindle motors in hard disk drives based on the principle of position sensorless vector control. To reduce torque ripple, the proposed driver feeds the spindle motor in sinusoidal driving mode by which the sinusoidal current of the motor can be obtained. Experimental results of the proposed driver demonstrate the better driving performance in startup condition and fine sinusoidal current in steady state. Vibration testing shows significant improvement in the attenuation of vibration: the dominant vibration modes can be reduced to one tenth compared to that of a conventional driver. In addition, the mechanism of inducing torque ripple from time-harmonic currents is analyzed and the relationship between induced torque ripple and exhibited vibration modes is examined.

     

Motor noise generation and prediction for high spinning speed hard disk drive

The acoustic level of a hard disk drive is an important specification. This is especially so for enterprise HDD which is required to operate under a high spinning speed. In order to reduce the acoustics level of a HDD, an in depth understanding behind the mechanisms whereby the noise is being generated in a HDD should be established. This paper will study the acoustics characteristics of a high speed permanent magnet brushless DC motor (PM BLDC) and investigate the physics underlying the generation of noise associated with a motor. An analysis procedure of the PM BLDC motor noise generating mechanisms is proposed. Through finite element analysis and experimental verification, the results indicate that the major noise source for the high speed PM BLDC motor is due to the presence of electromagnetic (EM) torque ripples. Furthermore, it has been observed that the noise radiated by a HDD can be amplified when its structural dynamics are close to the frequency components of the noise source. Finally, a methodology which discusses the steps involved in the prediction of motor radiated noise will be presented.     

基于Magnet的六相感应电动机建模及仿真研究

在Magnet环境中建立六相感应电动机模型,并采用梯形波相电流对其驱动;分析了转矩电流和转子电流的关系,表明梯形波相电流实现了励磁电流和转矩电流的分立控制;对电磁场进行2D瞬态磁场仿真,分析了等磁势分布情况、磁感应强度波形、稳态电磁转矩和转矩电流的关系;添加Motion单元,对电动机的启动性能进行2D动态仿真。仿真结果表明,电动机空载和负载运行时电磁转矩响应速度快,无明显电磁转矩脉动和转速脉动,说明采用梯形波相电流驱动电动机的方法切实可行,仿真参数设置合理,为最终实现电动机的性能优化提供了参考。     

Dynamic analysis of a HDD spindle system with FDBs due to the bearing width and asymmetric grooves of journal bearing

This paper investigates the dynamic behavior of a HDD spindle system with fluid dynamic bearings (FDBs) by solving the Reynolds equation and the equations of a motion of a HDD spindle system in five degrees of freedom. FEM is used to solve the Reynolds equation in order to calculate the pressure distribution in fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors of a HDD spindle system, such as the whirling and the tilting motion, are determined by solving its nonlinear equations of motion with the Runge-Kutta method. This paper also proposes two design methods to improve the dynamic characteristics of a HDD spindle system without increasing friction torque, i.e., optimization of the width of the lower and the upper journal bearings and the journal bearings with asymmetric grooves.     

无刷直流电动机动态性能分析

针对无刷直流电动机实际运行过程中存在的脉动和非平滑现象,基于内部结构特征和工作原理,研究了无刷直流电动机的运动特征和动态特性.从电机齿槽结构、绕组形式、转子位置、换相过程等方面分析了气隙磁场分布特征和对相电流、反电动势波形的关联作用,阐述了造成转速变化和产生脉动转矩的影响机理,讨论了单闭环控制与双闭环控制方式下的电机运行特性.通过搭建系统仿真模型,获得了空载启动、突加负载、变转速等控制要求下电机转速、定子电流和转矩的运行曲线和变化规律.理论分析和仿真实验均有效地阐明了无刷直流电动机的动态性能.     

Commutation Torque Ripple Suppression in Three Phase Brushless DC Motor Using Open-end Winding

Three phase brushless DC motor has the characteristics of high power density, simple structure and excellent speed regulation performance, which is widely used in the field of electric drive. Open-end winding brushless DC motor has no neutral point, and each phase winding is electrically isolated, which can realize the independent control of each phase winding. Compared with Y-connected brushless DC motor, the open-end winding brushless DC motor has a wider range of speed regulation under the same voltage, and has certain fault-tolerant performance, which is suitable for the application of low voltage and large current. Compared with the multiphase fault-tolerant motor, open-end winding brushless DC motor has simpler structure and higher winding utilization rate. However, the open-end winding brushless DC motor still has torque ripple, among which the cogging torque is related to the motor body structure, while commutation torque ripple is affected by the mutual inductance of the winding and the current freewheeling loop. The commutation process of the open-winding brushless DC motor is analyzed, and it is concluded that the current change rates of the turn-off phase and turn-on phase are equal under the ideal back electromotive force(back-EMF), which can ensure that the non-commutation phase current and the electromagnetic torque kept constant. The overlapping commutation with phase current closed-loop method is proposed to suppress the commutation torque ripple of open-end winding BLDC motor, and the applied voltage on turn-off phase and delayed time of turn-off phase in overlapping commutation are derived, the sliding mode observer is used to calculate the electromagnetic torque. MATLAB simulation and experimental results verify the effectiveness of this method.

     

Transient dynamic analysis of ferro-fluid bearing spindle motor

 With areal recording density of hard disk drives (HDD) historically growing at an average of 60% per year and fast spindle speed to continue to reduce access time, it is becoming increasingly more difficult to maintain the precise positioning required of the GMR heads to read and write data. Any unexpected vibration will cause the data written to a wrong data track. Consequently, the dynamic behaviors of HDD spindle systems and their potential influences on track misregistration are key issues in disk drive design. With rapid advances in the emerging consumer device market, the fluid bearing spindle motors, which have low NRRO, low acoustic noise and high damping, are being developed as next generation spindles. This paper is to study transient dynamic performance of HDD ferro-fluid bearing spindle systems. The FEA based component mode synthesis method is used to reduce the overall spindle system dimensions. The effect of the unbalanced magnetic pulls (UMP) due to two different types of motor configurations (balanced and unbalanced configurations) on the dynamic behaviors of spindle system was investigated. The simulated results show that the motor with balanced configuration provides better spindle dynamic performance due to absence of UMP. The UMP derived from the unbalanced configuration can result in some frequency resonance interactions and adversely affect the HDD servo-tracking system. Received: 5 July 2001/Accepted: 17 October 2001