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.     

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.     

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.     

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.     

Compensation of torque ripple in high performance BLDC motor drives

Brushless DC motor drives (BLDC) are finding expanded use in high performance applications where torque smoothness is essential. The nature of the square-wave current excitation waveforms in BLDC motor drives permits some important system simplifications compared to sinusoidal permanent magnet AC (PMAC) machines. However, it is the simplicity of the BLDC motor drive that is responsible for causing an additional source of ripple torque commonly known as commutation torque to develop. In this paper, a compensation technique for reducing the commutation torque ripple is proposed. With the experimental results, the proposed method demonstrates the effectiveness for a control system using the BLDC motors that requires high speed and accuracy.     

永磁无刷电机方波和正弦波驱动的转矩研究

使用电磁场分析软件和Matlab/Simulink仿真工具,分别对永磁无刷电机方波和正弦波驱动时的稳态电磁转矩和动态电磁转矩进行了仿真分析,对两种驱动方式下的稳态电磁转矩的大小、转矩脉动进行了比较。结果表明,正弦波驱动较方波驱动稳态电磁转矩值及转矩脉动减小,动态电磁转矩脉动频率增加,但脉动幅值也同时增加。     

An effective method to obtain commutation positions in BLDC drive mode

The widely adopted drive method for the spindle motors with sinusoidal back-EMF in hard disk drive is to inject current into two phases and use the third phase to detect the rotor position. The commutation position to switch phases is normally 30 electrical degrees after the zero crossing points (ZCPs) of the silent phase back-EMF. To minimize the current ripple and thus the torque ripple, the commutation positions should be accurate and less prone to ZCP jitters. In this paper, an effective method based on the flux-linkage increment (FLI) is presented to realize accurate and robust commutation position detection. This method can greatly reduce the commutation position jitter even with obvious ZCP error. Experimental results show that the FLI method work well over a large speed range.     

Development and optimal design of a HDD spindle motor with pulling magnet to reduce electrical loss

A conventional hard disk drive (HDD) spindle motor has a pulling plate to generate the axial magnetic force. However, the pulling plate consumes significant amount of iron loss due to the alternating magnetic field on the pulling plate. We propose the new design of a HDD spindle motor with pulling magnet to generate the pre-load as well as to eliminate the iron loss of the pulling plate. We also develop an optimal design methodology to minimize iron and copper losses from the spindle motor of a computer HDD while maintaining the same level of torque ripple and pulling force. The new design is optimized by the developed optimal design methodology. A metamodel is constructed from the three-dimensional finite element analysis of the magnetic field and the meta-modeling techniques, and the accuracies of the metamodels are discussed. The proposed optimal design problem is solved by the progressive quadratic approximation method. The proposed design reduces the electrical loss of the HDD spindle motor by 30.42?% while maintaining the same level of torque ripple and pulling force.     

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     

Vibro-acoustic interaction of components in hard disk drive under seek process

With the increasing use of electro-mechanical systems such as hard disk drives, CD-Rom drives, and DVD drives in the consumer electronics industry, there is a growing demand for quieter products. The noise emitted from these devices may originate from the vibration of mechanical components in operation, such as bearings, gears and actuators. The vibration is then transmitted to other parts of the devices, such as the cover, and the noise emitted may then be amplified. This paper aims to develop a method for identify the acoustic noise emitted from hard disk drive seek process. In order to determine effective noise and vibration control of seek noise during the seek process, we first investigate the dynamic characteristic of the head actuator assembly under the different electrical drive signal using finite element method. In this paper, a bearing stiffness matrix (6 × 6) is adopted and performed using ANSYS element (Matrix 27). Using this method, we can understand the vibro-acoustic characteristics of hard disk drives and their components, and the mechanisms of vibration and sound transmission. Experiments are being conducted to demonstrate its validity through experiments. The method will also enable design optimisation for noise to be carried out at the design stage, before a new product is built, or help guide design changes on an existing device.Paper presented at the 13th Annual Symposium on Information Storage and Processing Systems, Santa Clara, CA, USA, 17–18 June, 2002     

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.

     

Effects of temperature on particle trajectories inside hard disk drives

The presence of particles, which can intrude into the gas bearing, is one of the most common factors in the failure of hard disk drives (HDDs). Previous works investigated particle trajectories inside air-filled drives without considering temperature effects on the distribution of particles. Actually, especially for the submicron particle, particle trajectories and trapping status are affected by the temperature gradient since the thermophoretic force cannot be ignored. In this paper, considering major heat generation components such as the spindle motor and voice coil motor (VCM), trajectories and trapping status for Al₂O₃ particles inside a 2.5 inch helium-filled drive are simulated by the commercial computational fluid dynamics solver FLUENT with user-defined functions (UDFs). The trapping criterion for Al₂O₃ particles is used as boundary conditions for different colliding surfaces. The results reveal that particles in the air-filled drive will more likely degrade the head–disk interface (HDI) reliability. In addition, after considering the temperature, the particle trapping rate by the disk decreases both inside the air-filled drive and the helium-filled drive. And its reduction inside the air-filled drive is larger. Moreover, small particles will more likely degrade the HDI reliability since they can follow the rotatory flow well and have more chance to collide with the disk surface, and then easily attach onto the disk surface.

     

Modeling of a synchronous reluctance machine accounting for space harmonics in view of torque ripple minimization

The paper deals with modeling of synchronous reluctance motor (SynRM) accounting for all phenomena responsible for torque ripple. Based on winding function approach, the proposed model consists in computing self and mutual inductances considering no sinusoidal distribution of stator windings, slotting effect and no sinusoidal reluctance variation caused by the rotor saliency. Then, optimal current waveforms are determined for each rotor position by solving a second order equation to reduce torque ripple. These currents are used within a vector control scheme. Satisfactory agreement between simulation and experimental results is obtained.     

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.     

A study of non-operational dynamic responses of disk in 3.5 in. hard disk drive to impact load

Hard disk drives have to be designed to sustain operational and non-operational shock. There are many analytical models and numerical schemes proposed and many experiments conducted for analyzing the transient impact responses of hard disk drives. The existing researches have been focused on the slider-suspension responses at the head-disk interface in which the linear models have been used and the effects of spindle motor have been ignored. In this study, the complex vibrations of disk of 3.5 in. hard disk drive (HDD) under shock are experimentally investigated. The hammer impact test and linear drop test are conducted for the HDD to study the effect of shock on the disk responses. The results show that the nonlinear rock modes substantially contribute to the vibrations of disk when HDD is under shock impact. The nonlinear properties of the disk responses and the mode damping ratio are evaluated by using empirical mode decomposition approach.     

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.     

On investigation of vibro-acoustics of FDB spindle motors for hard disk drives

The present work investigates vibro-acoustic behaviors of the fluid dynamic bearing (FDB) spindle motors for hard disk drives (HDD) through the sound spectra and the frequency response functions (FRF) of the motor structure. The quantitative evidence on the significance of the acoustic noise originated from the electromagnetic source is deduced from the sound spectra that were measured in two distinct cases of the spinning motor: in the normal operation and at the moment immediately after the power supply was disconnected. It is found that the effect of electromagnetic noise source is more dominant than the combined effect of the mechanical and aerodynamic sources. In addition, it is identified that, within the audible range of frequency, the frequency range of 13.4–20 kHz deems important to the noise problem as it is the main contributor to the acoustic noise for the FDB spindle motors. Moreover, the structural resonances that can be identified via the FRF are found to play an important role in the noise emitted by the motors. The concurrence of resonance and excitation frequencies clearly intensifies the sound spectrum, resulting in high discrete peaks, hence higher decibel level.     

Voltage driven hard disk drive with voice coil model-based control

In this paper, we describe a new solution for driving the voice coil motor (VCM) in hard disk drives (HDDs), in which the usual current driver for the voice coil motor has been replaced by a voltage driver. When used in conjunction with PWM power stages, this solution becomes fully digital and has proven advantages in terms of cost, power dissipation and silicon area. To achieve the same performance of the current driver, the voltage driver requires a pre-filter placed at its input, to cancel out the electrical pole of the VCM. In the paper, we describe the voice coil model-based control (VCMC), a solution for implementing the pre-filter, which replicates the behavior of a current loop by using a model of the voice coil motor and its driver, including the saturation of the power stage. It is worth noticing that VCM resistance may change by 30% during HDD operations, increasing when the disk is performing repetitive seeks or decreasing when the disk cools down during track following. Such variation may lead to an unsatisfactory performance of the VCMC, so an adaptation mechanism, capable of tracking variations of VCM coil resistance, must be set up. This paper presents a pair of on-line estimation procedure, used to get the value of the VCM coil resistance during seek and track following, respectively. The first one is based on a standard LMS approach, aimed at identifying a simplified model of the plant with the least computational effort. The second exploits the presence of repetitive disturbances (RROs) to detect variations of plant gain and, in turn, of VCM resistance. It will be shown that both procedures are quite accurate in estimating variations of VCM resistance and their output can be used to perform on-line tuning of the VCMC. Experimental results show that the servo performance with the adaptive VCMC is not affected by resistance variation and equivalent to that of the standard current driver.     

具有死区补偿的自抗扰控制下PMSM转矩脉动抑制方法

空间矢量脉宽调制死区效应对永磁同步电机(PMSM) 的调速控制系统及转矩脉动有一定影响, 为了削弱其不利作用, 在永磁同步电机矢量控制基础上, 提出一种新型的具有死区补偿的自抗扰PMSM控制方案, 针对传统自抗扰控制策略下电机转矩脉动较大的缺陷, 在原有的自抗扰控制策略中加入死区补偿. 仿真及实验结果表明, 具有死区补偿的自抗扰PMSM驱动系统, 谐波含量明显减少, 速度驱动系统更加平稳, 有效抑制了转矩脉动.

     

内置式永磁同步电机低噪声控制策略研究

针对采用最大转矩电流比控制策略的内置式永磁同步电机,由于受到电流谐波的影响,导致其径向电磁力成分复杂和越来越突出的电机振动噪声问题,从考虑电流谐波影响的径向电磁力产生机理出发,提出一种基于谐振调节器的电机噪声抑制的方法。该方法根据谐振调节器在特定谐振频率处的增益为无穷大,结合PI调节器可以较好地抑制电流谐波,削弱径向电磁力,降低内置式永磁同步电机的振动噪声。仿真实验结果表明,所提方法能够有效地削弱电磁径向力,降低电机振动噪声。