A novel contact slider/gimbal to raise recording density in flexible disk drives

 We developed the soft and full-contact head/gimbal assembly (HGA) for card-size flexible disk drive. We used a 150 μg slider and a flexible beam of BeCu alloy to realize soft contact. We designed our HGA using FEM simulation and optimized the load force, the load pressure, and the stress on the beam. We report the mechanical characteristics, read-write signals, and the vibration of the HGA. A new type loading/unloading mechanism was developed for the removable flexible medium, and confirmed the reliability of the loading/unloading mechanism by the deformation of the HGA and the loaded medium. Received: 5 July 2001/Accepted: 1 November 2001     

Non-operational shock analysis and design of head gimbal assembly in spinning data storage devices

The work presented in this paper was motivated by the experimental observation of de-bonding phenomena between head gimbal assembly (HGA) and suspension for a commercial 3.5-in. enterprise HDD under non-operational 250?G shock test, which leads to revisit design of HGA/suspension with objective placed on withstanding shocks between the head slider and the suspension. In this study experimental observation and numerical finite element studies were conducted to understand such effect on the mechanical failure of HGA when it is subjected to non-operational shock in parked position on ramp. It was observed that by changing flexure angle in HGA, shock stress can be reduced. FEA simulation results have been presented to verify the findings.     

Experimental study of slider�Cdisk interaction process with thermal-flying-height controlled slider

Thermal flying height (TFC) controlled slider has been introduced in hard disk drive recently. Flying height at the read/write elements of the slider is controlled by thermal pole tip protrusion. Interactions between the TFC slider and disk can be very gentle because the low flying height thermal protrusion area is usually very small. It is still a big challenge to detect very gentle interactions. In this work, a very sensitive method to study very gentle slider?Cdisk interaction in frequency domain has been developed and details of the TFC slider?Cdisk interactions from gentle to strong have been revealed. It is proved that higher heating power is required to initiate the vibration in which higher stiffness part of the slider air-bearing is involved.     

Position error reduction in magnetic disk drives using a head gimbal assembly with radial head motion capability

Reducing the head positioning error is important to achieve higher track density in hard disk drives. In this paper, it is shown that the head off-track due to disk vibration can be reduced by using a head gimbal assembly capable of moving not only vertically to disk surface but also radially across the track. We find the optimal geometric relationship to minimize the head off-track due to disk vibration. The relationship is obtained based on precise mathematical modeling of head off-track mechanism due to disk vibration. Some examples of head gimbal assembly (HGA) with radial head motion capability, which satisfy such optimal relationship, are also proposed. It is experimentally found that the proposed optimal HGA can reduce non-repeatable run-out (NRRO) position error signal (PES) significantly. Since it reduces NRRO PES during servo track writing as well, the written-in portion of repeatable run-out PES can be also significantly reduced.     

HAMR HDD shock responses

Heat assisted magnetic recording (HAMR) and slim mobile hard disk drives (HDD) are being developed parallelly to maintain cost advantage over the solid state drive. Operational shock and non-operational shock capabilities are seriously challenged for the slim HDDs due to reduced stiffness (thickness). It is worse for slim HAMR drives due to additional laser diode (LD) and other necessities being added on slider. Shock tests are part of the key performance matrices that must be passed in HDD reliability tests, and the concerns for HAMR mobile drives are, (1) slider lift-off G-level degradation during op-shock, and (2) LD back-to-back hitting during non-operational shock. We studied a few potential HAMR HGA designs, also analyzed a design that improves drive op-shock performances.     

Active-head sliders using piezoelectric thin films for flying height control

This paper describes design and fabrication of a MEMS-based active-head slider using a PZT thin film for flying height control in hard disk drives. A piezoelectric cantilever integrated in the air bearing slider is used to adjust the flying height individually. An air bearing surface (ABS) geometry that minimizes the aerodynamic lift force generated beneath the head has been designed based on the molecular gas film lubrication (MGL) theory. The sliders with PZT actuators were fabricated monolithically by silicon micromachining process. Performance of the actuator was tested by using an optical surface profiler. Furthermore, the fabricated slider was mounted on a suspension and the flying height of the slider above a spinning disk has been measured by multiple wavelength interferometry. Change in the head-disk spacing has been successfully confirmed by applying voltage to the actuator.     

Tri-state dynamic model and adhesive effects on flying-height modulation for ultra-low flying head disk interfaces

Physical spacing between a flying slider and a rotating disk is projected to be 3 nm in order to achieve extremely high areal recording densities of 1 Tb/in². In such ultra-low flying-height regimes, two imminent obstacles that need to be overcome are intermittent head/disk contacts and strong intermolecular adhesive forces at the head/disk interface (HDI). Head/disk contact can cause large vibrations of the recording slider and possibly damage the disk and slider due to large contact forces. Strong adhesive forces disturb the balance of forces in a flying slider by pulling it down onto the disk and increasing the possibility of catastrophic HDI failures by doing so. This paper describes a dynamic model that includes contact and adhesive forces. Specifically, a lumped parameter single degree-of-freedom, three state nonlinear dynamic model representing the normal dynamics of the HDI and asperity-based contact and adhesive models were developed and coupled together to predict the performance of ultra-low flying sliders. The validity of the proposed dynamic model was confirmed in terms of flying-height modulation (FHM) by experimental measurements using ultra-low flying HDIs. It was found that the amplitude and frequency components of the dynamic microwaviness play an important role in slider dynamics. Furthermore, the effect of adhesive force on FHM was investigated and design guidelines for reduced FHM were suggested.This research was supported by a grant from the Information Storage Industry Consortium (INSIC) and the National Science Foundation under grant number CAREER CMS-0227842. Gary Prescott and Thomas Pitchford of Seagate Technology provided the spindle motor and HGA samples. The authors gratefully acknowledge this support.     

A probability method for prediction on High Cycle Fatigue of blades caused by aerodynamic loads

A probability method for prediction on High Cycle Fatigue (HCF) of blades caused by aerodynamic loads (PHBA) is erected and two approaches are adopted: improving the numerical method to obtain the dynamical responses of blades caused by aerodynamic loads and introducing probability theory into predicting HCF. The basic governing equations of fluid domain, solid domain and fluid–solid interface are given for flow-blade interaction system. Furthermore a numerical method named bidirectional sequential method is illuminated, and the corresponding physical process of vibration from unsteady state to steady state is described. The dynamical response can be obtained by this time domain method conveniently by the use of commercial softwares. Then PHBA is put forward based on vibration stress according to the probabilistic accumulative damage model. Finally an engineering sample is discussed to illuminate PHBA flow clearly. PHBA is performed on two types of second-stage stators to evaluate the operation security, thus the probabilistic accumulative damages altering with operation time are calculated, and the operational reliabilities are also obtained. The results can describe the possibility of HCF intuitively and quantitatively, which shows PHBA is very helpful in the HCF prediction and failure analysis.     

Design theory and vibration characteristics of a contact head slider

In this study, the design theory of a previously proposed contact head slider was extended by considering a thermally protruding head slider and the intermolecular adhesive force between the head and disk surfaces. The waviness-excited vibration characteristics of the thermally protruding contact head slider were analyzed using a single-degree-of-freedom slider model, whose contact stiffness was calculated in accordance with the Johnson–Kendall–Roberts adhesive contact theory. It was found that, because of the adhesive force, the resonance frequency f _r of the contact slider changed from zero to a value higher than the original second-pitch-mode resonance frequency with an increase in the head-penetration depth. Because the waviness-excited vibration of the contact slider is amplified at f _r , the first- and second-pitch-mode vibrations of the thermally protruding slider can be excited when f _r approaches those resonance frequencies. Because the friction force varies with the vibration of the contact slider, vibration modes of the slider-suspension system often observed at the beginning of contact can be explained. It is suggested that the region of the head-penetration depth for perfect contact sliding can be widened by increasing the effective contact damping and decreasing the disk waviness.     

Effect of reduction of slider pitch-mode vibration on magnetic-recording performance at low-clearance head–disk interface

Aiming at improvements of both stability of slider flying and magnetic-recording performance under a low-clearance condition, a “narrow-grooved slider” was constructed and demonstrated at drive level. The proposed slider has narrow grooves on its center pad of an air-bearing surface for attaining a high-damping effect on pitch-mode resonant vibration of the air bearing. The relationship between the high-damping effect and the pitch-mode resonant vibration was studied, and the magnetic-recording performance at the lube/slider interaction regime was improved. In this study, first, flying-height modulation (FHM) of the slider was analyzed in the frequency domain by using a fast Fourier transform. Compared with the narrow-grooved slider, a non-grooved slider showed a larger increase in high-frequency modulation of gap flying height when the clearance was reduced to near “zero” at which the slider is starting to interact with lube. Furthermore, by means of drive-level experiments, sector error rate (SER) as a function of flying clearance was investigated. Under a low gap flying height condition, HDDs with the non-grooved slider showed slight SER degradation during slider/lube interaction. However, the narrow-grooved slider did not show any SER degradation at the same gap flying height; the damping effect of the narrow-grooved slider suppressed high-frequency FHM, thereby preventing SER degradation in the slider/lube interaction region.     

Narrowband performance of active control on flow-induced vibrations inside hard disk drives

This paper presents an experimental study of narrowband active control on the flow-induced vibrations (FIV) on the head gimbals assembly (HGA) in a working hard disk drive (HDD). Firstly, experiments with an analog feedback close-loop were conducted as demonstration for narrowband active control on principal peaks in the spectrum of the off-plate FIV on the HGA whose signal was collected with a 1-D laser Doppler vibrometer (LDV). Secondly, the modal testing on the experimental HDD was carried out to find out where the spectrum principal peaks focused in current active control come from. Thirdly, a digital feedback control close-loop was implemented in experiments for narrowband suppression on the focused FIV spectrum peaks on the HGA. In those close-loops, the off-plate HGA vibrations detected by the LDV were used as feedback error signals, then the signals was passed through an analog or digital controller to generate feedback signals to drive a piezoelectric disk to actuate feedback acoustic pressure around the HGA. Active control experiments were conducted in narrow bands on five principal peaks in the HGA off-plate vibration spectrum, around 1,256, 1,428, 2,141, 2,519 and 3,469 Hz, respectively. It is shown that distinct narrowband suppression of at least 10 dB can be achieved on all these HGA vibration peaks.     

A parameter identification method for thermal flying-height control sliders

This paper employs higher order frequency response functions to describe the closed-form solution of nonlinear dynamics of MEMS thermal actuated flying-height control (TFC) slider, and employs the measured acoustic emission signal of a TFC slider during touch down as its vibration approximation to correlate with the derived closed-form solution for parameter identification. It is shown that during slider touchdown when heater power is increased gradually, the slider performs weak nonlinear vibrations in early transition phase, and exhibits linear vibration in the following steady sliding phase. These results are useful for the clarification of complicated dynamics and the designs of active sliders in sub-nanometer clearance regime.     

Direct Monte Carlo simulation of air bearing effects in heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is a promising high density recording technology in current hard disk industry. It is proposed to use a heat source from the slider system for heating up the recording media in order to increase its storage density. The heat generated from a heat spot on the disk and/or the higher slider body temperature in HAMR system could affect the slider air bearing and flying height. This paper studies the heat effects on slider air bearing characteristics by using the direct Monte Carlo simulation (DSMC) method. The simulation results show that the heat spot less than 50?nm in diameter could not affect much to the air bearing; however, its location should be away from the bearing pressure peak to minimize the heat spot effect. Furthermore, high temperature slider could increase the bearing pressure and force and the trend of force increment is independent of the flow channel length.     

Experimental study on slider dynamics during touchdown by using thermal flying-height control

To investigate the possibility of further lowering the clearance in head?Cdisk interface systems, slider dynamic behavior during a touchdown sequence with a thermal flying-height control (TFC) function was investigated by using a spinstand-level evaluation utilizing an acoustic emission (AE) sensor and a laser Doppler vibrometer (LDV). Experimental results demonstrated that off-track vibration was easier to excite by head?Cdisk contact at the beginning of head?Cdisk contact. We then confirmed that the amplitude of pitch-mode vibration in the flying-height direction increased and sway-mode vibration in the off-track direction decreased when increasing heater power during the touchdown sequence. Moreover, we found that the peak frequency of pitch-mode vibration shifted to a higher frequency under over-push conditions. Time?Cfrequency domain analysis results showed that the peak shift occurred at several locations during a disk rotation. The mechanism of the peak shift is attributed to the increase in stiffness at the head?Cdisk interface (HDI) due to solid?Csolid contact or mode change occurred in such regions. During the touchdown sequence, the friction force at the HDI continues to increase, even though slider vibration and AE signal decrease when heater power is increased. The friction force at the HDI needs to be decreased to achieve further low-clearance HDI.     

基于有限元模拟的薄膜热流计冲击振动分析

实现发动机热端部件热流的精准监测对于发动机的冷却设计和可靠性提高具有重要意义,而薄膜热流计具有结构简单、不影响被测件气动外形以及对流场干扰小等特点。针对航空发动机在运行时产生的高振动及高冲击载荷下的薄膜热流计结构可靠性问题,采用有限元方法,建立薄膜热流计的有限元模型,分析了冲击以及随机振动对热流计结构可靠性的影响,并且提出了优化建议。优化后的热流计的最大位移及最大应力都明显减少,结构的可靠性明显提升,冲击振动测试以及划痕测试的结果也验证了薄膜热流计结构的合理性。     

高速受电弓非定常气动特性分析

为保证高速列车受电弓与接触网之间具有良好的接触特性,针对强烈气流干扰会引起受电弓振荡的问题,用脱体涡模拟(Detached Eddy Simulation,DES)方法研究高速列车受电弓在开、闭口运行条件下的非定常抬升、阻力特性.结果表明,开、闭口运行对受电弓气动特性的影响有较大不同,尤其对受电弓及其滑板的抬升力波动影响明显.开口运行时整弓和滑板的抬升力波动幅度明显大于闭口运行;而开、闭口运行对整弓和滑板气动阻力的大小与波动幅度的影响很小。     

Simplified molecular gas film lubrication equation and accommodation coefficient effects

As the spacing between the flying head/slider and the rotating disk in hard disk drives (HDDs) continues to decrease, the interaction between the molecular gas and the surfaces of the disk and the head/slider becomes significant. The influence of surface accommodation coefficient (AC) is an important factor to govern the static characteristics of the head/slider. Starting from the polynomial logarithm fitting equations of Poisueille flow rate and Couette flow rate, a new simplified molecular gas film lubrication (MGL) equation is proposed to simulate the ultra-thin air bearing film in HDDs. The new MGL equation is simpler than that of the polynomial logarithm form of MGL equation. The new approach produces very good approximations for both Poisueille flow rate and Couette flow rate with very little differences to those based on the original MGL equation. The new simplified MGL equation is solved by using a meshless method, called least square finite difference (LSFD) method. Effects of ACs on the static characteristics of air bearing films in HDDs with ultra-low flying heights are investigated. Numerical results show that effects of ACs on the static characteristics are significant for the case of symmetric molecular interaction. On the other hand, effects of ACs at the disk surface on the static characteristics are significant for the case of non-symmetric molecular interaction, while effects of ACs at the slider surface on the static characteristics are weak.     

求解背包问题的贪心遗传算法及其应用

分析了文献[2]中求解背包问题(KP)的混合遗传算法(HGA)所采用的贪心变换方法缺陷;重新定义了贪心变换的概念,并给出了一种新的且更高效的贪心变换方法,将此方法与遗传算法相结合得到一种新的混合遗传算法,称之贪心遗传算法(简记GGA).利用GGA得出了文献[2,4]中一个著名KP问题实例的目前最好结果;同时,对于文献[7]中的KP问题实例和一个随机生成的KP问题实例,将GGA算法与求解KP问题的最有效算法HGA算法进行对比计算,结果表明GGA算法远远优于HGA算法.     

动车组司机室空调蒸发器气动噪声数值仿真

为研究动车组司机室空调蒸发器的噪声响应,建立某型司机室分体式空调蒸发器的计算流体动力学模型,采用FLUENT中的大涡模拟（large eddy simulation, LES）计算瞬态气动流场。对瞬态流场数据进行傅里叶变换,得到空气流场的频域数据。基于流场频域数据,采用Virtual.Lab的边界元法计算蒸发器的气动噪声,采用声压法计算蒸发器的辐射声功率,并与测试结果进行对比分析。结果表明：蒸发器出口位置气动噪声最高,最大声压级高于56 dB;最大声功率级出现在125~400 Hz的低频段;声功率级随着频率的增加逐渐降低,但在5 000 Hz的高频辐射中声功率级仍然超过55 dB,这表明空调蒸发器气动噪声属于宽频噪声;计算结果与测试结果吻合良好,验证声压法计算空调蒸发器气动声功率可行。     

Investigation of slider out-of-plane and in-plane vibrations during the track-seeking process

This paper employs the coupled air bearing model and modal order reduction (MOR) model of head stack assembly (HSA) to investigate the track-seeking process of a femto slider. Simulations indicate that the flying height and the pitch angle may increase or decrease significantly, depending on the track-seeking directions. For the slider studied in this paper, it is safer for sweeping from OD to ID, than sweeping from ID to OD. The most serious vibration is the off-track vibration, and it is highly related to the sweeping acceleration profile. A smooth acceleration profile is crucial to reduce all the vibrations of slider, especially the off-track vibration.