Qide Zhang

Aerodynamic Pressure Fluctuations Associated With Flow-Induced Vibration of the Head Gimbals Assembly Inside a Hard Disk Drive

This paper presents an experimental investigation and numerical simulation on the spectrum-spatial characteristics of aerodynamic pressure fluctuations around the head gimbals assembly (HGA) in a working hard disk drive (HDD). The pressure fluctuations are measured through tiny holes on the HDD top cover above the HGA. The positioning error signal and servo system sensitivity in the working HDD are measured as well to evaluate the slider off-track vibration. Comparisons between the spectra of pressure fluctuations and the slider off-track vibration show that, the pressure fluctuations around the HGA are highly associated with the slider off-track vibration in terms of principal peaks in the spectra, especially at 1.83 kHz and 2.54 kHz. The results also show that the spatial coherence of pressure fluctuation around the HGA remains high at frequencies around the principal peaks in the spectra, which has been further confirmed by the numerical simulation based on a two-dimensional large eddy simulation model. It is concluded that the flow-induced HGA vibrations in an HDD can be detected and evaluated through the pressure fluctuations by a sensor around the HGA.

Active Control of Flow-Induced Vibrations on Slider in Hard Disk Drives by Suppressing Pressure Fluctuations With Virtual Sensing

This paper presents numerical simulations on a feedback active control strategy for flow-induced off-track vibration of a head gimbals assembly (HGA) bearing a slider in hard disk drives (HDDs). In the proposed active control strategy, a physical pressure sensor is assumed on the HDD cover to detect the pressure fluctuations and a pressure actuator is on the inner surface of the HDD cover to actuate feedback acoustic pressures to suppress pressure fluctuations in airflow turbulence around the HGA. A virtual sensing method is employed to enable the system feedback signal changeable from the physical pressure sensor to specific “virtual pressure sensors” closely around the HGA. The performance of the proposed active control strategy has been numerically examined based on a turbulence model of a 2-D channel flow with large eddy simulation. The results show that successful active control on the HGA off-track vibration can be achieved if the feedback signal is configured by virtual sensing to minimize the pressure fluctuations at specific positions closely around the HGA. It is also shown that the wake zone of the HGA is a typical virtual sensing position for pressure fluctuations in the feedback control system in order to achieve suppression on the HGA off-track vibration.

Active Control of Flow-Induced Vibrations on Slider in Hard Disk Drives: Experimental Demonstration

This paper presents an experimental demonstration on the active control of flow-induced vibrations on a head gimbals assembly (HGA) bearing a slider in a hard disk drive (HDD). The feedback control closed-loop consisted of a laser Doppler vibrometer (LDV), a narrowband frequency filter, a signal conditioner, an in-house made phase shifter, and a piezoelectric disk mounted on the inner surface of the HDD cover. The HGA vibrations detected by the LDV were used as feedback error signals, and the signals were then phase shifted and amplified to drive the piezoelectric disk to generate feedback acoustic pressure around the HGA. The phase shift and gain of the feedback loop were adjusted such that the HGA vibrations were reduced. The experiments of active control have been conducted on five principal peaks in the HGA off-plate vibration spectrum, around 1256, 1428, 2141, 2519, and 3469 Hz, respectively. The results show that reduction of the HGA vibrations can be achieved on all these principal peaks, with a maximum suppression of 16 dB on the peak around 1428 Hz. It is also observed that simultaneous reduction can take place among these peaks when the narrowband feedback control is focused only on one of them.

A numerical simulation of particle trajectory in thin hard disk drive

This work numerically investigates the particle trajectory in a turbulent flow field and its trapped status in 2.5 inch thin hard disk drives (HDDs). The trajectory of particle is calculated and the particle trapped status is studied by statistical analysis of the behavior of massive particles. Two air filter designs are compared and evaluated. The effects of particle release position, particle size and density on the trapped status are examined. The results indicate that the filter should be arranged far from the read/write head, and the particle trapped status depends on the particle size and particle release position. The simulation results provide useful information and can be used as a guideline in the design of particle removal system inside thin HDDs.

A new fluid structure coupling approach for high frequency/small deformation engineering application

The present work introduces an engineering approach to investigate the coupled fluid-structure interactions for high-frequency and small displacement problems. A new sequential coupling method is developed to investigate the fluid-structure interactions in high-frequency and small displacement systems. The new method is based on the idea that the structure immersed in the fluid vibrates due to the flow force, and in turn the vibrating structure also imposes a reaction power to the surrounding flow. The reaction power is interpreted by a boundary vibrating velocity. The new developed fluid-structure coupling approach is applied to a model disk drive and the results indicate that the dominant coupling effect is induced by the first frequency boundary vibration in out-of-plane direction. Without consideration of coupling effects, the arm vibration amplitude is overestimated in the out-of-plane direction, and underestimated in the in-plane direction. The turbulent flow behavior and the characteristics around vibrating boundary are revealed under the influence of the coupling approach. The simulation results are examined and verified by LDV measurements, which confirm that the newly developed approach is feasible for predicting the vibration amplitude of immersed vibration boundaries.

Active Control on Flow-Induced Vibration of the Head Gimbals Assembly in Hard Disk Drives

A feedback active method is proposed to control the flow-induced vibration (FIV) of the head gimbals assembly (HGA) through suppressing the pressure fluctuations around the HGA. Firstly pressure fluctuations and FIV measurements are carried out around the HGA in a working hard disk drive, and the results show a high correlationship between the spectra of the HGAs FIV and the pressure fluctuations. Secondly numerical simulations are conducted to investigate the control effect on the HGAs FIV by the proposed feedback active method with a pressure virtual sensing architecture. The numerical results show that the HGAs FIV can be successfully controlled through suppressing the pressure fluctuations with virtually sensing pressure in the wake zone of the HGA.

An Experimental Study on Vibration of Disks Mounted on Hard Disk Drive Spindles

Disk vibration is a major problem that causes track misregistration. In this work, the vibration characteristics of 3.5 inch disks and 2.5 inch disks mounted on ball bearing and fluid bearing spindles were experimentally investigated and compared. The differences between disks mounted on these two types of spindles are then presented and analyzed. It was found that the most significant difference was that no rocking mode was observed for disks supported by fluid bearing spindle motors.

Analysis of hydrodynamic journal bearing with GDQ method

Generalised Differential Quadrature (GDQ) method is a high-order numerical method. It uses the information on all grid points to approach the derivatives of the unknown function. With GDQ method, it is possible for us to obtain the same accurate results but use less grid points and less computing time than that of FDM/FEM. The present work reports the results of analysing journal bearing with GDQ method. The results are compared with those obtained by FDM/FEM and good agreement between these results is observed.

Numerical investigation of thermal problems in HAMR system

The paper numerically investigated two thermal related problems in heat assisted magnetic recording: the dependence of the recorded mark width on the laser power and the temperature distribution and changes with time in lubricant layer at the condition without or with the heat sink layer. The results show that the mark width increases as the laser power increases and heat sink layer helps to reduce temperature in lubricant layer.

Flow-induced vibration in Hard Disk Drives

The paper introduces and discusses the impact of flow induced vibrations on the performance of Hard Disk Drives (HDD). Two major flow structure interactions of HDDs, flow-induced disk flutter and flow-induced vibration of head gimbal assembly, are discussed. Methods of visualising, measuring and predicting flow field in HDDs are first introduced. Subsequently, methodologies are discussed aiming at measuring disk flutter, calculating the effects of disk flutter on track mis-registration and reducing the effects of disk flutter. Lastly, future research topics on airflow in HDDs are discussed.