Hequn Min

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.

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.

Digital Feedback Control of the Flow-Induced Vibrations on the Head Gimbals Assembly in Hard Disk Drives: Design and Implementation

In this paper, a digital feedback control closed-loop is presented for active suppression of flow-induced vibrations on a head gimbals assembly (HGA) in a working hard disk drive (HDD). In this closed loop, a laser Doppler vibrometer was used to detect the flow-induced HGA off-plate vibration as feedback error signals, a digital controller was implemented to filter the feedback signals, and a piezoelectric disk stuck on the HDD cover inner surface was employed to actuate feedback acoustic pressure around the HGA to exert control on the HGA flow-induced vibrations. The digital controller was designed to enable the closed loop with capabilities of single or simultaneous multiple narrowband control on the HGA flow-induced vibrations. Experiments have been carried out for single- or multi-narrowband active suppression of five principal peaks in the HGA off-plate vibration spectrum, around 1256, 1432, 2144, 2524, and 3474 Hz, respectively. Results show that, with the digital closed loop, distinct vibration suppression of up to 15 dB was achieved on those single principal peaks in single-narrowband active controls, or simultaneous distinct suppression of up to 17 dB can be achieved on all those principal peaks in one multi-narrowband active control.

Narrowband Performance of Active Control on Flow-Induced Vibrations Inside Hard Disk Drives

This paper presents an experimental study of digital narrowband active control on the flow-induced vibrations (FIV) on the head gimbals assembly (HGA) in a working hard disk drive (HDD). Firstly, the modal testing on the HDD was carried out, in which the disk modes were analyzed with a 1-D laser Doppler vibrometer (LDV) and the HGA vibration modes with a 3-D LDV. Secondly, a digital feedback control close-loop was implemented in experiments to suppress the FIV spectrum peaks on the HGA. In this close-loop, the HGA vibrations detected by the LDV were used as feedback error signals, then the signals was passed through a 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 1256Hz, 1428Hz, 2141Hz, 2519Hz and 3469Hz, respectively. It is shown that distinct suppression of at least 10 dB can be achieved on all these HGA vibration peaks.Copyright

Feedback Control of Flow-Induced Vibrations on Head Gimbals Assembly Inside Hard Disk Drives

High speed flows in working hard disk drives (HDDs) can induce off-track vibrations on a head gimbals assembly (HGA), which limit positioning accuracy of the slider magnetic head on the tip of the HGA for high magnetic storage density in disks. This paper presents experimental studies and numerical simulations on the flow-induced vibrations (FIV) of the HGA inside an HDD and active control of such vibrations. First, the HGA off-track vibration and the airflow pressure fluctuations around the HGA are measured to characterise the FIV of the HGA. Second, we propose an active control strategy for such FIV of the HGA, in which feedback acoustic pressures are employed to suppress pressure fluctuations in turbulence around the HGA. Numerical simulations have been carried out on this issue by introducing virtual sensors into the close regions around the HGA. Finally, by using the FIV on the HGA as feedback error signals through the laser Doppler vibrometer, the feedback control of FIV on the HGA has also been demonstrated.

Virtual sensing in local active suppression on pressure fluctuations for controlling flow-induced vibration in hard disk drives

Numerical simulations are presented on a feedback active control strategy for flow-induced off-track vibration of the head gimbals assembly (HGA) supporting the slider in hard disk drives, through suppressing pressure fluctuations around the HGA. A virtual sensing method is employed to enable the feedback signal changeable from pressure fluctuations at the physical sensor position to those at single “virtual sensor” positions closely around the HGA or a spatial average of pressure fluctuations along an HGA surface. Based on a linear control methodology, performance of the proposed active control strategy with different feedback signals has been investigated in two-dimensional simulations, where a physical pressure sensor and a pressure actuator are assumed on the inner-surface of the HDD cover to detect the pressure fluctuations and to actuate active pressure oscillations into HDD space respectively. The results show effective control on the HGA off-track vibration when the feedback signal is configured to minimize pressure fluctuations at specific positions closely around the HGA, such as the wake region. It is also shown that satisfying control effect can be achieved on the HGA off-track vibration in the global spectrum when the feedback signal is configured to minimize the spatial average of pressure fluctuations along the upper surface of the HGA.Copyright