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Title: High density magnetic recording
Keywords: fly-height, servo, control, HDD, PES, off-track
Issue Date: 2-Aug-2010
Citation: LIM JOO BOON MARCUS TRAVIS (2010-08-02). High density magnetic recording. ScholarBank@NUS Repository.
Abstract: The rapid growth in the areal densities of hard disk drives has posed challenges in the accurate positioning of the read/write head as the widths of the data tracks continue to narrow. To support high-density magnetic recording, the servo control system must be able to ensure the head stays on-track in the presence of various disturbances. In this thesis, the servo control mechanism of the Guzik spinstand was improved by implementing an actuation stage that incorporates a piezoelectric (PZT) actuator on the head cartridge to increase the overall bandwidth of the servo control system. This additional stage uses a Field Programmable Gate Array (FPGA) to demodulate the position error signal (PES) from the readback servo bursts and provide the control signal to the actuator driver to correct any off-track position. A frequency-encoded servo burst scheme is used to encode the position information on the disk and the firmware for the PES demodulation is based on a modified discrete Fourier Transform (DFT) algorithm. The system achieved a PES sampling rate of 15.36 kHz and was able to maintain accurate track-following in tests simulating 60 nm track-widths, with a very low non-repeatable position error of 1.76 nm. A significant portion of the areal density growth has been attributed to the reduction in the spacing between the head and disk, commonly known as the flying height, which increases the linear bit density. With the introduction of Thermal Flying Height Control (TFC) technology in recent years, flying heights under 10 nm have been achieved. TFC uses a miniature heater embedded in the slider to provide flying height control by varying the degree of downward protrusion of the slider pole tip through thermal expansion of the slider. However, besides a vertically downward protrusion, the thermal expansion from TFC also causes the head to shift its position in the lateral direction as the slider expands in every direction. This thesis also investigates the effect of the lateral shift in the position of the head during TFC to determine its impact on track-following and the possibility of track mis-registration during TFC.
Appears in Collections:Master's Theses (Open)

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