2,983 research outputs found
Heat transfer across a nanoscale pressurized air gap and its application in magnetic recording
In this study, we investigated how a thermally actuated air bearing slider heats up a fast-spinning storage disk through a highly pressurized nanoscale air gap in a magnetic recording system. A Euleriandescription- based computational approach is developed considering heat conduction through a pressurized air film and near-field radiation across the gap. A set of field equations that govern the air bearing dynamics, slider thermo-mechanics and disk heat dissipation are solved simultaneously through an iterative approach. A temperature field on the same order as the hot slider surface itself is found to be established in the disk. The effective local heat transfer coefficient is found to vary substantially with disk materials and linear speeds. This approach quantifies the magnitude of different thermal transport schemes and the accuracy is verified by an excellent agreement with our experiment, which measures the local slider temperature rise with a resistance temperature sensor. It also demonstrates an effective computational approach to treat transient thermal processes in a system of components with fast relative speed and different length scales. Finally, the investigated thermal transport mechanism leads to a substantial spacing change that has a significant impact on the spacing margin of today’s magnetic storage systems
REAL-TIME SIGNAL PROCESSING FOR FLYING HEIGHT MEASUREMENT AND CONTROL IN HARD DRIVES SUBJECT TO SHOCK AND VIBRATION
Merged with duplicate record 10026.1/829 on 10.04.2017 by CS (TIS)Three readback signal detection methods are investigated for real-time flying height or
head disk spacing variation measurement under vibration conditions. This is carried out
by theoretical analysis, numerical simulation, and experimental study. The first method
(amplitude detection) provides a simple way to study the head disk spacing change. The
second method ( PW50 parameter estimation) can be used effectively for real-time
spacing variation measurement in normally operated hard disk drives, primarily in low
frequency spacing variation conditions. The third method (thermal signal detection), on
the other hand, is more effective and suitable for high frequency spacing variation
measurement. By combining the PW50 estimation and thermal signal detection
methods, a noval spacing variation detection method for the whole frequency range is
constructed. This combined signal detection method not only has been used to study the
head disk spacing variation itself, but also has the potential of being used for real time
flying height control.
Analytical models are developed for head disk assembly and head position servo control
mechanisms to analyse the operation failure of hard disk drives under vibration
conditions. Theoretical analysis and numerical simulation show their good agreement
with experimental results.
A novel active flying height control method is proposed to suppress the flying height or
head-disk spacing variation in hard disk drives under vibration conditions. Simulation
results show that this active flying height control can effectively suppress the head-disk
spacing variation, therefore the performance and reliability of HDDs can be well
improved when working in vibration conditions: The method has a good potential to be
applied to future ruggedized hard disk drives
Dynamic Characterisation of the Head-Media Interface in Hard Disk Drives using Novel Sensor Systems
Hard disk drives function perfectly satisfactorily when used in a stable
environment, but in certain applications they are subjected to shock and vibration.
During the work reported in this thesis it has been found that when typical hard disk
drives are subjected lo vibration, data transfer failure is found to be significant at
frequencies between 440Hz and 700Hz, at an extreme, failing at only Ig of sinusoidal
vibration. These failures can largely be attributed to two key components: the
suspension arm and the hard disk. At non-critical frequencies of vibration the typical
hard disk drive can reliably transfer data whilst subjected to as much as 45g.
When transferring data to the drive controller, the drive's operations are
controlled and monitored using BIOS commands. Examining the embedded error
signals proved that the drive predominantly failed due lo tracking errors.
Novel piezo-electric sensors have been developed to measure unobtrusively
suspension arm and disk motion, the results from which show the disk to be the most
significant failure mechanism, with its First mode of resonance at around 440Hz. The
suspension arm movement has been found to be greatest at IkHz.
Extensive modelling of the flexure of the disk, clamped and unclamped, has
been undertaken using finite element analysis. The theoretical modelling strongly
reinforces the empirical results presented in this thesis.
If suspension arm movement is not directly coupled with disk movement then
a flying height variation is created. This, together with tracking variations, leads to
data transfer corruption. This has been found to occur at IkHz and 2kHz.
An optical system has been developed and characterised for a novel and
inexpensive flying height measurement system using compact disc player technology
DEVELOPMENT OF IMPROVED HEAD-DISK SPACING MEASUREMENT METHODS FOR MAGNETIC DISK DRIVES
A detailed review of existing flying height or head disk spacing testing techniques has
been made, and in-depth analyses of the working principles of the currently popular
optical interferometry flying height testing methods are presented with simulation
results. A new dual-beam normal incidence polarisation inteferometry method is then
proposed. One advantage of this dual-beam polarisation interferometry is that it can be
used for both the direct spacing measurement (DSM) method and relative displacement
measuring (RDM) method. The RDM method is a good way to measure the head-disk
spacing and the slider pitch or roll when a real magnetic disk is used for testing. The
DSM method has the advantage that the absolute head-disk spacing can be observed and
measured directly, especially in the case where it is difficult for the light beam to 'spot'
the back surface of the head-slider. When used for the DSM method, the flying height
can be measured down to contact without losing sensitivity. Slider pitch or roll can also
be measured using the phase information. Another advantage of this polarisation
interferometry is that, when used for the DSM method, with the measured intensity and
phase information, the optical constants of the slider material can be determined, which
is necessary to determine the flying height. By investigation of the application limits
and potential problems of the intensity interferometry method, an improved intensity
interferometry method is also proposed by using phase-shifting technique to improve
the sensitivity of this method when the head-disk spacing is below 10 nm and near
contact. An experimental testing system has been built to test the capability and
effectiveness of the proposed interferometry methods. Experimental results are
presented which show good agreement with the results gained from theoretical analyses
and simulation
THE DEVELOPMENT OF A NOVEL SUSPENSION ARM WITH 2-DIMENSIONAL ACTUATION, FOR USE IN ADVANCED HARD DISK DRIVES
As magnetic computer disks are developed to ever-greater data storage densities, the accuracy
required for head positioning is moving beyond the accuracy provided by present technology using
single-stage voice-coil motors in hard disk drives. This thesis details work to develop a novel active
suspension arm with 2-dimensional actuation for use in advanced hard disk drives. The arm
developed is capable of high-bandwidth data tracking as well as precision head flying height control
motion. High-bandwidth data tracking is facilitated by the use of piezoelectric stack actuator,
positioned closer to the head.
The suspension arm is also capable of motion in the orthogonal axis. This motion represents active
flying height control to maintain the correct altitude during drive operation. To characterise the
suspension arm's structural dynamics, a high-resolution measurement system based on the optical
beam deflection technique has been developed. This has enabled the accurate measurement of
minute end-deflections of the suspension arm in 2-dimensions, to sub-nanometre resolution above
noise. The design process of the suspension arm has led into the development of novel
piezoelectric-actuated arms. In the work involving lead zirconate titanate (PZT) thick films as
actuators, work in this thesis shows that reinforcing the films with fibre improves the overall
actuation characteristics of the thick films. This discovery benefits applications such as structural
health monitoring.
The final suspension arm design has been adopted because it is simple in design, easier to integrate
within current hard disk drive environment and easier to fabricate in mass. Closed-loop control
algorithms based on proportional, integral and derivative (PID) controller techniques have been
developed and implemented to demonstrate high bandwidths that have been achieved. The
suspension arm developed presents an important solution in head-positioning technology in that it
offers much higher bandwidths for data tracking and flying height control; both very essential in
achieving even higher data storage densities on magnetic disks at much reduced head flying heights,
compared to those in existing hard disk drives
Three-Dimensional Direct Simulation Monte Carlo Method for Slider Air Bearings
The direct simulation Monte Carlo (DSMC) method is used to solve the three-dimensional nano-scale gas film lubrication problem between a gas bearing slider and a rotating disk, and this solution is compared to the numerical solution of the compressible Reynolds equations with the slip flow correction based on the linearized Boltzmann equation as presented by Fukui and Kaneko [molecular gas film lubrication (MGL) method] [ASME J. Tribol. 110, 253 (1988)]. In the DSMC method, hundreds of thousands of simulated particles are used and their three velocity components and three spatial coordinates are calculated and recorded by using a hard-sphere collision model. Two-dimensional pressure profiles are obtained across the film thickness direction. The results obtained from the two methods agree well with each other for Knudsen numbers as large as 35 which corresponds to a minimum spacing of 2 nm. The result for contact slider is also obtained by the DSMC simulation and presented in this paper
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