eprintid: 236
rev_number: 16
eprint_status: archive
userid: 7
dir: disk0/00/00/02/36
datestamp: 2009-08-26 16:21:53
lastmod: 2015-05-29 19:50:42
status_changed: 2009-08-26 16:21:53
type: report
metadata_visibility: show
item_issues_count: 0
creators_name: Maki, Kara
creators_name: Ozlem, Melih
creators_name: Schwendeman, Don
creators_name: Please, Colin
creators_name: Phillips, Joel
creators_name: Case, Michael
creators_name: Heryudono, Alfa
creators_name: Bhalezcio, Kishor
creators_name: Atena, Agegnehu
creators_name: Witelski, Tom
creators_name: Sun, Jiguang
creators_name: Fehribach, Joseph
corp_creators: Ferdinand Hendriks
title: Maximizing Minimum Pressure in Fluid Dynamic Bearings of Hard Disk Drives
ispublished: pub
subjects: telecom
studygroups: mpi23
companyname: Hitachi GST
full_text_status: public
abstract: We focus on the central spindle which supports the rotating magnetic platters which hold all of the data. The spindle must operate with great precision and stability at high rotational speeds. Design practice has converged on oil-lubricated hydrodynamic journal bearings as the most common choice for spindles. That is, a layer of viscous oil separates a rotating shaft (the bearing) from the fixed outer sleeve (the journal). In hard drives, it is very important for the shaft to be centered within the sleeve. Plain journal bearings (i.e. both surfaces are circular cylinders) are unstable to perturbations that push the shaft off-center. It was found that this stability problem can be overcome by cutting diagonal grooves into the journal in a pattern called a herring-bone. Another consequence of this design is that very high pressures are generated by the grooves as they drive the oil to the middle of the bearing, away from the top/bottom ends of the spindle. This pumping action generally works to oppose leakage out of the bearing.

We examine how choices for the groove pattern can influence the key properties of the bearing. The focus is to understand the effect of the groove geometry on the pumping action. In particular the undesirable behavior caused by the low pressures created near the top/bottom ends of the bearing which, under many conditions, may result in the pressure becoming negative, relative to atmospheric pressure. Negative pressure can result in cavitation or, when it occurs near an air-oil interface, can cause air to be ingested and hence create bubbles. Any bubbles in the oil can corrupt the lubricating layer in the bearing and, as they are created and collapse, can cause significant undesirable vibrations. The negative pressures have therefore been identified as one of the key problems in design of hard disk drive bearings.

We will use numerical computations and some analysis to show that by modifying the groove geometry we can reduce the negative pressure while retaining good stability characteristics.
date: 2007
citation:   Maki, Kara and Ozlem, Melih and Schwendeman, Don and Please, Colin and Phillips, Joel and Case, Michael and Heryudono, Alfa and Bhalezcio, Kishor and Atena, Agegnehu and Witelski, Tom and Sun, Jiguang and Fehribach, Joseph  (2007) Maximizing Minimum Pressure in Fluid Dynamic Bearings of Hard Disk Drives.  [Study Group Report]     
document_url: http://miis.maths.ox.ac.uk/miis/236/1/Hitachi_final.pdf