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Shock-Resistant Rotary Microactuator for Fine Positioning of Recording Heads

IP.com Disclosure Number: IPCOM000113418D
Original Publication Date: 1994-Aug-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 224K

Publishing Venue

IBM

Related People

Fan, L-S: AUTHOR [+3]

Abstract

A primary trend in magnetic disk drives is that the magnetic bit size, which may be reliably written and read, continues to decrease at a rate around 60% per year (or even higher). One obvious consequence is that the width of the track which contains the sequential bits must also diminish at roughly half this rate. Thus, an advanced storage device having 4000 to 5000 tracks per inch (tpi) today is likely to have 20 to 25 ktpi by the year 2000. This is projected to place extreme requirements on the precision with which the actuator system brings the recording head to the data track and maintains the head over the track. Furthermore, the range of applications for which disk drives are being used has changed from one in which stable, relatively massive units are protected from substantial operating shocks.

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Shock-Resistant Rotary Microactuator for Fine Positioning of Recording
Heads

      A primary trend in magnetic disk drives is that the magnetic
bit size, which may be reliably written and read, continues to
decrease at a rate around 60% per year (or even higher).  One obvious
consequence is that the width of the track which contains the
sequential bits must also diminish at roughly half this rate.  Thus,
an advanced storage device having 4000 to 5000 tracks per inch (tpi)
today is likely to have 20 to 25 ktpi by the year 2000.  This is
projected to place extreme requirements on the precision with which
the actuator system brings the recording head to the data track and
maintains the head over the track.  Furthermore, the range of
applications for which disk drives are being used has changed from
one in which stable, relatively massive units are protected from
substantial operating shocks.  High-density magnetic storage is now
being found in portable or other lightweight applications, such as
laptop or notebook computers, which allow the drive to be exposed to
greater vibrations and shock in any orientation.  Since the allowable
offset between the actual head position and the track center, called
the track misregistration (TMR), is a fixed amount related to the
width of the track (approximately 12% of the track-to-track pitch),
this increased level of vibrations becomes even more troublesome for
future decreased track dimensions.

      One area in particular will require further advancement to
accommodate this increased need for tracking precision.  This is the
speed or servo bandwidth with which the head positioning servo system
can respond.  Currently, the servo bandwidth is approximately 500 to
600 Hz for many drive systems, but as we extend the track pitch to
smaller dimensions, this must be increased.  One approach which may
allow such an increase in bandwidth, and which may be the necessary
solution to the problem, is the use of a second actuator (a
microactuator) to provide rapid, small-motion, position correction of
the recording head.  This concept of a two-stage, coarse/fine servo
system has been proposed and described elsewhere (1-3) for linear
motion of the recording element using electrostatic, electromagnetic,
or piezoelectric activation.  Discussed here is a variation of the
concept in which an electrostatic rotary microactuator is used for
fine adjustment of the position of the recording element.  One added
advantage of this approach is the inherent shock resistance of a
rotary device to most shock events.

      The field of micromechanics and related processing techniques
is an area of technology which has undergone rapid growth in
capabilities and applications.  Microactuators are examples of small
mechanical devices which may be fabricated using many of the
lithographic techniques and materials developed for the semiconductor
industry (4-6).  Small plated devices have been proposed for
recording...