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Bias Force Compensation Method for Improved Settles in Direct Access Storage Device Actuator Systems

IP.com Disclosure Number: IPCOM000111173D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 103K

Publishing Venue

IBM

Related People

Erickson, KJ: AUTHOR [+4]

Abstract

Described is a method that can be used to improve the settling performance of high track density Direct Access Storage Device (DASD) files by compensating for the hysteresis effect in the position dependent bias force present in the actuator positioning system.

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Bias Force Compensation Method for Improved Settles in Direct Access
Storage Device Actuator Systems

      Described is a method that can be used to improve the settling
performance of high track density Direct Access Storage Device (DASD)
files by compensating for the hysteresis effect in the position
dependent bias force present in the actuator positioning system.

      The settling performance of an actuator control system
containing bias forces, such as those caused by an actuator flex
cable, can be improved by compensating for the bias forces, and
especially by compensating for the positional and directional
dependent hysteresis effects of these bias forces, as are often
observed in such systems.  This compensation involves the computation
of an integrator precharge value for the integrator portion of a PID
(Proportional, Integral, Derivative) controller such that the
integrator provides the necessary compensation to match the bias
force expected at the new seek location, thus providing for a
smoother settle response by reducing the dynamic effects caused by
error in the initial integrator value.

      A typical bias force curve exhibited in a DASD actuator system
is shown in the Figure.  This curve shows how the bias force changes
as the actuator is located to different positions between the inner
and outer diameters of actuator travel.  This curve also shows a seek
direction dependency that leads to a hysteresis effect in the shape
of the curve that is caused by a shift in the bias force for seeks
with move distances that substantially alter the position of the
actuator.

      The method used to compensate for the bias forces and their
hysteresis effects consists of measuring and taking the difference
between the bias force at the outer diameter track and the inner
diameter track, and dividing this difference by the number of tracks,
thus deriving the slope of the bias force curve.  The slope is used
in the equation to compute the...