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Optimum Access Time for Track-To-Track Movement

IP.com Disclosure Number: IPCOM000101673D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 4 page(s) / 128K

Publishing Venue

IBM

Related People

Pham, IV: AUTHOR

Abstract

The closed-loop feed forward algorithm can be used to improve track-to-track access time.

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Optimum Access Time for Track-To-Track Movement

       The closed-loop feed forward algorithm can be used to
improve track-to-track access time.

      Digital servo uses velocity trajectory to generate command
during seeking.  Its input is distance from the target and its output
is the velocity command.  As would be expected, this velocity command
is high as the actuator is far from the target and approaches zero as
it gets closer to the desired track location.  In the first half of
the seek, trajectory output is mainly used to get the actuator
moving. In the second half, it is a desired velocity and is used to
guide the actuator to the target cylinder.  The disadvantage of this
design is that it does not run closed loop in the first half, so it
is sensitive to the plant parameters and initial conditions.

      Fig. 1 compares the new trajectory with the prior art. The new
trajectory provides the desired velocity for an entire seek.  It
reassembles the time optimum actuator velocity.  It starts at rest,
peaks in the middle of the seek and ends at rest.  The new algorithm
uses the feed forward signal to provide initial actuator
acceleration. Fig. 1 also shows another advantage of the new
algorithm.  In the second half of the seek, the desired velocity for
the new trajectory is much higher than the prior art one.  The new
trajectory converges to the linear optimal position feedback gain at
about 0.6 track away from the target.  This is compared to 0.08 track
for the prior-art design.  With the optimal gain, servo will come to
the target quicker, and will also recover from the disturbance
quicker than the prior-art design.

      The basic servo architecture is similar to the prior art except...