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Multilevel Tuned Torque Amplification Routine

IP.com Disclosure Number: IPCOM000101402D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 4 page(s) / 123K

Publishing Venue

IBM

Related People

Plutowski, EF: AUTHOR

Abstract

Torque amplification is a means of getting more starting torque from a motor than it can normally provide. This is done by sinusoidally oscillating a DC brushless spindle motor in a hard disk storage file. In this process the output torque of the spindle motor increases with each oscillation cycle.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Multilevel Tuned Torque Amplification Routine

       Torque amplification is a means of getting more starting
torque from a motor than it can normally provide.  This is done by
sinusoidally oscillating a DC brushless spindle motor in a hard disk
storage file.  In this process the output torque of the spindle motor
increases with each oscillation cycle.

      Stiction is a problem in hard disk storage files where the head
sticks to the disk.  The stiction is due to having the smooth head in
contact with a smooth disk.  The stiction force is worse with the
presence of disk lube or disk contaminants which increase the
cohesive force between the two smooth surfaces of the disk and head.
As the number of head/disk interfaces increases, this problem gets
worse.  A typical rigid disk file may have 16 head/disk interfaces.
Due to the number of head/disk-interface combinations that can have
stuck heads, it was not feasible to have a fixed one part torque
amplification algorithm that would work properly.

      Torque amplification is a means by which a spindle motor is
oscillated at a resonant frequency which is dependent on the number
of heads stuck to the disk of a hard disk storage file.  By
oscillating the motor, the force of the head stuck to the disk can be
overcome to release the head and spin the motor up to speed.  The
problem that arises is that with a varying number of heads stuck, the
stiction force and spring constant of the system due to the head
suspension varies widely.  This then changes the resonant frequency
of the system to obtain the proper torque required to release the
head from the disk.

      As an example, if the motor is oscillated at a resonant
frequency due to 14 heads stuck and only 8 heads are stuck, then due
to the improper oscillation frequency, the torque will not increase
with each cycle.  The oscillations will have a destructive
interference effect on each other.  To overcome this problem, the
torque amplification routine is composed of several stages, each
stage tuned to a number of stuck heads.  A proposed algorithm has
three stages, though this could be in as many stages as needed to
tune each part to a certain number of stuck heads.  Stage one is
tuned to release zero to eight stuck heads, (this is the normal start
stage), stage two releases twelve to sixteen heads, and stage three
releases from eight to twelve stuck heads.

      A DSL module was used that allowed the following variables to
be altered.  Following the variable is a description of its effect on
the overall system response.
Damping factor:  This effect is due to head/disk friction of loose
heads.  This value was not precisely known. In the model an assumed
value was used and output torque results were compared relative to
each other.
Duty Cycle:      This is the per...