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Method to Synchronize Direct Access Storage Device Spindles Using Off-the-Shelf Hardware And Digital Control Techniques

IP.com Disclosure Number: IPCOM000101927D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 128K

Publishing Venue

IBM

Related People

Erickson, KJ: AUTHOR [+2]

Abstract

A method is described that can be used to synchronize direct access storage device (DASD) spindles of a type that use a fixed frequency source as a means to set the spindle speed. This method is essentially an "add-on" circuit that takes control of the fixed frequency source such that the spindle speed can be varied over a small range from nominal. A distinguishing feature of this method is that it allows many of the available "off-the-shelf" brushless DC motor control modules to be used "as is", i.e., as they would be for normal fixed spindle speed/ non-synchronized applications.

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Method to Synchronize Direct Access Storage Device Spindles Using Off-the-Shelf Hardware And Digital Control Techniques

       A method is described that can be used to synchronize
direct access storage device (DASD) spindles of a type that use a
fixed frequency source as a means to set the spindle speed. This
method is essentially an "add-on" circuit that takes control of the
fixed frequency source such that the spindle speed can be varied over
a small range from nominal.  A distinguishing feature of this method
is that it allows many of the available "off-the-shelf" brushless DC
motor control modules to be used "as is", i.e., as they would be for
normal fixed spindle speed/ non-synchronized applications.

      The spindle speed of most brushless DC motors used in DASD
files is determined by the frequency of the oscillator input to the
motor driver module.  The motor driver controls the spindle speed by
regulating the motor drive based on the error generated by a speed
discriminator which detects the number of oscillator pulses that
occur in a certain portion of a spindle revolution.  If the
oscillator input changes, then the spindle speed will change to
cancel the speed discriminator error.  See Fig. 1 for a block diagram
of the basic spindle speed control loop.

      A second control loop can be constructed around the motor
driver such that the speed of the spindle can be adjusted to
synchronize a once-per-revolution index signal to an external
synchronizing pulse.  A "position" error between the index signal and
the synchronizing pulse is the input to this control loop, which is
used to generate an output that can adjust the spindle speed by
changing the frequency of the oscillator input to the motor driver.

      This control loop utilizes a tri-frequency motor oscillator
circuit, a sample interrupt generator, and a microcontroller, which
includes two integrated multi-purpose programmable timers.  See Fig.
2 for a block diagram of the modified spindle speed control loop for
synchronization.

      The tri-frequency oscillator generates three frequencies that
are used to control both the spindle speed and the "position" of the
index signal with respect to the synchronizing pulse.  The three
frequencies generated are the nominal frequency, and the high and low
frequencies. The nominal frequency is the same frequency that would
be used to determine the motor speed in a non-synchronizing
application.  It is also the default frequency selected if there is a
loss of either the index signal or the synchronizing pulse.  The high
and low frequencies typically vary from the nominal frequency by less
than one percent. These frequencies are used to speed up or slow down
the motor in order to "seek" the index signal to the synchronizing
pulse such that the two signals are synchronized in time.  In order
to servo the index...