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MAXIMUM SEEK VELOCITY ADJUSTMENT BY TORQUE FACTOR PROFILE

IP.com Disclosure Number: IPCOM000014591D
Original Publication Date: 1999-Dec-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

LJ SERRANO: AUTHOR [+2]

Abstract

Disk drive servo systems are designed to work over a range of operating environments and manufacturing variations; accomplishing this requires a sacrifice to performance in the nominal environment with the nominal plant. Specifically, as the temperature of the VCM increases, the coil resistance increases and consequently the maximum acceleration of the actuator decreases. And the coil resistance itself may vary from drive to drive due to manufacturing variations; this, too, will alter the maximum acceleration. Further, the power supply is allowed to fluctuate within a few percent of nominal and when the voltage supply is lower than nominal, the maximum acceleration is also lower than nominal. These factors may individually or in sum result in a limit to the control that is significantly lower than nominal. To prevent seek failures, the velocity profile must be designed with this control limitation in mind; this in turn reduces the maximum performance when these factors and thus the control limit are nearly nominal.

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MAXIMUM SEEK VELOCITY ADJUSTMENT BY TORQUE FACTOR PROFILE

Disk drive servo systems are designed to work over a range of operating
environments and manufacturing variations; accomplishing this requires a
sacrifice to performance in the nominal environment with the nominal plant.
Specifically, as the temperature of the VCM increases, the coil resistance
increases and consequently the maximum acceleration of the actuator decreases.
And the coil resistance itself may vary from drive to drive due to
manufacturing variations; this, too, will alter the maximum acceleration.
Further, the power supply is allowed to fluctuate within a few percent of
nominal and when the voltage supply is lower than nominal, the maximum
acceleration is also lower than nominal. These factors may individually or in
sum result in a limit to the control that is significantly lower than nominal.
To prevent seek failures, the velocity profile must be designed with this
control limitation in mind; this in turn reduces the maximum performance when
these factors and thus the control limit are nearly nominal.

   The novel advance is that this invention
degrades performance only in proportion to the
limitation on the maximum control.

   The solution takes three steps. First, measure
the maximum acceleration of the drive by performing
a set of seeks using maximum available control.

The outcome of these seeks is a predicted distance
traveled and an actual distance traveled. Second,
determine from the results of these calibrating
seeks the ratio of the actual maximum acceleration
to the nominal maximum acceleration: this ratio is
equal to the ratio of the actual distance traveled
to the predicted distance traveled, and it provides
a great deal of information on the state of the
disk drive. Specifically, if the ratio is low,
then the maximum acceleration is low, and hence the
control is more constrained than nominal. This
means that either the coil resistance is high, or
the power supply voltage is low, or both. The
third step is to take corrective action when the
control is too constrained. This action...