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# Linear Control Algorithm for Direct-Access Storage Devices

IP.com Disclosure Number: IPCOM000100921D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 91K

IBM

## Related People

Bailey, B: AUTHOR [+3]

## Abstract

Disclosed is a method of controlling the spindle motor speed for direct-access storage devices (DASDs) using a linear control algorithm.

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

Linear Control Algorithm for Direct-Access Storage Devices

Disclosed is a method of controlling the spindle motor
speed for direct-access storage devices (DASDs) using a linear
control algorithm.

The linear control algorithm controls the spindle motor speed
to within a very close tolerance of nominal speed by varying the
current supplied to the motor to account for changes in the load due
to windage and actuator position. Changes in the windage forces
inside the head-disk assembly (HDA) can cause the load on the spindle
motor to change. Windage forces can be affected by actuator position.
Therefore, since the actuators can move quickly to various positions
in the HDA, the linear control algorithm must have a fast response
time to the changes in windage forces in order to control the motor
speed accurately.

A microcontroller is used to control and monitor the spindle
motor speed.  The microcontroller commutates the motor by writing a
pattern to the spindle motor drivers.  It also determines the speed
of the motor by measuring the time for one revolution using a
hardware time.  It then uses the measured time to calculate a new
motor current value, and output it to a latch which feeds the
digital-to-analog converter (DAC), by using the algorithm described
below. The DAC converts the digital value to a current supplied to
the motor.

In the control system, as shown in the figure, the control loop
includes the microcontroller, the amplifier, the motor and its load.
The microcontroller contains the control algorithm for velocity loop
control.  To achieve the desired performance for the control system,
the parameters of the control loop are chosen to work with a
self-adjustable current amplifier and to compensate for certain plant
parameters, namely, inertia and friction.  The loop parameters are
designed in the frequency domain.  The bandwidth of the overall
control loop is chosen to be much lower than the commutation control
freque...