Enhancement of Short-Span Seeking in a Dual-Stage Seek-Track Following Control using Variable Saturation

Servo actuators used in hard disk drives have to
be able to move from one track to another track as fast as
possible in order to enable fast access to the data. This paper
improves short-span seeking performance of a recently proposed
compensator based control system for a dual-stage servo
actuator. Short-span seeking performance is improved by
replacing a constant saturation non-linearity in the secondary
loop of the dual-stage control system by a variable saturation
non-linearity. The variable saturation ensures secondary
actuator signal boundedness and at the same time modulates the
control error to be fed into the secondary control loop. This
results in a significantly faster response of the secondary actuator
and hence faster seeking times. The improvement in seeking
times is most significant for short range seeks that are within the
range of the secondary actuator. Both simulation and
experimental results comparing the performance of a dual-stage
servo actuator with constant and with variable saturation in the
secondary loop are presented. The use of a variable saturation
shows significant improvement in short-span seeking
performance