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 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