Controller-Switching Strategy for HDD Servo Systems with Measurement Errors and Constraints on State and Control Variables



The head-positioning control system of a hard disk drive (HDD) must enable precise positioning and high-speed access. Mode switching control (MSC) has widely been used to meet these control requirements. One of the issues with MSC is how to determine the controller-switching strategy, which needs decisions on the controller's switching conditions and its initialization. We propose a method that utilizes initial value compensation (IVC) to determine the initial state of the controller. Although mode switching is non-linear, transient responses can be improved if the control system takes the initial state response after mode switching into consideration. IVC, which is based on this, can improve the transient response after mode switching. We also propose a method, which is based on the concept of a maximal output admissible set, of determining the switching conditions. It takes pointwise-in-time constraints and measurement errors in the plant's initial state into consideration. Experimental evaluations of the switching-control strategy we propose were undertaken with a 2.5-inch form-factor HDD. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.