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