Abstract
The head positioning servo control on magnetic disk drives has been required to achieve both precise positioning and fast access. To satisfy these requirements, a Mode Switching Control (MSC) structure that includes several different structure controllers and switching functions has been widely used. Because the servo controllers can already be designed optimally, the only remaining issue is “switching”.
The MSC is a kind of Variable Structure Control System with switching in only one direction. This means that the servo mode is handed over from one mode to another during a single servo action. Thus when the mode is switched from seek mode to track-following mode, the switching time is the initial time when the track-following mode begins. As a result, Initial Value Compensation (IVC), a method that takes into account the initial state values, can be applied. The authors previously proposed the design for the IVC and showed its effectiveness in disk drive servo controls.
In this paper, we propose a design method for determining the optimal combination of initial states for mode switching. Here the H2-norm of a transfer function between initial values and control input, is defined as the performance index of the transient response after mode switching. By combining the IVC method with this method of determining the optimal switching conditions, it can be said the MSC design methodology has been completed. Several experimental results show the effectiveness of this method.
