Abstract
The head positioning servo control of magnetic disk drives has been required to achieve both precise positioning and fast access. In order to meet these requirements, the Mode Switching Control (MSC) structure that includes several different structure controllers and switching functions has been widely used. In the MSC, each servo controller can be designed optimally, so the remaining issue is “switching.”
The MSC is a kind of Variable Structure Control System, but the switching is in one direction. This means that the servo mode is handed over from one to the other during a single servo action. So when the mode is switched from seek mode to track following one for example, this switching time is an initial time for the track following mode. As a result, the Initial Value Compensation (IVC) which is a method that considers the initial states, can be applied. The authors previously proposed the design method of this IVC and showed its effectiveness using disk drives servo control.
In this paper, we propose a new IVC method using additional input. When the servo mode is switched, an additional input which is an impulse response of initial values of the plant state variables, is added. The transfer function of the impulse response can be designed in order to not only cancel undesired poles of the transfer function from initial states to head position, but add desired poles as well. Therefore the transient response after mode switching can be much improved from the previous method. Also this IVC never influences the stability and sensitivity of the closed loop. Several experimental results show the effectiveness of this method.
