A fast settling servo controller for high-density disk drives

Abstract

During seek operation in disk drives, the recording head is moved toward desired track by seek servo controller and then is settled onto the center of the desired track by settling servo controller. If the head speed at the start of settling servo controller is not slow, it may produce overshoot relative to the center of track and thus extend settling time. The degradation in settling performance will be more severe as the track width becomes smaller for high track density. In this paper we discuss the design of settling servo controller which provides fast settling performance without creating overshoot. It is well known that transient response will be much faster if slow poles are canceled out properly. In order to cancel unwanted poles, we apply a sequence of weighted discrete pulse signals to the system in addition to the state feedback control. For exact pole-zero cancellation, we consider the dynamics of power amplifier used for actuator current regulation and the effects of delay in control action. In addition, we present system parameter identification algorithm for the robustness of our controller to system parameter variation. In order to demonstrate the practical use of our controller, we present experimental results obtained by using a commercially available disk drive.