A new approach to the design of mode switching control in hard disk drive servo systems

In a modern large-capacity magnetic hard disk drive (HDD), both fast track seeking and perfect positioning of the read/write head are required. Mode switching control (MSC) approaches are widely used to meet these requirements. This paper proposes a new approach in designing MSC with an application to HDD servo systems. The proposed scheme uses a proximate time-optimal servomechanism in the track seeking mode, and a robust perfect tracking (RPT) controller in the track following mode. Unlike the conventional MSC approaches, the new method does not require an initial value compensation during mode switching. This is because the RPT controller in the second stage is capable of rendering the Lp-norm ð1ppoNÞ of the resulting tracking error arbitrarily small in the presence of external disturbances and initial conditions. Simulation and experimental results show that the proposed method improves the seek and settling time by about 10% over the conventional approaches.r 2002 Elsevier Science Ltd. All rights reserved.