Improvement of servo performance via nonlinear feedback control in hard disk drive servo systems

In hard disk servo systems, two or more types of controllers are used for track seek, track follow and track settling modes. Due to this nature there is a need to consider the problem of mode switching among these controllers. In this paper, a composite nonlinear feedback controller is used to perform the above functions. The goal of this paper is to propose a unified controller to perform different modes of operation in HDD servo system with the saturation constraints on control signal. This is by the design of composite nonlinear feedback control law based on a nominal linear controller. In the face of actuator saturation, this control law not only increases the speed of closed-loop response but also improves the settling performance.