Two degree-of-freedom control with adaptive robust control for hard disk servo systems

A two-degree-of freedom (2DOF) control structure is proposed for read/write head servo systems of hard disk drives (HDD). This structure may be applied to both track seeking and track following, and it makes mode switches found in conventional HDD servo systems unnecessary. Two possible approaches are studied, emphasizing the rejection of disturbances and the effects of modeling uncertainties. One approach uses a disturbance observer (DOB), and the other uses adaptive robust control (ARC). Simulation results show that the 2DOF structure with ARC provides better performance than either the conventional servo system with mode switches or the 2DOF structure with DOB.