External Disturbance Rejection by Use of an Add-On Nonlinear Controller in HDD Servo Systems

A novel control method with an add-on nonlinear feedback controller is proposed in this paper to work together with the existing linear controller to deal with external disturbance in hard disk drive (HDD) systems. In the proposed control scheme, the capability of disturbance rejection is boosted when the tracking error of the control system gets larger due to the external disturbances. The stability of the proposed scheme has been proved, and chassis tests on several commercial notebook PC models showed that the proposed method is effective to handle wide-band vibration. Moreover, the implementation of the proposed scheme is very simple and may be even simpler than the linear controller.