Unknown disturbance estimation by sliding mode observer and compensation control for a dual-stage actuator system

In the present paper, a disturbance estimation and compensation problem is considered using the dual-stage actuator system of a hard disk drive as a plant. In addition, an unknown input disturbance observer based on a sliding mode observer (SMO) is proposed. The observer is designed based on the Edwards' method with modifications for the purposes of application to the control plant and performance improvement. One of the modifications is to introduce an additional output in order to satisfy the design assumptions of the SMO. The other modification is a design procedure of the additional output that is proposed in order to improve the disturbance estimation performances. The estimated disturbance is used as the compensation signal of the control input. The effectiveness of the proposed method is verified through numerical simulations. The simulation results revealed that the disturbance observer can estimate unknown disturbances and that the positioning performance is significantly improved by the compensation.