Design and Implementation of Feedback Resonance Compensator in Hard Disk Drive Servo System: A Mixed Passivity, Negative-Imaginary and Small-Gain Approach in Discrete Time

Abstract

This paper presents a feedback resonance compensator designed in a simple and yet efficient way to suppress the effects of resonant modes of voice coil motor actuator used in hard disk drive (HDD) servo system. A velocity feedback controller is chosen as the feedback resonance compensator. Resonant modes of the actuator prohibit bandwidth to be pushed to higher frequencies and it causes large oscillations to the closed-loop system response. Therefore, effective compensation of mechanical resonant modes is one of the design challenges in HDD servomechanism. The proposed design is based on a mixed passivity, negative-imaginary and small-gain approach in discrete time which results in a robust stable controller. Firstly, stability of discrete-time interconnected system is analyzed using mixed passivity, negative-imaginary and small-gain properties. These results are analogous to previously established continuous-time case. Nowadays most of the control design is done in discrete time. Hence, this paper provides a base for discretization of mixed system with passivity, negative-imaginary and small-gain properties. Secondly, a velocity feedback controller for resonance compensation is designed using this mixed approach. Simulation and experimental results substantiate the effectiveness of the controller.