MODELLING & COMPENSATION OF PIVOT FRICTION IN A DISK DRIVE ACTUATOR

Abstract

With the increase in drive capacity and reduction in form factors, friction in the disk drive actuator pivot is becoming a significant problem. It results in unwanted overshoots, large settling times and steady state errors during head positioning. In this thesis, a friction model consisting of Stiction, Coulomb and Viscous friction is used to represent the pivot friction. Experimental measurements were also done to. better characterise the friction. For friction compensation, a discrete time disturbance observer is incorporated into a conventional state estimator/state feedback control structure to overcome the problem. Slight modifications were made to the discretizing process to improve the friction compensation. Simulations were done in MATLAB and results were compared with normal state feedback controllers. Frequency domain analysis is performed to study the characteristics of the control algorithm. Effects of resonance were studied and the control algorithm is also merged with the PTOS algorithm for seeking. Time and frequency domain simulations show that the proposed disturbance observer method greatly improves friction compensation while preserving the desired properties of conventional controllers.