A tracking motion approach for a piezotube actuator in a disk drive subject to disk deformation and disturbance

Abstract

This study investigates the disk drive dynamics when a disk surface deforms and a disturbance force is exerted on a pickup head in near-field optical disk drives. Serving as an actuator, a piezotube is connected to the suspension of the pickup head. A model is constructed to investigate the pickup head dynamics. Equations of motion for focusing and track-following are derived in the presence of disk surface deformation and the disturbance force on the pickup head. A proportional and derivative control method is carried out in numerical examples. There exists a critical proportional gain that influences the number of resonances in the frequency spectra. Numerical results show that there is only one resonance or none in the frequency spectra when the proportional gain is larger than the critical proportional gain. Hence, the tracking error ratio becomes smaller than one within a wide frequency range, if few resonances appear in the frequency spectra.