Adaptive inverse control for pickup head flying height in near-field optical disk drives

Near-field optical disk drives represent a novel technique for optical data recording. To achieve high precision in focusing for near-field data recording, it is essential to develop servo systems that can maintain a constant flying height. This study uses a piezoelectric bender can compensate the vibration of rotating optical disk. Due to the hysteresis phenomenon in piezoelectric material, adaptive inverse control is developed to overcome the nonlinear effect. The control scheme is implemented with least mean square sensed adaptive filter. Using a laser Doppler vibrometer for sensing, experimental results demonstrate that the present method results in only 2% displacement error in tracking command signals.