Frequency-shaped sliding mode control for flying height of pickup head in near-field optical disk drives

To achieve stable flying height of a pickup head in near-field optical disk drives, this study investigates a discrete sliding mode control with a frequency-shaped sliding surface. A compensator is introduced in a sliding mode using a frequency-shaped performance index with linear quadratic optimal and sliding mode control. As an actuator, a piezoelectric bender is used in this study to complement an air bearing at the head/disk interface. Experiments are carried out to demonstrate that the proposed controller performs better in flying height control than an optimal sliding mode controller. Accordingly, the controller can achieve stable flying height control in the presence of certain frequency vibration of optical disks.