Switching control in blu-ray disk drives

To improve the nominal PID-controlled servo performances of a blu-ray disk drive, a switching observer is studied. Switching is done using a deadzone switching gain having the following properties: large-magnitude signals induce extra gain, small-amplitude signals do not. Additionally the observer part assures that large-magnitude signals induce extra low-pass filtering. As a result the design has low-frequency disturbance rejection properties resulting from high-gain feedback but with a favorable high-frequency noise response related to the properties of low-gain feedback. Robust stability is guaranteed using a Lyapunov characterization of input-to-state stability, whereas improved performances under vibrations and disk surface defects are demonstrated using two blu-ray disk drive setups.