A nonlinear dynamic filter to improve disturbance rejection in optical storage drives

To improve the low-frequency disturbance rejection properties of a DVD drive subjected to harmonic shocks, a variable gain control design in combination with an additional notch filter is suggested. A nonlinear control design is applied to overcome the trade-off between disturbance rejection and measurement noise sensitivity. Hereto the loop gain is increased beyond a threshold value for the radial error signal. To extend the current variable gain limitation, an additional notch filter is introduced. By tuning the notch filter parameters, stability is guaranteed way beyond the gain values obtained in the filter´s absence. Stability is studied globally on the basis of absolute stability theory and locally via numerical computation. The resulting performance is studied numerically on the basis of a nonlinear sensitivity analysis.