OPTICAL DISC FOCUSSING ACTUATOR CONTROL AT OPTIMAL BANDWIDTH

摘要

A method and apparatus for a feedback loop (30) used with a servo controller (14) to control an actuator (13, 17) of an optical disc drive. The gain (18) in the feedback loop (30) determines the bandwidth of the actuator (13, 17) in accordance with predetermined parameters for predetermined intervals. High rotational disk speeds, especially during writing, necessitate that the actuator servo controller feedback loop have a high loop gain and can become critical. Higher gains will cause oscillations in the loop. Loop gain spread from sources such as detector sensitivity differences on recorded and non recorded areas, is controlled by setting the control gain at an initial value lower than the maximal value in order to avoid oscillations. The control gain is then adjusted to a maximum value by means of an AGC mechanism. This AGC mechanism is activated for short periods of times to adjust the gain.