Method for gradually closing down a focus control loop of an optical drive system

An apparatus for operating an optical drive system (12) capable of reproducing/recording information from/to an associated optical carrier (1), wherein the apparatus comprises:

• a radiation source (5) for generating a radiation beam,
• a focusing means (3) for focussing the radiation beam,
• an optical receiver means (6) for generating an electric read signal in response to radiation reflected from the optical carrier (1),
• a focus tracking system (4, 7, 9) for tracking the carrier (1) with said focussed radiation beam (2),
• wherein said focus tracking system comprises
• a focus error generating means (7) for generating a focus error signal (FE),
• a focus actuator means (4) for changing a focus position of said focussed radiation beam (2) relative to the optical carrier (1), said focus actuator means (4) being driven by a supplied correction signal (CS), and
• a correction signal generating means (9) comprising
• a focus controller means (PID) for controlling said focus actuator, and, said focus controller means being supplied with said focus error signal (FE), and
• a focus memory loop (ML) for applying a stored correction signal to said focus actuator,
• and the apparatus further comprises:
• a) event detection means for generating a signal indicative of the occurrence of an event that requires at least a gradual stop of said focus tracking system (4, 7, 9),
• b) switching means (33) for disabling the focus controller means (PID) by opening the control loop,
• c) adjusting means (29) for gradually reducing a memory loop parameter of said focus memory loop (ML), said parameter corresponding to an amplitude of said stored correction signal,
• and optionally,
• d) adjusting means (31,32) for reducing a controller parameter of an integrating means (I) of said focus controller means (PID), said parameter corresponding to a focus offset position.