Disc drive apparatus

Method for determining focal offset error (FOE) in an optical system (30) of an optical disc drive apparatus (1), the optical system (30) comprising:

• beam generator means (31) for directing a light beam (32) towards an optical disc (2);
• an optical detector (35) for receiving a reflected light beam (32d) and for generating an detector output signal (SR);
• an objective lens (34) arranged for focussing the light beam (32b) in a focal spot (F) on an information layer of the disc (2), the objective lens (34) being displaceable in a direction perpendicular to the optical axis of the light beam (32);
• the method comprising the steps of:
• detecting a signal representative for the actual lens shift (LS);
• calculating the actual focal offset error (FOE) from said lens shift (LS) representing signal on the basis of a predetermined relationship between focal offset error (FOE) and lens shift (LS).

Method for determining focal offset error (FOE) in an optical system (30) of an optical disc drive apparatus (1), the optical system (30) comprising:

• beam generator means (31) for directing a light beam (32) towards an optical disc (2);
• an optical detector (35) for receiving a reflected light beam (32d) and for generating an detector output signal (SR);
• an objective lens (34) arranged for focussing the light beam (32b) in a focal spot (F) on an information layer of the disc (2), the objective lens (34) being displaceable in a direction perpendicular to the optical axis of the light beam (32);
• the method comprising the steps of:
• determining a direct relationship between focal offset error (FOE) and at least one signal component (Px;Py) derivable from the detector output signal (SR);
• processing the actual detector output signal (SR) to calculate said at least one signal component (Px;Py);
• calculating actual lens shift (LS) from said at least one signal component (Px;Py) on the basis of said direct relationship.

Method for controlling an axial position of an objective lens (34) in an optical system (30) of an optical disc drive apparatus (1), the optical system (30) further comprising:

• beam generator means (31) for directing a light beam (32) towards an optical disc (2);
• an optical detector (35) for receiving a reflected light beam (32d) and for generating an detector output signal (SR);
• the objective lens (34) being arranged for focussing the light beam (32b) in a focal spot (F) on an information layer of the disc (2), the objective lens (34) being displaceable in a direction perpendicular to the optical axis of the light bema (32);
• the method comprising the steps of:
• generating a reference signal (SREF) representing a desired amount of focal error;
• generating a focal error signal (SFE) representing the actual focal error;
• generating a focal offset error signal (SFO) representing the actual focal offset error (FOE);
• adding the focal offset error signal (SFO) to said reference signal (SREF), and subtracting said focal error signal (SFE), to obtain a result signal (SRES);
• generating an focal actuator control signal (SCF) on the basis of said result signal (SRES=SREF+SFO−SFE).