Objective lens focus initialization system

In an optical data recording system of the type having an optical record carrier with a recording surface on which servo track portions are substantially concentrically positioned and radially spaced, an objective lens, a detector, a focus servo system including a focus servo control loop and a controller for opening and closing the focus servo control loop;

• a method for positioning the objective lens within focus capture range of the optical record carrier recording surface, including:
• cyclically driving the objective lens along a focus axis about a neutral position between offset positions while increasing displacement of the offset positions from the neutral position;
• and
• determining whether the objective lens is within focus capture range of the record carrier recording surface at each peak offset position by determining whether at least a predetermined first number of track crossings are detected within a predetermined first time period.

Apparatus for positioning objective lens means within focus capture range of an optical record carrier recording surface in an optical data recording system, including:

• an optical record carrier having a recording surface on which servo track portions are substantially concentrically positioned and radially spaced about a rotational axis;
• motor means for rotating the record carrier
• about its rotational axis;
• objective lens means for focusing a beam of radiation along a focus axis oriented generally perpendicular to the record carrier recording surface, and for collecting modulated radiation from the record carrier;
• tracking error detector means for producing a tracking error signal representative of position, along a tracking axis generally radially oriented with respect to the rotational axis, of the objective lens means relative to individual servo track portions;
• lens focus drive means for driving and positioning the objective lens means along the focus axis in response to focus drive signals;
• track crossing detector means responsive to the tracking error detector means for producing track crossing signals representative of relative motion, along the tracking axis, between the objective lens means and individual servo track portions of the record carrier;
• and
• focus capture control means responsive to the track crossing detector means for producing the focus drive signals in a manner causing the lens focus drive means to drive the objective lens means along the focus axis until the objective lens means is within focus capture range of the record carrier recording surface, and for determining whether the objective lens means is positioned within focus capture range of the record carrier recording surface as a function of the track crossing signals.