Focus initialization system for optical recording

Abstract From the Canadian patent

A focus initialization system is provided for optical data recording of the type in which an objective lens relatively near to the optical recording media is moved back and forth in comparatively small excursions to maintain focus for the read beam and write beam on the media. This system initializes or loads a conventional focusing system by starting the objective lens at a position at the far end of its travel limit preferably with the objective lens furthest from the optical media. The objective lens moves slowly towards the optical media while the system operates to detect when a near focus condition exists. Known focusing detection systems produce a bipolar output voltage having a peak …