| 摘要 |
<p>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 on either side of the exact focus point when a near to focus condition is achieved. The present system detects when the objective lens is at a near to focus condition in the range between bipolar voltage peaks on either side of the focused point. When the objective lens is near to focus where the known focusing system can maintain focus, the present system switches on the known focusing system. The present system monitors the focus condition and if a far out of focus condition occurs, waits a short time interval before activating a warning indication. Also, the present system waits a short time interval when a near to focus condition exists before activating the known focusing system in order to make sure that the near to focus condition is stable.</p> |
