| 摘要 |
<p>Automatic focus tripping device in an apparatus for reading information from a recording medium (9) having a flat reflecting surface such as a video disc or the like, in which the impact of an objective lens system with the medium (9) is prevented in an automatic focusing unit optimizing the distance between the medium (9) and the objective lens (10). In the automatic focusing unit the objective lens (10) focuses the light incident onto the medium (9) and also its reflected light, and an electromagnetic drive unit (7) is provided to drive the objective lens in the direction of the optical axis, means (12), (13), (14), (15) is provided for applying a drive signal to the drive unit (7), on which is superimposed a high frequency signal which does not obtain a response from the drive unit to a low frequency triangular waveform signal input to the drive unit (7) until the automatic focusing unit starts to operate normally, thereby controlling the automatic focusing after the lens (10) is moved into a prescribed region and preventing the impact of the lens (10) with the medium (9) without using a precise regulating mechanism.</p> |
