| 摘要 |
The arm carrying the optical head that projects and focuses a light beam onto a record trace on a video disc record is provided with a tracking movement by mounting the arm on an electromagnetically driven moving coil system that produces torque, driving the arm radially of the disc in accordance with a combination of coarse and fine tracking correction signals. The light beam is deflected by mirrors both at the pivot of the arm and at its extremity. The mirror at the arm extremity is either associated with a focusing lens or else provided with a parabolic curvature so that the light beam will be narrowed to a spot on the record trace. For transparent records, a photocell on the other side of the record disc is carried on a second arm mounted on the same torque-producing moving coil system in a manner elastically rather than rigidly coupled to the moving coil structure. In a system for opaque discs, the arm extremity deflecting mirror is a half mirror and the photocell is mounted behind the half mirror. |
