| 摘要 |
PURPOSE:To realize an automatic release even if a focus servo-system falls into disorder, by operating a trigger circuit, providing a generated pulse, and returning a focus system into a leading-in range, when a detecting output of a reproducing signal exceeds a reference value and drops. CONSTITUTION:When a focus is shifted, an output signal F of a reproducing signal detecting circuit 12 drops, and when it exceeds a reference value Vr, a signal G of a level comparing circuit 13 is inverted to H, a trigger circuit 15 operates, an oscillating output H of a fixed period is generated, and the signal H is supplied to a focus coil driving circuit 11 through a pulse shaping circuit 17. Accordingly, an output signal H of the circuit 17 is added to a focus control signal B and is inputted to the circuit 11. As a result, an output signal of the circuit 11 is varied comparatively large, by which a focus coil 3 is driven, therefore, an objective lens is moved forcibly into a leading-in range, shift of the optical system is returned to the leading-in range, the focus servo-system operates and becomes a relocked state. |
