| 摘要 |
PURPOSE:To ensure a steady and assured focus servo-action, by applying the opposite force to a lens according to the moving speed of the lens when the lens exceeds the desired distance or its vicinity. CONSTITUTION:The start signal and the servo error signal A are applied to the lens driving motor 4 via the adder circuit 3 and in the form of the positive phase input. The signal A is also turned into the adverse phase input of the motor 4. In such constitution, the lens is driven toward the recording surface, and the error signal A is supplied. The control signal D is delivered to the comparator 11 at the time point when the desired distance of the lens, i.e., the polarity of the error signal is reversed. The sampling switch is closed by the signal D, and the output B having the pulse duration according to the moving speed of the lens of the comparator 6 is applied to the motor 4 as the opposite force via the differentiating circuit 9 and the diode 10. In this instant, the loop switch 2 is opened by the signal D, and the lens is positioned nearly at the right place due to a low moving speed of the lens. As a result, the lock-in action can be performed smoothly for the servo. |
