| 摘要 |
PURPOSE:To drive a motor securely into a focusing state by detecting whether or not a synchronous detection output which becomes a signal for driving the motor is nearly fixed in phase and its amplitude is within a specific range for a certain time, and supplying the synchronous detection output or alternate signal to the motor or varying a loop gain according to the detection result. CONSTITUTION:When a lens 1 comes close to a focusing point and a reference frequency component becomes small, the output amplitude of a synchronous detecting circuit 10 decreases gradually. At this time, if its output level enters the blind sector of the motor 12 and the motor 12 stops, the synchronous detecting circuit 10 outputs a signal which has the same polarity and level continuously. A comparing circuit 13 or 14, therefore, outputs logic 1 continuously according to the polarity. This is detected by a shift register and an AND circuit and sent to a control circuit 19. The control circuit 19 connects a switch 20 to a battery 21 or 22 for a constant time according to whether the detection result is sent out of an AND circuit 17 or 18. Consequently, the values of the batteries 21 and 22 are set larger the blind sector, and then the motor 12 moves in a focusing direction. |
