| 摘要 |
PURPOSE:To reduce focus errors by exercising focus control while the interval between a focusing element and record carrier is within a prescribed range all the time, by applying a means of controlling the position of the focusing element with the voltage required to hold the interval between the both in the prescribed range. CONSTITUTION:When focus control is not exercised, the interval between the surface of disk 5 and condenser lens 4 is much greater than a proper distance. In the start of the device, signals from lead-in range detecting circuit 14 to switches 10 and 11 are at L; switch 10 is turned on, switch 11 off. Simultaneously with the start of the device, lamp waveform generator 12 is supplied with a start pulse to develop an output voltage of 0V, and this generator 12 is further supplied with pulses from pulse generator 13, so that the output voltage increases in steps according to the number of the input pulses. The output of lamp waveform generator 12 is supplied to condenser lens driver 3 via condenser lens driving circuit 2 to move gradually condenser lens 4, which approaches disk 5 gradually. |
