| 摘要 |
PURPOSE:To attain the stable focus control by discriminating a recording carrier set into a focus controller and switching the gain of a focus control system so as to secure the stable focusing state for the light beam on the recording carrier in response to the discriminating signal. CONSTITUTION:A discoid recording carrier 1 is attached to the rotary shaft of a disk motor 2 and revolved in a prescribed number of revolutions. A jacket 3 covers the carrier 1 for protection. A discriminator 4 consists of a light emitting diode and a photodetecting diode. The type of the carrier 1 is discriminated by detecting the form or the reflection factor of the jacket 3. A processing circuit 6 supplies the output of the discriminator 4 and delivers the signal corresponding to the type of the carrier 1. A synthesizing circuit 29 delivers the signal obtained by adding four outputs of a photodetector 16 and supplies it to dividers 32 and 37 via a gain switching circuit 43. The signal of a circuit 5 is supplied to gain switching circuits 33, 38 and 43, and these switching circuits change the amplification factor in response to the signal of the circuit 5. In such a way, the stable focus control is secured. |
