| 摘要 |
PURPOSE:To prevent a lens means from approaching a disc by providing a photodetector which is arranged in a position within the range of an optical beam reflected from the disc when an incident optical beam is out of control of a focus control means. CONSTITUTION:The optical beam is made incident on the disc through an object lens, and the reflected light is received by a photosensitive part 9. The photosensitive part 9 has photodetectors 9A-9D adjacent to one another and photodetectors 9E and 9F which are arranged in positions within the range of the optical beam reflected from the disc when the incident optical beam is out of focus control. Output signals of photodetectors 9A-9F are supplied to adding circuits 11, 12, and 26 of a signal processing part 10. The focus control is performed by a focus error signal Sf from a subtracting circuit 13, and an output signal Ss as a reproduced information signal component is obtained by an adding circuit 14. An addition signal Sx from the circuit 26 is supplied to a comparing circuit 22 and is compared with a reference voltage to stop the operation of a focus control means 7, and thus, the object lens is prevented from approaching the disc. |
