| 摘要 |
PURPOSE:To eliminate influecnces of disturbance caused by external light and oscillation, eccentricity, etc., of a high-density rotary disk, by detecting the reflecting light of an optical beam which oscillates and scans with a prescribed frequency and performing synchronism detection on signals related to the frequency of the detected signals with signals having the same frequency component. CONSTITUTION:A light spot 30 oscillates at a frequency (f) by means of an optical deflector 31 and the 62 of the figure shows its oscillating locus. The output signal 15 of a photodetector 34 is inputted into a band-filter 19 and the original beam spot oscillating frequency component (f) of an envelope 14 is fetched and inputted into a synchronous rectifying circuit 38. On the other hand, the signal of an oscillator 18 is used as the reference voltage of the circuit 38 through a phase adjusting circuit 17. The output signal of the synchronous rectifying output signal and the signal of the oscillator 18 are added to each other by an adder circuit 16 and the output signal of the circuit 16 becomes a drive signal containing a DC component and frequency (f). When a disk rotates with the oscillating center line 61 of the light spot 30 being always coincident with the center line 60 of an information groove 25, the DC component of the drive signal becomes zero, but, when the center line 61 does not coincide with the center line 60, a positive or negative DC component is produced and the light beam is controlled so that the center lines 61 and 60 can coincide with each other. |
