| 摘要 |
PURPOSE:To secure focus control by providing a means of starting, stopping and restarting the focus drawing operation of irradiating light according to the states of a focus control signal and a guide-track traverse signal. CONSTITUTION:When a signal FON is inputted to a terminal K, switches 24 and 26 turn on between terminals p2 and r2, and p3 and r3, allowing an aperture lens to approach a disk. When a focus error signal DI increases above the Vthl of a comparator and the disk is judged to be within focus drawing range, the signal Q1 of an FF29 goes down to an L to turn off switches 26 and 26, and a switch 22 turns on between terminals p1 and r1 to turn on a focus control loop I. As a recording material surface is brought under focus control, a guide- track traverse signal inputted to a terminal S decreases below the set value Vth2 of the comparator 37 and the delay pulse G of a delay pulse generating circuit 31 is intercepted by an AND gate 34 to hold a focus-controlled state, but when the signal S is high, the focus drawing operation is repeated through the output of the gate 34, thus performing the focus control securely. |
