PURPOSE: To realize a seek servo system whose reliability is high by restricting the lead-in position of an optical spot into track follow-up control to a specified range at the time of shifting from coarse seek to precise seek.
CONSTITUTION: As a relative speed between the optical spot 13 and a track deteriorates, the continuous time T of a track deviation zerocross pulse 4 gradually becomes longer and it reaches a prescribed value To at last. When a micro computer 40 recognizes that a track deviation window pulse 46 which a window comparator 39 generates previously comes to a low level or it comes to the low level by time waiting, the micro computer 40 turns off a coarse positioning control instruction signal 6 transmitted to an analog switch 33 through a control line 43 and turns off the contact point 3 of the switch 33. Then, the micro computer 40 turns of a track follow-up control instruction signal 7 and starts track follow-up control.
SAITO ATSUSHI
MIZOGAMI TAKUYA
| JPH0278021A | 1990-03-19 |