| 摘要 |
PURPOSE:To protect information, and to execute an access at a high speed by flurring a beam spot by an optical head, at the time of holding after information is recorded, or after information is reproduced, and also fixing a position of the optical head to its place. CONSTITUTION:When a holding state elapses a prescribed time, a reference signal from a reference signal generating circuit 35 is supplied to a differential amplifier 34 by a switching signal from a CPU 50. As a result, a differential amplifier 38 outputs a tracking shift detecting signal which is obtained by taking a difference between a detecting signal from a photodetecting cell 22a, and a signal which is added the reference signal to a detecting signal from a photodetecting cell 22b. Next, the signal is brought to waveform shaping by a waveform shaping circuit 39 and supplied to a driving circuit 40. The driving circuit 40 supplies a prescribed current to a coil 24, drives an objective lens 16 in the vertical direction and moves it to a position shifted from a focussed point position. Also, the CPU 50 stops tracking by supplying a switching signal to a switching circuit 46, and also stops a linear motor by outputting a stop signal to a driving circuit 51.
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