| 摘要 |
PURPOSE:To raise the recording density without reducing the relative position error signal level by switching the polarity of the relative position error signal to actually raise the pitch of only information tracks twice. CONSTITUTION:A polarity inverting means 12 arbitrarily switches the polarity of the relative position error signal. In case the output signal has the same polarity as an input signal, the output signal of the polarity inverting means 12 is amplified by an actuator driving means 10, and a focus lens 6 is moved by an actuator 11 to match the position of a light spot to the first information track 2a of a recessed part (viewed from the side opposite to a light source) of a guide groove. That is, servo is applied to a point A in a figure. If the relative position error signal has the polarity inverted by the polarity inverting means 12 and is applied to the actuator driving means 10, tracking servo functions so that the light spot is matched to the second information track 2b of a projecting part of the guide groove at this time, and information of the information track 2b is read out. That is, servo is applied to a point B in the figure.
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