| 摘要 |
After making such adjustment that an a main push-pull signal MPP offset can be made zero when a main beam is positioned at the center of a main photoreceptor, using electric signals E and F photoelectrically converted by one of two two-divided side beam photoreceptors and electric signals H and G photo-electrically converted by the other thereof, a side push-pull signal SPP including a constant alpha is determined for allowing respective (F-alphaE) and (alphaH-G) offsets to be made zero and is calculated according to the formula, SPP-(F-alphaE)+(alphaH-G). From this SPP signal and the main push-pull signal MPP, a differential push-pull signal DPP is then calculated, thereby allowing stable tracking control to be carried out, even during recording.
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