Patent ID: 7636285
Filing Date: 2009-12-22
Classification: G11B

Abstract:
1. An apparatus for inspecting an optical disc having multiple recording layers including first and second recording layers adjacent to each other, the second recording layer having a signal recorded area and a signal unrecorded area, wherein a boundary between the signal recorded area and the signal unrecorded area is at a prescribed address on a track on the second recording layer, the apparatus comprising: an optical pickup for applying a main laser beam to the optical disc, for focusing the main laser beam on one of the multiple recording layers, and for receiving reflected light caused by reflection of the main laser beam at the one of the multiple recording layers to reproduce a recorded signal from the one of the multiple recording layers; a first photodetector provided in the optical pickup for receiving a main reflected beam caused by reflection of the main laser beam at the one of the multiple recording layers; a second photodetector provided in the optical pickup and separated from the first photodetector; first means for detecting a level of a signal generated by the second photodetector in response to reflected light caused by reflection of the main laser beam at the second recording layer and incident to the second photodetector when the optical pickup reproduces a recorded signal from the first recording layer; second means for detecting an address of a currently-accessed position in a track on the first recording layer from a signal generated by the first photodetector in response to reflected light caused by reflection of the main laser beam at the first recording layer and incident to the first photodetector when the optical pickup reproduces a recorded signal from the first recording layer; third means for obtaining a reference address in the first recording layer, the reference address corresponding to a position radially coincident with a position at the prescribed address in the second recording layer; fourth means for calculating an allowable error limit address in the first recording layer from the reference address, the allowable error limit address corresponding to a position radially separated from the position at the reference address by a distance determined by an allowable error range; fifth means for detecting that the address detected by the second means reaches the allowable error limit address when the optical pickup reproduces a recorded signal from the first recording layer; sixth means for deciding whether or not the level detected by the first means is substantially equal to a reference level when the fifth means detects that the address detected by the second means reaches the allowable error limit address, the reference level being equal to a detected level obtained by the first means when the sub photodetector receives reflected light caused by reflection of the main laser beam at the signal recorded area in the second recording layer; and seventh means for concluding that a misalignment between the tracks on the first and second recording layers is within the allowable error range in cases where the sixth means decides that the level detected by the first means is substantially equal to the reference level.