Patent ID: 6240055
Filing Date: 2001-05-29
Classification: G11B

Abstract:
A focus position adjustment device for an optical disc that includes a first shape track and second shape track, comprising:focus error detection unit for detecting a convergence condition of a laser beam that is directed at the optical disc, and for outputting a focus error signal that represents the convergence condition;focus control unit for changing a focus position of the laser beam according to the focus error signal so that the convergence condition is a predetermined condition;reproduction condition detection unit for detecting a reproduction condition of the optical disc according to a reproduction signal when information that has been recorded on the optical disc is read;track detection unit for detecting whether a laser beam spot is positioned on a first or second shape track, and for outputting a track identification signal that represents a track on which the laser beam spot is positioned; andfocus position detection unit that includes:a focus position renewal unit for determining a first renewed focus position with an improved reproduction condition according to the reproduction condition when the track identification signal represents a first shape track, and for determining a second renewed focus position with an improved reproduction condition according to the reproduction condition when the track identification signal represents a second shape track, wherein the focus position renewal unit judges whether the reproduction condition improves when the focus position is moved by a predetermined amount, and determines the first and second renewed focus position according to the judgment by the focus position renewal unit; anda focus error signal modification unit for modifying the focus error signal so that the focus position is the first renewed focus position when the track identification signal represents a first shape track, and for modifying the focus error signal so that the focus position is the second renewed focus position when the track identification signal represents a second shape track, wherein the focus control unit changes the focus position of the laser beam according to the modified focus error signal, wherein the reproduction condition detection unit detects an error rate in the reproduction signal as the reproduction condition, andwhen the track identification signal represents the first shape track, the focus position renewal unit determines the first renewed focus position so that the error rate is lower, and when the track identification signal represents the second shape track, the focus position renewal unit determines the second renewed focus position so that the error rate is lower.