Patent ID: 8159924
Filing Date: 2012-04-17
Classification: G11B

Abstract:
1. An optical disc device comprising: a first beam source that emits a first optical beam corresponding to a first optical disc; a second beam source that emits a second optical beam that corresponds to a second optical disc and whose wavelength is different from that of the first optical beam; an objective lens that serves as a lens having a first numerical aperture when the first optical beam converges on a signal recording surface of the first optical disc while serving as a lens having a second numerical aperture when the second optical beam converges on a signal recording surface of the second optical disc; a drive section that drives the objective lens in a focus direction along which the objective lens moves close to or away from the optical disc; a signal processing section that generates a reflection optical signal based on the intensity of a reflection optical beam that is the first or second optical beam reflected by the first or second optical disc; a storage section that stores a first disc waveform representing the waveform of the reflection optical signal to be obtained when the first optical beam is emitted to the first optical disc while the objective lens is moved in the focus direction; and a type determination section that makes a determination as to whether or not an unknown disc, whose type is unknown, is the first optical disc based on a degree of matching between the first disc waveform and a first unknown disc waveform representing the waveform of the reflection optical signal obtained when the first optical beam is emitted to the unknown disc while the objective lens is moved in the focus direction, the type determination section calculating a convolution integral of the first disc waveform and the first unknown disc waveform to generate a degree-of-matching signal representing the degree of matching, and makes a determination as to whether or not the unknown disc is the first optical disc based on the signal level of the degree-of-matching signal, the type determination section determining that the unknown disc is the first optical disc when the signal level of a total correlation pattern is greater than or equal to a total correlation threshold, wherein the total correlation pattern appears in the degree-of-matching signal when there is a small difference in time between the first disc waveform and the first unknown disc waveform, and the type determination section generates the degree-of-matching signal by imputing, with respect to the first disc waveform, the first unknown disc waveform from the opposite side of a time axis and moving the first unknown disc waveform in the direction of the time axis; the type determination section assumes that a detection time starts at a time when a surface reflection pattern representing the surface of the first optical disc is detected in the first disc waveform and ends at a time when a recording surface reflection pattern representing the signal recording surface of the first optical disc is detected; and the type determination section recognizes a pattern appearing during a determination period as the total correlation pattern, wherein the determination period starts at a time when a surface correlation pattern indicating that the surface reflection pattern of the first unknown disc waveform has overlapped with the recording surface reflection pattern of the first disc waveform is detected and continues until the detection time has passed.