1. Field of the Invention
The present invention relates to an optical disk device that can record or reproduce data on or from plural types of optical disks, and a method for determining the type of a disk in the optical disk device.
2. Description of the Related Art
Optical disk devices can record or reproduce data on or from plural types of optical disks. Types of optical disks used in optical disk devices include, for example, CD (Compact Disk)-based disks (CD-ROM, CD-R, CD-RW, and the like), DVD (Digital Versatile Disk)-based disks (DVD-ROM, DVD-RAM, DVD-R, DVD-RW, DVD+R, DVD+RW, and the like), and HD-DVD (High Definition DVD) that uses a blue laser to record or reproduce data (hereinafter sometimes referred to as HD-DVD or simply HD). An optical disk device dealing with plural types of optical disks needs to determine the types of installed optical disks.
The following methods for determining a disk type have been documented.
A disk type determining apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 10-188458 determines the types of optical disks on the basis of the positions of reflection layers in each optical disk (CD or DVD) and the thickness of a transparent substrate formed on the reflection layers. The disk type determining apparatus detects a detection signal corresponding to a reflected light beam from an optical disk while moving an objective lens that condenses light beams, toward the disk. The detection signal varies depending on the number and positions of reflection layers in the optical disk. The disk type determining apparatus determines the type of the disk on the basis of a variation in detection signal, that is, the amounts of time required to detect a peak associated with specular reflection from the disk surface and a peak associated with reflection from the reflection layer.
An optical disk reproducing apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 9-330554 determines the disk type (CD or DVD) on the basis of a tracking error signal. When reproducing data from a second optical disk having a smaller track pitch than a first optical disk, the optical disk reproducing apparatus determines that this is not the first optical disk, on the basis of the tracking error signal. The disk type is determined by comparing the signal level of the tracking error signal with a predetermined threshold or counting the zero cross of the tracking error signal so that the determination can be made on the basis of the count value.
An optical disk device described in Jpn. Pat. Appln. KOKAI Publication No. 2002-32912 detects a normalized tracking error signal obtained by dividing an output from a tracking error signal detecting unit by an output from a reflected light quantity detecting unit; the tracking error signal detecting unit detects the positional deviation, in a radial direction of the optical disk, between a light beam and any of the tracks formed of recesses and projections on the optical disk, and the reflected light quantity detecting unit measures the quantity of light reflected by the disk. The optical disk device determines to which of the disk types involving different groove pitches (pit depth and track pitch) the disk belongs, depending on whether or not the maximum amplitude of a normalized tracking error signal obtained when a light beam traverses the disk in the radial direction has at most a predetermined value. The optical disk device also determines to which of the disk types involving different track pitches the disk belongs, by comparing the number of tracks with a sine wave that synchronizes with eccentricity.
An optical disk device described in Jpn. Pat. Appln. KOKAI Publication No. 9-204729 irradiates recording layers in the optical disk with a laser beam for signal read, and scans the laser beam for signal read over a given range in the radial direction of the optical disk. The optical disk device detects the number of tracks on the basis of signals read, by the scan over the given range, from the optical disk recording layers present within the given range, to determine the type of the optical disk on the basis of the number of tracks.
A disk type determining apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 10-188458 determines the type of the optical disk (CD or DVD) on the basis of the thickness of a base material forming the optical disk and the number of reflection layers in the optical disk. Since CD and DVD have different base material thicknesses, the method described in Jpn. Pat. Appln. KOKAI Publication No. 10-188458 can determine the disk type.
However, this method cannot distinguish DVD from HD-DVD because they have the same base material thickness and the same number of reflection layers. A simple method for determining whether the disk is DVD or HD-DVD is to record or reproduce data on or from a disk of an assumed type, and if the recording or reproduction has been properly achieved, to determine that the disk is of the assumed type. However, if the optical disks have different recording densities (track pitch and pit size), data recording or reproduction must be executed with laser wavelength, NA (Numerical Aperture) of the objective lens, demodulation algorithm, or the like switched depending on the type of the optical disk. Consequently, to determine to which of a plurality of disk types the optical disk belongs, data recording or recording must be executed with the laser wavelength or the like switched depending on the type of each disk. This increases the time required to determine the disk type.
Further, the methods for determining the disk type described in Jpn. Pat. Appln. KOKAI Publication Nos. 9-330554, 2002-32912, and 9-204729 determine the disk type on the basis of the tracking error signal. These methods thus need to properly read the tracking error signal.
However, the large difference in base material thickness between CD and DVD (HD-DVD) leads to optical aberration, which prevents the proper focus error signal from being obtained. This may result in a failure in a focus on operation, which in turn prevents the proper tracking error signal from being obtained. Further, the accuracy of detection of the tracking error signal may be reduced by an error in installation of the optical disk in the optical disk device, eccentricity of the optical disk, or the like. Furthermore, a ROM-based optical disk (stamp media) on which data has already been recorded has a pit depth different from that of a recordable optical disk on which data can be recorded. This may vary the amplitude of the tracking error signal even among optical disks of the same type. This may in turn reduce the accuracy of determination of the disk type.
A blue laser for HD-DVD needs to be used to properly detect the tracking error signal from HD-DVD. However, if CD or DVD is irradiated with a laser beam for HD-DVD (blue laser beam), which has a large quantity of energy, a recordable or rewritable optical disk of CD or DVD may be damaged. Likewise, if CD is irradiated with a laser beam for DVD to detect the tracking error signal, it may be damaged. It is therefore difficult for the conventional techniques to determine to which of a plurality of disk types including HD-DVD the optical disk belongs, without damaging the optical disk.
An object of the present invention is to provide an optical disk device and a method for determining a disk type both of which can determine to which of different optical types the optical disk belongs, in a short time without damaging the optical disk.