Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-08-28
2001-05-08
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053130
Reexamination Certificate
active
06229772
ABSTRACT:
1. Technical Field
This invention relates to an optical disc device capable of coping with plural types of optical discs, and a method for discriminating optical discs.
2. Background Art
As optical discs, compact discs are in widespread use, such that optical discs of the CD type are used in many fields, to say nothing of the field of musical application. The CDs for music are usually designed as replay-only media. However, an overwrite type disc termed compact disc recordable (CD-R) is also commercialized.
On the other hand, an optical disc termed a digital versatile disc/digital video disc (DVD) has also been developed as an optical disc suitable for multimedia use. This DVD is proposed as being adaptable to a wide field of applications, such as for video data, audio data or computer data. The DVD, which is an optical disc of the same size as the CD (12 cm in diameter), has a significantly increased recording capacity.
Meanwhile, in keeping pace with development of a new optical disc, it becomes desirable to provide an optical disc device exhibiting interchangeability between conventional and newer types of optical discs.
As for the DVD, it is desirable to develop an optical disc device capable of coping with both the CD and the DVD. However, since the CD and the DVD differ in reflectivity depending on, for example, the difference in structure of the signal recording layer of the optical disc, the RF signals obtained by an optical pickup is varied in signal level, depending on the optical disc type, whilst optimum values of parameters of various servo systems, such as focussing servo or tracking servo systems, are also changed.
Therefore, an optical disc device, adapted for coping with plural optical disc types, is required to correctly discriminate the type of optical disc on loading the optical disc thereon.
If the disc is of the type in which an optical disc is housed in a cartridge, the disc type can be easily discriminated by providing a cartridge discriminating hole. However, if the optical disc is not of the type housed in a cartridge, and moreover the optical disc itself is of the same size, this mechanical discrimination system cannot be used.
Moreover, if special components or units are provided for discriminating the disc type, such as a sensor, the device is undesirably complicated in structure, while the manufacturing costs are also raised.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical disc device and an optical disc discriminating method in which plural optical disc types having different numbers of signal recording layers are discriminated and an operating mode corresponding to the optical disc type is set by control means based on the discriminating output for reliably reproducing the plural types of optical discs.
In one aspect, the present invention provides an optical disc device including a laser light source for radiating a laser light beam illuminated on a signal surface of an optical disc via an objective lens, photodetector means for detecting the light of the laser light radiated by the laser light source and reflected from the signal surface of the optical disc, focussing control means for displacing the objective lens responsive to the focussing error signals generated on the basis of a detection output by the photodetector means for controlling the focussing state of the beam spot of the laser light bam on the signal surface, disc discrimination means for discriminating the types of the optical discs, based on the focussing error signals, when the objective lens is moved by the focussing control means along the optical axis for focussing search and control means for setting an operating mode in meeting with the disc types based on a discrimination output by the disc discrimination means.
With the optical disc device of the present invention, photodetector means has a photodetector split in at least four segments. The focussing control means performs focussing control, based on a focussing error signal FE=(A+B)−(C+D) in which A, B, C and D denote detection signals of the four segments of the photodetector. The disc discrimination means generates a gating pulse by converting a sum signal PI=A+B+C+D of the detection signals A to D of the photodetector at a pre-set level into binary-valued signals at a pre-set level. The disc discrimination means converts the focussing error signals FE into binary-valued signals for generating discriminating pulses. The disc discrimination means counts the discriminating pulses for discriminating the disc types having different numbers of recording layers based on the counted results.
In the optical disc device of the present invention, the disc discrimination means sets a threshold level for the above conversion-to-binary operation responsive to, for example, the window width proper to the gate pulse.
Also, in the optical disc device of the present invention, the disc discrimination means detects the distance between the optical disc surface and the signal surface based on a detection output of the photodetector means to discriminate plural optical discs having different substrate thicknesses based on this detected distance.
Also, in the optical disc device of the present invention, the disc discrimination means discriminates the types of the optical discs based on an output timing of the photodetector means during the time of outputting of focussing search signals for shifting the objective lens along the optical axis.
Also, in the optical disc device of the present invention, the disc discrimination means detects whether an optical disc to be discriminated is a one-layer disc having a sole signal surface or a double-layer disc having two signal surfaces, based on, for example, the above focussing error signals.
Also, in the optical disc device of the present invention, the disc discrimination means detects the types of plural discs with different numbers of the signal recording layers based on the focussing error signals detected during the time the focussing control means shifts the objective lens in a direction approaching to the optical disc.
Also, in the optical disc device of the present invention, the disc discrimination means detects whether the optical disc to be discriminated is a first optical disc having a first thickness or a second optical disc having a second thickness smaller than said first thickness based on a detection output by said photodetector means.
The optical disc device of the present invention includes convert-to-binary means for converting the focussing error signals to binary signals by comparing the signal level of the focussing error signals to pre-set positive and negative levels and detects the type of the optical disc by checking the number of times of occurrences of the binary focussing error signals.
The present invention also provides an optical disc device in which a laser light beam is radiated via an objective lens so as to be illuminated on a signal surface of the optical disc to reproduce signals recorded on the signal surface, including focussing control means for shifting the objective lens from a first position remote from the optical disc to a second position approaching to the optical disc and disc discrimination means for discriminating whether the optical disc is a single-plate disc or a laminated disc based on the reflected light from the disc surface and the reflected light from the signal recording surface detected during the time interval when the objective lens is moving from the first position to the second position and disc discrimination means for discriminating whether the disc is the single-layer disc or a double-layer disc based on the focussing error signals detected during said time interval.
In another aspect, the present invention provides a method for discriminating an optical disc including a generating step of illuminating a laser light beam on a signal surface of the optical disc via an objective lens, a generating step of detecting the reflected light
Kumagai Eiji
Nagashima Kenji
Tsukada Futoshi
Smith Andrew V.
Sony Corporation
Tran Thang V.
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