Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1998-12-10
2001-10-02
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S124150
Reexamination Certificate
active
06298024
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical disc devices for reproducing information recorded on various types of optical discs, and more particularly relates to optical disc devices capable of easily identifying the types of the discs in a short time.
BACKGROUND OF THE INVENTION
Japanese laid-open publication (Tokukaihei) No. 3-207056 discloses a method of identifying the types of discs for optical disc devices using various types of optical discs. In this method, specific information signals (type identifying signals) recorded on the respective optical discs in advance are read out so as to identify various types of optical discs, more specifically to distinguish a music-use CD (compact disc) and a computer-use CD-ROM.
According to the method disclosed in the Japanese publication No. 3-207056, since information recorded on a disc is actually read out to identify the disc, it is possible to accurately identify the disc. However, in order to identify the type of disc, it is necessary to control the rotation speed of the disc to be a predetermined value and to control the focus servo and tracking servo when reading the information from the disc. Thereafter, by reading out information called “TOC” (table of contents) recorded in the innermost periphery section of the disc, the type of the disc is first identified. Then, the operation of a processing system is switched according to the result of the identifying process. Therefore, this method causes an increase in a so-called “starting time”, that is the time taken from identification of the type of the disc to the completion of switching the operation of the device, including switching the processing system, performed after the identifying process.
Hence, in an optical disc device using various types of optical discs, even if the basic physical properties of discs, such as the signal frequency and recording density of the recorded information or the rotation speed and linear velocity, etc. of the discs, are substantially the same like in a music-use CD and computer-use CD-ROM, a long time and a number of processes are required to start the optical disc device.
In an optical disc device using various types of discs (for example, CD and DVD (digital video disc)), which are different from each other in their physical properties, particularly in the recording density and track pitch, to a greater degree than the degree of the difference between a music-use CD and a computer-use CD-ROM, it is often necessary to perform the process of switching an optical system of an optical pickup in order to obtain better signal reproduction characteristics in some cases. There also may be a possibility that there is a difference in the linear velocity, i.e., the rotation speed of the disc, between discs having different physical properties. In such a case, it is necessary to increase or decrease the rotation speed of the disc. Of course, the above-mentioned processes can only be carried out after identifying the type of a disc. As a result, it takes a long time to start the optical disc device.
As described above, with the prior art disclosed in the above-mentioned publication concerning an optical disc device for reproducing information recorded on various types of optical discs, a long time is required to identify the type of disc and an additional time-consuming process needs to be performed in accordance with the result of the identifying process. Thus, this technique suffers from a problem that the starting time of the optical disc device becomes longer.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical disc device capable of reproducing information from various types of optical discs whose physical properties, particularly information recording densities and track pitches, are different from each other to a great degree, identifying the types of the optical discs in a short time, and shortening the starting time.
In order to achieve the above object, an optical disc device of the present invention is an optical disc device for reproducing information recorded on an information track of an optical disc, and includes:
a pickup for applying a light beam to an information-recorded side of the optical disc, receiving light reflected from the information-recorded side, and outputting a readout signal based on the quantity of the light received;
an amplitude indicating signal generating section for generating an amplitude indicating signal varying-according to a change in the amplitude of the readout signal which occurs when the light beam is displaced relative to the information track in a radial direction of the optical disc; and
an identifying section for identifying the type of optical disc based on the density of information tracks in a radial direction of the optical disc by comparing the difference between the maximum value and the minimum value of the amplitude indicating signal with a predetermined value.
In the optical disc device, the amplitude of the readout signal output by the pickup according to the quantity of the reflected light is the difference between the peak value and the bottom value of the readout signal. The amplitude of the readout signal increases when the light beam is positioned just above the information track. Meanwhile, the amplitude of the readout signal decreases when the light beam is displaced from the center of the information track in a radial direction of the optical disc because the contrast of the quantity of the reflected light becomes smaller.
The amplitude of the readout signal becomes smaller with a decrease in the ratio of the area of the information track irradiated with the light beam to the total area irradiated with the light beam. On the other hand, the amplitude of the readout signal becomes larger with an increase in the ratio of the area of the information track irradiated with the light beam to the total area irradiated with the light beam. Therefore, when moving the light beam relative to the information track in a radial direction of the optical disc, the amplitude of the readout signal increases at the time the light beam is positioned just above the information track, and decreases at the time the light beam is positioned between two adjacent information tracks. Thus, the increase and decrease of the amplitude occurs repeatedly.
Hence, when the density of the information tracks of the optical disc in a radial direction of the optical disc is low, the ratio of the area of the information track irradiated with the light beam to the total area irradiated with the light beam is small at the time the light beam is positioned between two adjacent information tracks. As a result, the amplitude of the readout signal from this area is very small. Accordingly, the amplitude changes greatly when the light beam is moved relative to the information track in a radial direction of the optical disc. Consequently, the changes in the amplitude of the readout signal appear clearly, and variations in the amplitude indicating signal, which represent the changes in the amplitude, also are clear.
When the density of the information tracks of the optical disc in a radial direction of the optical disc is high, even if the light beam is positioned between two adjacent information tracks, the ratio of the information track irradiated with the light beam to the total area irradiated with the light beam is not as small as the ratio in the above-mentioned case. Therefore, the amplitude of the readout signal from this area is not as small. Consequently, the changes in the amplitude of the readout signal when the light beam is moved relatively to the information track in a radial direction of the optical disc is not as large. As a result, the variations in the amplitude indicating signal output by the amplitude indicating signal generating section are not as clear as the variations observed when the density of the information tracks is low.
Hence, by comparing the difference between the maximum value and minimum value of the amplitude indicating signal with a pred
Conlin David G.
Dike Bronstein Roberts & Cushman IP Group
Huber Paul W.
Sharp Kabushiki Kaisha
Tucker David A.
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