Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1998-08-25
2001-06-05
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S044270, C369S053230
Reexamination Certificate
active
06243341
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of distinguishing disks, and particularly relates to a method of distinguishing a particular type of disk from different types of disks on which signals are recorded in different formats respectively, according to an output from an optical pickup.
2. Description of the Background Art
It is important to make a DVD (Digital Video Disk) reproduction apparatus compatible with CD (Compact Disk) reproduction in view of utilization of abundant soft resources of the CD. Therefore, an art of providing the DVD reproduction apparatus with a compatible CD reproduction function is required.
Regarding the specifications of the CD and the DVD, they are different in the physical specification and the recording signal specification as shown in Table 1 and Table 2, and accordingly switching of the pickup and control thereof corresponding to respective disks are necessary.
TABLE 1
Physical Specification of Disk
DVD
CD
Disk Substrate Thickness (mm)
0.6
1.2
Disk Structure
two sheets attached
single sheet
Minimum Pit Length (mm)
0.4
0.83
Track Pitch (mm)
0.74
1.6
TABLE 2
Recording Signal Specification
DVD
CD
Signal Modulation System
8/16 modulation
8/15 modulation
Transfer Rate (Mbps)
11.08
2.03
The disc distinguishing methods interesting to the present invention are disclosed in Japanese Patent Laying-Open Nos. 61-42751 and 3-181062, for example.
According to a conventional method, a disk type is identified by the difference of reflectance for a light beam among recording media such as an optical disk. When disks having nearly the same reflectance such as the DVD and CD are to be distinguished, an allowable error of reference values are small to make it difficult to correctly distinguish them due to variation of an RF signal or the like.
Further, the level of a focus error signal for a dual DVD is low compared with that for a single DVD to be easily subjected to noises of a circuit or the like. Therefore, to physically distinguish between the dual DVD and the single DVD using the conventional method described above is difficult.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of distinguishing disks according to which those disks having almost the same reflectance can be correctly distinguished.
Another object of the present invention is to provide a method of distinguishing disks which is not easily subjected to the influence of noises.
Still another object of the present invention is to provide a method of distinguishing disks according to which a compact disk (CD) and a digital video disk (DVD) can be correctly distinguished.
Still another object of the present invention is to provide a disk reproduction apparatus by which control and setting according to disks with signals to be reproduced are possible without manipulation by an operator, and accordingly reproduction suitable for the disks is achieved.
The objects described above of the present invention are achieved by a method of distinguishing disks including the steps below. Specifically, the method of distinguishing disks according to one aspect of the present invention includes the steps of performing focus search operation with an optical pickup in a first disk reproduction state, detecting the maximum value and the minimum value of an output from the pickup obtained by the focus search operation to determine a first waveform level as a difference between the maximum value and the minimum value, performing focus search operation with the optical pickup in a second disk reproduction state, detecting the maximum value and the minimum value of an output from the pickup obtained by the focus search operation to determine a second waveform level as a difference between the maximum value and the minimum value, and comparing a ratio between the first waveform level and the second waveform level with a prescribed value.
Disks are distinguished from each other by comparing, a ratio between a difference between the maximum and minimum values of an output from the pickup obtained by the first disk focus search and a difference between the maximum and minimum values of an output from the pickup obtained by the second disk focus search, with a prescribed value. The ratio is determined correspondingly to respective disks irrespective of the reflectance. Therefore, it is possible to provide a method of distinguishing disks by which disks having nearly the same reflectance can be precisely distinguished.
According to another aspect of the invention, a method of distinguishing different types of disks is characterized in that the type of disk is identified based on the number of times peak-to-valley of a focus error signal repeats. The method includes the steps of comparing a sum of a first threshold value and a prescribed value with a focus error signal, changing a level of a binary signal when the focus error signal exceeds the sum, thereafter comparing a difference obtained by subtracting a second threshold value from a prescribed value with the focus error signal, changing the level of the binary signal when the focus error signal becomes smaller than the difference, and distinguishing disk types by the number of times the level of the binary signal changes.
The disks can be correctly distinguished by detecting the number of times the level of the binary signal changes in the focus error search since the number is determined correspondingly to respective disks.
Preferably, the first and second threshold values respectively correspond to those values obtained by multiplying by a prescribed value the maximum value and the minimum value of an output from an optical pickup produced when focus search operation is executed by setting the optical pickup in a compact disk reproduction state.
The output from the pickup obtained by the focus search in the CD reproduction state is smaller than an output from the pickup, for example, obtained by the focus search in a DVD reproduction state. Accordingly, dispersion of detected signals does not seriously affect the distinguishing operation when the pickup output obtained by the focus search in the CD reproduction state is used as a reference. Consequently, a method of distinguishing disks which is not easily subjected to influence of noises can be provided.
According to another aspect of the invention, a disk reproduction apparatus capable of reproduction from a first disk and from a second disk different from the first disk includes an optical pickup that detects a reproduction signal from the first or the second disk. The optical pickup is used to execute focus operation selectively in a first reproduction state suitable for reproduction from the first disk and in a second reproduction state suitable for reproduction from the second disk. The disk reproduction apparatus includes a detector detecting a first difference between the maximum value and the minimum value of an output from the optical pickup obtained by the focus operation in the first reproduction state as well as a second difference between the maximum value and the minimum value of an output from the optical pickup obtained by the focus operation in the second reproduction state, an arithmetic unit calculating a ratio between the first difference and the second difference, a comparator comparing the calculated ratio with a prescribed value, and a controller controlling the reproduction apparatus to accomplish reproduction suitable for the first or the second disk based on the result of the comparison by the comparator.
Using the optical pickup, focus operation is executed for the first or the second disk selectively in the first reproduction state suitable for reproduction from the first disk or in the second reproduction state suitable for reproduction from the second disk, the ratio between the differences between the maximum values and the minimum values of respective outputs obtained in the focus operation in the first and second reproduction states is calculated, and based on the calculated
Hogan & Hartson LLP
Sanyo Electric Co,. Ltd.
Tran Thang V.
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