Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Of record carrier
Reexamination Certificate
1999-03-25
2001-08-07
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Of record carrier
C369S044130, C369S047100
Reexamination Certificate
active
06272089
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pre-pit detecting apparatus for detecting a pre-pit signal, which carries pre-pit information such as address information and which is recorded in advance on an optical disc on which record information of video data, audio data and the like can be recorded later by a user.
2. Description of the Related Art
There is a CD-R (Compact Disc Recordable) as a WO (Write-Once) type of high density recording medium, onto which the record information data can be written just once. The CD-R is an optical record medium having a record capacity similar to that of a CD dedicated to a reproduction. Pre-information, such as address information required to search a position on the optical disc at which the record information is to be recorded, rotation control information used for a rotation control of the CD-R, such as a synchronization signal, are recorded by wobbling an information record track (i.e., a groove track or a land track) on which the record information is to be recorded, in a wave form based on a signal which is FM (Frequency Modulation)-modulated in accordance with the pre-information to be recorded, at the stage of pre-formatting when the CD-R is manufactured.
When the information is actually recorded onto the CD-R, a signal including a wobbling frequency component of the wobbled track (hereafter, referred to as a wobbling signal) is detected, and a standard clock for controlling the rotation of the CD-R is extracted therefrom. Then, a drive signal for controlling a rotation of a spindle motor of rotating the CD-R is generated on the basis of the extracted standard clock. Also, a clock signal for the recording operation is generated which includes the information of a timing synchronous with the rotation of the CD-R.
Moreover, the address information on the CD-R required to record the record information is obtained from the wobbling signal. A position at which the record information is to be recorded is detected in accordance with the obtained address information to thereby record the record information.
There is a DVD-R (DVD-Recordable) in which the record density is improved over the CD-R. In this DVD-R, an interval between the information record tracks adjacent to each other is substantially half of that of the CD-R, from a request of improving the record density. Thus, even if the pre-information is obtained from the conventionally-wobbled information record track on the DVD-R, the wobbling signals on the information record tracks adjacent to each other interfere with each other. Hence, there may be a case that the wobbling signal cannot be exactly detected.
Then, in a case of the DVD-R, the pre-information is recorded by wobbling the information record track (for example, the groove track) on the DVD-R at a frequency in accordance with the standard clock and additionally forming pre-pits corresponding to the pre-information on a guide track (for example, the land track), which is positioned between the information record tracks adjacent to each other and which guides a light beam to the information record track. Moreover, the pre-pits are substantially uniformly formed on an entire surface of the DVD-R so that the standard clock can be generated from the pre-pits as the occasion demands.
The pre-information is obtained by detecting such a pre-pit, and the exact rotation control and the record control are carried out in accordance with this pre-information.
By the way, the applicant knows one method of detecting the pre-pit, which is carried out as follows.
That is, as shown in
FIG. 10
, a gate signal, which is phase-synchronous with the wobbling signal obtained by emitting a light beam onto the information record track, is generated. Then, only the signal exceeding a predetermined threshold signal is extracted by comparing the wobbling signal with the predetermined threshold signal.
Then, the pre-pit signal superimposed on the wobbling signal is extracted by calculating a logical product of this extracted signal and the gate signal.
However, if a defect resulting from a crack, a dust and the like is present on the DVD-R, there may be a case that this defect causes a noise in a form of a pulse, which is superimposed on the wobbling signal. In such a case, the pre-pit detecting apparatus using the above-mentioned method of detecting the pre-pit may erroneously detect the noise in the form of the pulse as the pre-pit signal.
SUMMARY OF THE INVENTION
The present invention is proposed in view of the above mentioned problems. It is therefore an object of the present invention to provide a pre-pit detecting apparatus, which can reduce the an erroneous detection of a pre-pit signal even if a noise component in a form of a pulse is superimposed on a wobbling signal because of a defect on a disc.
The above object of the present invention can be achieved by a first pre-pit detecting apparatus for detecting a pre-pit signal based on a pre-pit from an optical disc, on which an information record track wobbled in accordance with a wobbling signal is formed and on which pre-pits are formed at an predetermined interval on a guide track adjacent to the information record track. The first pre-pit detecting apparatus is provided with: a composite signal extracting device for extracting a composite signal, in which the pre-pit signal is superimposed on the wobbling signal, out of a reflection light from the optical disc; a relaying device for relaying the composite signal extracted by the composite signal extracting device; a pre-pit signal detecting device for detecting a component of the pre-pit signal from the composite signal relayed by the relaying device; a wobbling signal extracting device for extracting a component of the wobbling signal out of the composite signal relayed by the relaying device; a synchronization wobbling signal generating device for generating a synchronization wobbling signal, whose frequency and phase are respectively synchronous with a frequency and a phase of the wobbling signal extracted by the wobbling signal extracting device; and a defect detecting device for detecting a defect on the optical disc, the relaying device relaying the synchronization wobbling signal instead of the composite signal, if the defect is detected by the defect detecting device.
According to the first pre-pit detecting apparatus, when a light beam is emitted onto the optical disc and the reflection light of the light beam is received from the optical disc, the composite signal, in which the pre-pit signal is superimposed on the wobbling signal, is extracted out of the reflection light by the composite signal extracting device. Then, the extracted composite signal extracted is relayed by the relaying device. Then, the component of the pre-pit signal is detected by the pre-pit signal detecting device, from the relayed composite signal. On the other hand, the component of the wobbling signal is extracted by the wobbling signal extracting device out of the relayed composite signal. The synchronization wobbling signal, whose frequency and phase are respectively synchronous with the frequency and the phase of the extracted wobbling signal, is generated by the synchronization wobbling signal generating device. The defect on the optical disc, onto which a light beam is emitted, is detected by the defect detecting device. At this time, if the defect is detected by the defect detecting device, the synchronization wobbling signal is relayed by the relaying device instead of the composite signal.
Therefore, since the synchronization wobbling signal which is free from the influence of the defect is supplied instead of the composite signal to the pre-pit signal detecting device if the defect is detected, it is possible to prevent the pre-pit signal detecting device from erroneously detecting the noise due to the defect as the pre-pit signal.
The above object of the present invention can be also achieved by a second pre-pit detecting apparatus for detecting a pre-pit signal based on a pre-pit from an optical di
Edun Muhammad
Pioneer Electronic Corporation
Pitney Hardin Kipp & Szuch LLP
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