Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2001-03-22
2003-11-04
Psitos, Aristotelis M (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S044130, C369S053310
Reexamination Certificate
active
06643239
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to methods and devices for recording information on an optical disk based on a mark-length recording scheme, where pits are formed sequentially from the inner circumference to the outer via a light beam irradiated onto a track in the form of a groove or land running on the disk's recording surface. More particularly, the present invention relates to an improved optical disk recording method and device which can form pits accurately on and along the center line of the optical disk track.
The present invention also relates to servo-balance adjusting methods and servo-balance detecting devices for optical disk recording and optical disk recording devices which are directed to achieving enhanced recording signal quality by optimizing servo balance in focus servo, tracking servo and the like for recording on an optical disk. More particularly, this invention relates to a technique for readily adjusting the servo balance with high accuracy.
In write-once optical disks such as CD-R (CD-Recordable) and DVD-R (DVD-Recordable) as well as rewritable optical disks such as CD-RW (CD-Rewritable), DVD-RAM and MO (Magneto Optical disk), guide grooves commonly called “grooves” or “pre-grooves” are previously formed. Pits are formed sequentially in a track in the form of such a groove or land (a portion between adjoining grooves) by irradiating a laser light beam onto the rotating disk along the track. In recording on such optical disks, tracking control to allow the laser light beam along the track has been performed conventionally in such a way that the center of the optical axis of the laser light beam strikes the center line of the track when a tracking error signal is at a zero level.
Experiments conducted by the inventor of the present invention have shown that, in high-speed recording such as at six-times (i. e., six times faster than the normal speed), eight-times or higher speed as well as in high-density recording with a track pitch (spacing between adjoining tracks) narrower than the normal pitch, pits tend to be formed off the center line of the track even when the laser light beam is irradiated with the center of its optical axis accurately positioned at the track center line, as explained below in relation to FIG.
2
.
In
FIG. 2
, there is shown a write-once optical disk
10
having a dye layer, where a transparent substrate
12
has grooves
14
previously formed therein and running helically around the central axis of the disk
10
. Lands
16
are formed between adjoining grooves
14
. The dye layer
18
functioning as a recording layer is formed on or films the transparent substrate
12
, and reflective, protective and other layers (not shown for simplicity of illustration) are laminated on the dye layer
18
. To record information on the optical disk
10
, laser light
20
, whose intensity is modulated by a recording signal, is converged via an objective lens
22
and passes through the transparent substrate
12
onto the track (groove
14
in this example), to thereby form a pit
24
therein. At that time, the tracking control is performed so as to allow the center
26
of the optical axis of the laser light beam
20
to be positioned on the center line of the track.
However, if high-speed or high-density recording is effected with such conventional tracking control, the pit
24
tends to be formed off the track center line
28
of the track T toward the inner circumference of the disk, due to the influence of residual heat from an adjoining track T′, located inward of the currently recorded track T, where recording has taken place immediately before the current recording. This positional deviation of the pit formed would lead to various inconveniences such as deterioration of the recording sensitivity and reproduced signal quality. Degree of the pit's positional deviation varies depending on the type of the disk used (such as the material used for the recording layer and the track pitch) and the recording speed (linear velocity of the disk as well as a selected “recording speed magnification”).
Further, in such optical disk recording, focus servo and tracking servo are each implemented by first determining a servo error through predetermined arithmetic operations between reflected light reception signals representative of a reflection of the recording laser light beam from the optical disk and then driving a servo actuator to minimize the error. In the predetermined arithmetic operations, servo-balance adjustment is made which is intended to adjust the levels of the reflected light reception signals relative to each other. The servo balance needs to be adjusted with high accuracy, because the quality and characteristics (such as a jitter characteristic) of recording signals are greatly affected depending on how the servo balance is adjusted.
FIG. 13
is explanatory of the servo balance adjustment employed in the conventional focus servo and tracking servo control (the focus servo balance adjustment is for changing the depth of the light beam focus), and more particularly showing an HF (High Frequency) signal waveform corresponding to the reflected light reception signals that represent the light beam reflection from the optical disk during recording. The HF signal waveform would present, in its falling phase, a different downward curve depending on the servo balance setting, and the sharpest downward curve generally represents an optimum servo balance setting. Thus, in plants manufacturing optical disk recording devices, it has been conventional for human operators to detect when a sharpest downward curve of the HF signal waveform appears on an oscilloscope while manipulating focus-servo-balance and tracking-servo-balance adjusting variable resistors, and fix these variable resistors at positions where the sharpest downward slope could be obtained.
However, with such conventionally servo balance adjustment, it was difficult to visually determine the sharpest downward curve of the HF signal waveform, so that the servo balance adjustment values would considerably vary depending on the human operator in charge and servo balance adjustment could not be made optimally. Automatization of the servo balance adjustment was also difficult to realize with the conventional approach. Further, an optimum focus servo balance providing an optimum focus depth of the laser beam light was not easy to achieve, since the kind and film thickness of the dye vary depending on the type of the optical disk. Similarly, an optimum tracking servo balance varies depending on the type of the optical disk. In addition, because the servo balance adjustment was already completed and fixed prior to shipment of the recording devices from the plants, the servo balance could not be adjusted freely by users depending on the type of a disk they want to use.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide an optical disk recording method and device which can form pits accurately centered on the center line of a recording track.
It is a second object of the present invention to provide a servo-balance adjusting method and servo-balance detecting device for optical disk recording and an optical disk recording device which can readily adjust servo balance with high accuracy and also permit adjustment of the servo balance in actual use by users.
According to an aspect of the present invention, there is provided an optical disk recording method for recording information on an optical disk, based on a mark-length recording scheme, by forming pits sequentially from an inner circumference to an outer circumference of the optical disk via a light beam irradiated onto a track formed as a groove or land on a recording surface of the optical disk, and this optical disk recording method is characterized in that tracking control is performed in such a way that a center of an optical axis of the light beam is offset, by a predetermined amount, from a center line of the track toward the outer circumfere
Pillsbury & Winthrop LLP
Psitos Aristotelis M
Yamaha Corporation
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