Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-05-29
2001-09-04
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044370, C369S053370, C369S053450
Reexamination Certificate
active
06285635
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk apparatus for optically recording signals to an information carrier and reproducing the recorded signals by using light beams from light sources, such as lasers.
2. Related Art of the Invention
Optical disk apparatuses for playing back CD audio and CD-ROM usually use a laser light source with a wavelength of 780 nm.
However, a laser light source with a wavelength of 650 nm is used for high-density optical discs (disks having higher density and larger capacity than CD, and simply referred to as SD).
An apparatus has been proposed, which is provided with a laser with a longer wavelength of 780 nm for CD, and a laser with a shorter wavelength of 650 nm for high-density disks, whereby the laser with the longer wavelength of 780 nm is used to play back CD and CD-R, and the laser with the shorter wavelength of 650 nm is used to play back the high-density disk, SD.
PROBLEMS THAT THE INVENTION IS TO SOLVE
In such an apparatus, it is unknown whether the disk having been loaded in the apparatus is CD or a density disk, SD. To make distinction, each of the two lasers is turned on, and focus servo control and tracking control are carried out, thereby to check whether the disk can be played back or not.
However, in the case that CD-R has been loaded, if laser light with the shorter wavelength is cast, and focus control and tracking servo control are carried out, the light beam from the laser is usually converged and cast to an area ranging from a quarter to a half of one round on the recording film of the disk, thereby causing a problem of erasing recorded information. The erasure of the information is serious to the extent that it cannot be recovered even when error correction is attempted, and the information may not be reproduced. The erasure occurs because of the following reason. Since the organic dye layer of the CD-R has usually been designed to have an optimal reflection characteristic at 780 nm, if laser light with a 650 nm or less is cast, the light is not reflected but absorbed. Therefore, it is difficult to detect the intensity of the reflected light corresponding to information marked on the recording film and to reproduce the information. In addition, the spot of the light beam becomes small and has high power per unit area, and the recording film itself has an absorption characteristic, whereby the recorded information may be erased.
Furthermore, in the case of the above-mentioned conventional optical disk apparatus, when the CD playback speed is increased to 6×, 12× and 24×, the wobbling acceleration and the eccentricity acceleration of the disk increase in proportion to the square of the playback speed (rotation speed) of the disk. As a result, the wobbling acceleration and the eccentricity acceleration may exceed the ranges made allowable by the gains of the focus control and tracking control depending on variations in the disk and variations in the chucking of the disk, whereby control cannot be pulled in, and a problem of disabling start may be caused.
Moreover, it is difficult for the spindle motor to have a constant torque characteristic in the range of high-speed rotation, such as 24×, to low-speed rotation, such as the standard speed. In addition, the spindle motor itself has variations. With these taken into consideration, the rotation control of the disk becomes unstable, and this unstable control causes jitter in reproduced signals, thereby causing a problem of low performance.
SUMMARY OF THE INVENTION
The present invention is intended to solve the problems encountered in the above-mentioned conventional art, and proposes a control method at the start of operation for reproduction (or recording) on CD, CD-R and novel high-density disks. In addition, the present invention also proposes a method of stably pulling in focus control and tracking control, and a method of stably carrying out rotation control, and provides an apparatus for playback and recording on novel high-density optical disks, as well as playback on CD at high performance.
MEANS OF SOLVING THE PROBLEMS
In the present invention, distinction is generally made to determine the type of disk before focus control and tracking control. The converged beam of light thus strikes the recording surface of the disk for a very short time (several milliseconds). Even if one of information marks is lost as a result, the lost mark can be corrected sufficiently, whereby no problem is caused in the reproduction of information.
Furthermore, in an apparatus provided with two or more lasers with longer and shorter wavelengths in accordance with the present invention, for example, in an apparatus provided with three lasers, the light of a laser
1
with the longest wavelength is first cast, and distinction is made to determine whether a loaded disk is CD, CD-R or not in a condition without focus control and tracking control. If the disk is not CD, CD-R, the light of the laser
2
with the second longest wavelength is cast next, and distinction is made to determine whether the loaded disk is a high-density disk or not in the condition without focus control and tracking control in a similar way. If the disk is not a high-density disk, the light of the laser
3
with the shortest wavelength is cast, and distinction is made to determine whether the loaded disk is a super high-density disk or not in the condition without focus control and tracking control in a similar way. The distinction proceeds in this order. When the light of each laser is cast and when the loaded disk is determined to be the type of disk to be played back by using the laser as the result of the distinction, focus control and tracking control are carried out for the first time, whereby binary operation and error correction are carried out, and information on the disk is reproduced.
Furthermore, in the present invention, an apparatus with high reproduction power (reproduction-compatible apparatus for disks, such as CD-RW) is configured to carry out emission at low power during the above-mentioned distinction. Therefore, even if laser light with a shorter wavelength should be cast to a disk, such as CD-R or the like, because of an error in the distinction, information can be prevented completely from being erased.
Next, configurations relating to the present application will be described below.
The first invention of the present configuration is an optical disk apparatus for reproducing information from plural types of information carriers or for recording information to plural types of information carriers, comprising two or more light sources with different wavelengths, a converging means for converging a light beam emitted from each of said light sources on said information carrier, a movement means for moving the converged spot of said light beam converged by said converging means in a direction substantially perpendicular to the surface of said information carrier, a convergence condition detection means for outputting a signal corresponding to the convergence condition of said light beam on said information carrier, an amplitude detection means for measuring the amplitude of said signal of said convergence condition detection means, and a focus control means for driving said movement means in accordance with said output signal of said convergence condition detection means and for performing control so that the convergence condition of said light beam on said information carrier becomes substantially constant, wherein at the start or restart of said apparatus, before said focus control means is driven, when one of said light sources with a predetermined wavelength is turned on, and when said movement means is driven to move said converging means close to and then away from said information carrier or away from and then close to said information carrier, said apparatus makes distinction to determine the type of said loaded information carrier on the basis of a signal from said amplitude detection means; if said light source with
Kishimoto Takashi
Moriya Mitsurou
Watanabe Katsuya
Yamamoto Takeharu
Edun Muhammad
Matsushia Electric Industrial Co., Ltd.
Ratner & Prestia
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