Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-01-28
2002-04-09
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044270, C369S094000
Reexamination Certificate
active
06370093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to optical disk devices and, more particularly, to optical disk devices reproducing or recording information from multilayered optical disks having a plurality of signal recording layers.
2. Description of the Related Art
While a typical compact disk (CD) or a typical Compact Disk-Read Only Memory (CD-ROM) available at the present has a recording capacity of 640M bytes, a digital video disk (DVD) with a recording capacity of 4.7 Gbytes is also available with the recent increase in the density. A CD or CD-ROM has a thickness of 1.2 mm and a diameter of 12 cm. A DVD has half the thickness of a CD or CD-ROM, i.e. 0.6 mm, and has the same diameter that a CD or CD-ROM, i.e. 12 cm. There has also been proposed a dual layer DVD having its signal recording surface double-layered to obtain a recording capacity of 8.5 Gbytes (see e.g. Toshinori Kishi et al., “Dual-Layer Optical Disc Capable of Reading from a Single Side”, National Technical Report Vol. 41, No. 6, pp. 10-16, December 1995). The method of reproducing information from a dual layer optical disk having two recording layers or signal recording surfaces can include reproducing the information recorded on the two signal recording surfaces from one side of the disk and reproducing the information recorded on the two signal recording surfaces from their respective sides of the disk. The method of reproducing the information recorded on the two signal recording surfaces from their respective sides is, however, cumbersome, because the disk is required to be turned over in initially completing the reproduction of the information on one signal recording surface and then reproducing the information on the other signal recording surface. This method also fails to immediately reproduce the information on one signal recording surface when the information on the other signal recording surface is being reproduced. Thus, the technique of reproducing information recorded on two signal recording surfaces from one side of the disk is the mainstream of reproducing the information thereon.
As shown in
FIG. 59
, a one-side reading, dual layer optical disk has a reflective recording layer
1
formed of e.g. aluminum and having a reflectance of at least 70% and a translucent recording layer
2
formed, e.g., of gold and having a reflectance of approximately 30% and the two recording layers
1
,
2
sandwich ultraviolet-ray hardened resin of approximately 40 &mgr;m in thickness as an intermediate layer
3
. On reflective recording layer
1
and translucent recording layer
2
is recorded such information as shown in FIG.
60
. More specifically, the information includes data and ID. The ID includes address (track No.), layer information (layer number), and track information (track format information, area information, track system, reflectance).
Because the dual layer optical disk has one recording surface that is translucent, a laser beam can be radiated from one side of the disk and focused on each recording layer to read the information recorded on the recording layer via an optical pickup device.
Furthermore, for a dual layer optical disk, the so-called focus jump (see e.g. Japanese Patent Laying-Open No.8-171731) is provided. More specifically, when the information on one recording layer is being reproduced an objective lens is moved in the direction of the optical axis so that the laser beam is refocused on the other recording layer to start reproduction of the information on the other recording surface.
The conventional focus jumping, however, has a disadvantage that access time is increased, because a targeted address is sought for after focus-jumping is performed.
Furthermore, the distance between the two layers of a dual layer optical disk is, in fact, not uniform over the entirety of the disk, varying in the radial direction. Thus, it is difficult to provide accurate focus-jumping at any location of the dual layer optical disk.
Furthermore, the conventional focus-jumping depends on the mechanical technique of employing an actuator for focusing servo control to move an objective lens in the direction of the optical axis. Thus, a long period of time is required to move the focal point of a laser beam from one recording layer to the other recording layer. There is also a problem that the conventional device often breaks down.
There is also a problem that if there is a pinhole or the like in a recording surface of a DVD, the layer information of an address is not clearly obtained and the layer of interest cannot be determined.
Furthermore, if the disk is damaged or suffers from surface aberration, a focusing error signal is not detected from its reflecting surface. Thus, the object lens will not be decelerated and disadvantageously collide with a surface of the disk.
One object of the present invention is to provide an optical disk device capable of accurate focus-jumping.
Another object of the present invention is to provide an optical disk device capable of reducing the time required for seeking a targeted address.
Still another object of the present invention is to provide an optical disk device capable of accurate focus-jumping at any location within a multilayer optical disk.
Still another object of the present invention is to provide an optical disk device capable of rapid focus-jumping.
Still another object of the present invention is to provide an optical disk device capable of identify each layer if a signal recording surface is damaged.
Still another object of the present invention is to provide an optical disk device capable of preventing an optical lens from colliding with a surface of an optical disk in focus-jumping.
SUMMARY OF THE INVENTION
According to the present invention, an optical disk device reproducing the information from an optical disk having the information recorded on a signal recording surface of a plurality of layers includes information reading means illuminating an optical disk with a beam via an objective lens and detecting a light reflected from the optical disk to read information, acceleration means producing and providing to the information reading means an acceleration signal for accelerating the objective lens in the direction of a normal to a signal recording surface of one of the plurality of layers to focus the beam on the signal recording surface of one layer when the information reading means is focusing the beam on a signal recording surface of another layer of the plurality of layers, and deceleration means producing and providing to the information reading means a deceleration signal for decelerating the objective lens when a focusing error signal obtained from the information reading means attains a predetermined level.
Preferably, the predetermined level is provided between the 0 level and peak level of the focusing error signal. The voltage of the deceleration signal is predetermined depending on the time taken from the generation of the acceleration signal by the acceleration means until the focusing error signal attains the predetermined level.
Preferably, the predetermined level is provided between the 0 level and peak level of the focusing error signal. Deceleration signal supply time is predetermined depending on the time taken from the generation of the acceleration signal by the acceleration means until the focusing error signal attains the predetermined level.
Preferably the deceleration means decreases the voltage of the deceleration signal stepwise.
Preferably the optical disk device also includes differentiation means differentiating the focusing error signal. The deceleration means varies the voltage of the deceleration signal depending on the maximal value of the focusing error signal differentiated.
Preferably, the optical disk device also includes storage means storing a plurality of predetermined levels of voltage of the deceleration signal corresponding to a plurality of maximal values of the focusing error signal differentiated, and reading means responsive to a maximal value of the differentiated f
Hirose Ken
Ichiura Shuichi
Ohe Shinichi
Tada Koichi
Takagi Naoyuki
Armstrong Westerman & Hattori, LLP
Sanyo Electric Co. Ltd
Tran Thang V.
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