Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-01-04
2003-04-22
Young, W. R. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053140, C369S053280
Reexamination Certificate
active
06552971
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a disk drive apparatus for writing and reading data by emitting laser light onto a signal recording surface of a recording medium having a plurality of signal recording surfaces which form a layered structure.
2. Description of the Related Art
As optical disk recording media, CD-type disks, such as those commonly called “CD-ROMs”, and disks called “DVDs” (Digital Versatile Discs/Digital Video Discs) suitable for multimedia applications have been developed.
In disk drive apparatuses which use these optical disks, data is read by emitting laser light onto tracks on a disk rotated by a spindle motor from an optical pickup and by detecting the reflected light therefrom, or data is written by emitting laser light modulated by writing data onto tracks of a disk.
In order to perform a writing or reading operation by using laser light, the spot of the laser light must be maintained focused on a recording surface of the disk. For this purpose, in the disk drive apparatus, a focusing servo mechanism is provided for controlling the focus by moving an objective lens, which is at the output end of the laser light, toward or away from the disk. This focusing servo mechanism is conventionally formed of a two-axis mechanism having a focusing coil to move the objective lens toward and away from the disk and a tracking coil capable of moving the objective lens in the radial direction of the disk, and formed of focusing servo circuitry for generating a focusing error signal (i.e., a signal indicating the amount of difference from the focused state) from the information in the light reflected from the disk, generating a focusing driving signal in accordance with the focusing error signal, and applying the focus driving signal to the focusing coil of the two-axis mechanism. That is, the focusing servo mechanism is formed as a feedback control system.
Also, as is already well known, the range over which the spot of the laser light is brought into a focused state in accordance with the focusing error signal is in a very narrow range in which an S-shaped curve is observed as a focusing error signal. Consequently, in order to satisfactorily perform focusing servo, generally, an operation called “focusing search” is required as an operation for turning on a focusing servo loop.
In this focusing search operation, a focusing driving signal is applied to a focusing coil so that the objective lens is forced to move within the focusing stroke range thereof. At this time, while the focusing error signal is being detected, when the position of the objective lens is within a particular range, an S-shaped curve is observed. The focusing servo is turned on at the timing (or at the zero-crossing timing) at which the S-shaped curve is linear.
Some types of disks have a plurality of recording surfaces which form a layered structure. For example, in the case of the above-mentioned DVD, two signal recording surfaces, which are generally called “layer
0
” and “layer
1
”, are formed.
The structure of a DVD having two signal recording surfaces is shown in FIG.
14
. The DVD is a disk having a diameter of 12 cm, and the thickness of the disk is 1.2 mm, as shown in FIG.
14
.
In the layered structure of this DVD, first, a disk substrate (transparent layer)
101
of a synthetic resin material, such as a transparent polycarbonate resin, a polychlorinated vinyl resin, or an acrylic resin, having a high light transmittance and mechanical resistance characteristics or chemical resistance characteristics, is formed on a disk surface
108
.
Pits are transferred to the disk substrate
101
by a stamper having a molding die incorporated on one of its main surfaces, forming a first signal recording surface
102
. The pits on this first signal recording surface
102
are formed, as small coded holes whose circumferential lengths differ from each other in accordance with a predetermined information signal, on the disk substrate
101
, forming recording tracks.
Furthermore, a second signal recording surface
104
and a second reflection layer
105
corresponding to the second signal recording surface
104
are formed via a first reflection layer
103
corresponding to the first signal recording surface
102
. The second signal recording surface
104
is also formed with pits corresponding to an information signal in a manner similar to that for the first signal recording surface
102
.
A bonding surface
106
is formed on the second reflection layer
105
, and a dummy plate
107
is bonded via the bonding surface
106
.
Laser light from the disk drive apparatus is made to enter the DVD from the disk surface
108
, and information recorded on the first signal recording surface
102
or the second signal recording surface
104
is detected from the reflected light therefrom.
More specifically, the first reflection layer
103
is formed into a semi-transparent film so that a fixed ratio of laser light is reflected. As a result, if the laser light is focused onto the first signal recording surface
102
, it is possible to read a signal recorded on the first signal recording surface
102
from the light reflected by the first reflection layer
103
. Also, when the laser light is focused on the second signal recording surface
104
, the laser light passes through the first reflection layer
103
and is focused on the second signal recording surface
104
, making it possible to read a signal recorded on the second signal recording surface
104
from the light reflected by the second reflection layer
105
.
For a disk having a plurality of signal recording surfaces, such as a DVD with a two-layered structure, it is necessary for the focusing servo mechanism to focus the laser light onto the respective signal recording surfaces. In other words, when the laser light is focused on one of the signal recording surfaces, it is necessary that an operation for changing the focus onto the other signal recording surface, that is, a focusing jump operation, can be performed.
This focusing jump operation is performed by forcing the objective lens to move while the focusing servo is turned off when a focused state is reached on one of the signal recording surfaces and by turning on the focusing servo when the laser light reaches in a focusing pull-in range for the other signal recording surface (i.e., when the S-shaped curve is observed). That is, this is an operation similar to that in the above-described focusing search operation.
When such a focusing jump is t o be performed, by considering a surface wobbling of the disk, influences of external disturbances are reduced by moving the objective lens at an acceleration larger than the wobbling acceleration thereof.
However, in a disk having a large degree of wobble, the focus position of the objective lens must be displaced greatly within the rotation cycle of the disk. Therefore, in order to perform a focusing jump operation with respect to a disk having a large degree of wobble, it is necessary that complex servo control be performed in which the rotation speed and the amount of wobble of the disk are taken into consideration.
SUMMARY OF THE INVENTION
In order to solve these problems, in one aspect, the present invention provides an apparatus for writing and reading data by emitting laser light on each signal recording surface of a recording medium having a plurality of signal recording surfaces, the apparatus comprising: a pickup device having an objective lens which is at an output end of the laser light; an objective lens moving device for setting the focused state of the laser light with respect to the signal recording surface of the recording medium by moving the objective lens toward or away from the recording medium; a detection device for detecting moved distance information indicating the relative distance moved between the objective lens and the signal recording surface; and a focusing jump control device for controlling the objective lens moving device so that a focusing jump operation is performed for m
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Gautam R.
Sony Corporation
Young W. R.
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