Dynamic information storage or retrieval – Information location or remote operator actuated control – Selective addressing of storage medium
Reexamination Certificate
2001-09-20
2004-06-01
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Information location or remote operator actuated control
Selective addressing of storage medium
C369S030150
Reexamination Certificate
active
06744702
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-301472, filed Sep. 29, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a disk apparatus for performing recording/reproduction on a disk having information recording tracks, more specifically, it relates to a method of access control of a disk apparatus that performs positioning on a target track with use of two actuators: coarse and precise actuators.
In the field of optical disks, represented by DVDS, a disk having a diameter of 120 mm and a recording capacity of 4.7 GB has been brought into practical use in recent years. It is also expected that a disk having a recording capacity 3-4 times larger than that of this disk will be developed for practical use several years later. In order to cope with the increase in the recording density in the disk due to the increase in the recording capacity, more specifically, with the reduction of a track pitch, the servo precision having more precise positioning performance is now required for a disk recording/reproducing drive.
In fact, the highly precise positioning technique is essential for an optical disk apparatus to realize positioning of an optical spot in the direction of the diameter of a disk in the order of several nm on information recording tracks each having a pitch of 1 &mgr;m or less. On the other hand, the access speed is also an important factor of the performance of the disk drive. A disk apparatus thus needs an access control technique capable of positioning, satisfying both the demands of high-speed and high precision.
Generally, in order to cover the diameter of a disk and realize highly precise positioning, the positioning of the optical spot is performed with two actuators, i.e., coarse and precise actuators. Access control, using these two actuators, in order to realize the access with high-speed and high precision, will now be described.
These two actuators, however, have some limitations.
The limitation of the precise actuator is that in displacement amount. In accordance with the increase of the optical disk in density, the requirements of the specification of optical elements used for the optical disk apparatus are becoming stricter. For example, the shift of an objective lens from the optical axis is required to be 50 &mgr;m or less for a 4.7 GB DVD disk. If the shift is larger, the optical aberration becomes larger, and the recording/reproduction of information or detection of a positioning signal is adversely affected. A biaxial actuator is used as a precise actuator for positioning an objective lens, and has a limitation in the displacement amount.
The limitation of the coarse actuator is poor positioning precision. The coarse actuator is intended to coarsely position the objective lens in the direction of the radius of a disk. To cope with the requirement for reduction of manufacturing cost, the coarse actuator is formed of low-cost components: a sliding bearing and a low-cost positioning motor. Similarly, a driving force transmission mechanism is subject to many non-linear factors, such as friction and backlash. The positioning precision of the coarse actuator is as poor as 100 &mgr;m.
It is now required for the optical disk apparatus to perform the positioning satisfying both high-speed and high precision with use of the two actuators without large displacement of the precise actuator. Some access control methods have been proposed to overcome the above-mentioned limitations by suitably making the two actuators cooperate with each other.
The conventional access control methods by the cooperation of the precise and coarse actuators will be described below in conjunction with the block diagrams of
FIGS. 2 and 8
. The constitution shown in these diagrams comprises a feed motor (a coarse actuator)
107
for moving an optical head
103
, and an objective lens actuator (a precise actuator)
106
for positioning only an objective lens
102
, in order to position the optical spot on a disk
101
.
The access control according to the above-mentioned apparatus is performed with use of reflected light from the disk
101
after canceling the tracking control shown in FIG.
8
.
In the tracking state, a track traversing signal generated when the optical spot traverses a track on the disk
101
is detected by a light detector
105
and a comparison processing circuit
108
. The track traversing signal is input into a precise positioning mechanism controlling compensator
402
and then input into a precise positioning mechanism
106
via an amplifier
13
and a precise positioning mechanism driving circuit
15
. The precise positioning mechanism
106
is controlled so as to move the optical spot to the same track. The track traversing signal is also supplied to a coarse positioning mechanism controlling compensator
403
and then input into a coarse positioning mechanism
107
via an amplifier
16
and a coarse positioning mechanism driving circuit
19
. Similarly to the precise positioning mechanism
106
, the coarse positioning mechanism
107
is controlled so as to move the optical spot to the same track.
Simultaneously to the staring the access, the tracking state is switched to the control state controlled by the control system constituted as shown in the block diagram of FIG.
2
. In the access control by the control system, the light detector
105
detects the track traversing signal (the tracking error signal). A counter
110
counts the number of traversed tracks on the basis of the track traversing signal. A reference speed generator
111
generates a target speed (a reference speed) based on the number of the remaining tracks.
On the other hand, a speed detector
114
binarizes the track traversing signal to generate a track count pulse, then divides a track pitch by an interval of the track count pulses to obtain a relative moving speed on the tracks. A gain compensator
113
compensates the difference between the relative moving speed and the reference speed by amplification to output a drive signal to the feed motor
107
as the coarse actuator.
According to the conventional method, the access control by the speed control is performed at first, wherein the difference between the relative moving speed and the reference speed is fed back to the feed motor
107
until the detected relative moving speed equals the reference speed. It is found that the detected relative moving speed equals the reference speed when the output of the gain compensator
113
, which indicates the difference thereof, becomes 0. When the detected relative moving speed equals the reference speed, a control circuit
119
switches Sw
1
and Sw
2
.
After switching Sw
1
and Sw
2
, the objective lens actuator
106
is controlled by the difference between the relative moving speed and the reference speed, and the feed motor
107
is controlled by the output from a displacement sensor
104
for detecting the amount of shift of the objective lens
102
from the optical axis.
The objective lens actuator
106
is subjected to the speed control, and the feed motor
107
is controlled so as to move in accordance with the displacement of the objective lens
102
. Such a control system is constituted to perform acceleration with the maximum capacity in high-speed access in order to shorten the access time, and in low-speed access, to control the coarse and precise actuators so as to cooperate for attaining the precise access.
The above-mentioned constitution, however, essentially needs an expensive sensor for actually detecting the relative displacement of the objective lens, and thus the reduction in the manufacturing cost cannot be attained. In addition, the feed motor and the driving force transmission mechanism is subject to non-linear factors and delay factors such as friction, as described above, and it thus may frequently occur that the displacement of the actuator may not actually attained with use
Dinh Tan
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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