Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-02-14
2003-09-16
To, Doris H. (Department: 2655)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044230, C369S044290, C369S044370, C369S244100
Reexamination Certificate
active
06621771
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to disk drives including optical heads for use with optical disks of different specifications. In particular, the invention relates to a disk drive having an optical head disposed in a position in which tracking can be corrected.
2. Description of the Related Art
Disk drives which can read to and write from media such as compact disks (herein referred to as CD) and digital versatile disks (herein referred to as DVD) are known, which are used as devices such as peripheral devices of computers. Various types of disk drives are widely used for read-only media such as CD-ROM and DVD-ROM, and for read-and-write media such as CD-R, CD-RW, and DVD-R. Optical disks used in such disk drives have substantially the same inner and outer diameters.
In a known disk drive, an optical head is used for reading data, and tracking correction servo and focus correction servo are performed while a center of an objective lens provided in the optical head moves along a radial line of a disk. The tracking correction servo is performed by slightly moving the lens along a direction parallel to the surface of the disk, and the focus correction servo is performed by slightly moving the lens along a direction perpendicular to the surface of the disk.
A disk drive which is commonly used for different types of media such as CD and DVD must be provided with optical heads corresponding to each of the media, as the media have different structural specifications, etc.
A known disk drive of the above-described type is disclosed, for example, in Japanese Unexamined Patent Application Publication Nos. 9-17156 and 9-17157 (herein referred to as (A)), in which different optical pickups (optical heads) are provided in positions symmetrical with respect to the center of rotation of the disk, the center of each of the optical pickups moving along a radial line of the disk.
Another known disk drive is disclosed in Japanese Unexamined Patent Application Publication Nos. 9-17155 and 10-21570 (herein referred to as (B)), in which a plurality of optical heads (optical pickups) of different specifications are disposed adjacent to each other, and their positions are selectively changed so that a center of an objective lens of the selected optical head can move along a radial line of the disk.
In the disk drive, tracking correction servo is performed in which a tracking error signal is detected by laser beams applied to the disk, wherein the objective lens must be moved along a radial line of the disk, as described in (A) and (B) above.
In the disk drive disclosed in (A) above, a problem has been found in that the design options are limited because the optical heads must be disposed at both sides of the center of rotation of the disk, and spaces are required for the movement of each optical head, the optical heads being disposed so that centers of objective lenses thereof can move along radial lines of the disk. Regarding miniaturization, the disk drive disclosed in (B) above is superior to the disk drive described in (A) above. However, the problem is that the structure and the circuitry of the optical heads are complex because a mechanism for selectively changing the objective lenses must be provided, and the overall cost may be high due to the development cost of optical system of both optical heads.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a disk drive in which an optical head can be disposed free from the design restriction that a center of an objective lens must move only along a radial line of the disk.
According to an aspect of the present invention, a disk drive is provided which comprises a rotational-driving mechanism for rotating a disk; an optical head including a tracking correction mechanism for slightly driving an objective lens along a direction crossing recording tracks on the disk; and an optical head transferring mechanism for transferring the optical head in a manner such that the optical axis of the objective lens moves along a transfer line separated by a distance L from a reference radial line extending from the center of rotation of the disk rotated by the rotational-driving mechanism, the transfer line being parallel to the reference radial line. In the disk drive, the distance L and the tracking correction direction of the objective lens driven by the tracking correction mechanism are set so that an expression R
0
<(Rmin+Rmax)/2 is satisfied, in which Rmin represents a distance between the center of rotation of the disk and the optical axis of the objective lens, the distance being reduced to a distance along the reference radial line, when the objective lens is positioned on the innermost track of the disk, Rmax represents a distance between the center of rotation of the disk and the optical axis of the objective lens, the distance being reduced to a distance along the reference radial line, when the objective lens is positioned on the outermost track of the disk, and R
0
represents a distance between the center of rotation of the disk and the optical axis of the objective lens, the distance being reduced to a distance along the reference radial line, when the objective lens is positioned on a track between the innermost track and the outermost track. The tracking correction direction is a direction of the radial line between the optical axis of the objective lens and the center of rotation of the disk.
According to the present invention, tracking servo is enabled in an optical head in which the optical axis of the objective lens does not move along a radial line of the disk, and the effect of offset is minimized by computing and setting the distance L and the tracking correction direction to satisfy the expression above. The optical head is not necessarily designed so that the optical axis of the objective lens moves along a radial line of the disk. The structure of the optical head is not complex because mechanisms for selectively changing optical heads are not required, thereby lowering the manufacturing cost.
When optical heads to be applied to two disks of different types of specifications are movably provided for reading from the two disks, an objective lens of a first optical head is disposed so that the optical axis thereof moves along a radial line of the disk between the innermost track and the outermost track, and an objective lens of a second optical head is disposed so that the second optical head is inclined toward the center of rotation of the disk with respect to the radial line of the disk. The optical axis of the objective lens of the second optical head moves along a line separated by a predetermined distance from the optical axis of the objective lens of the first optical head, in parallel to a line along which the optical axis of the objective lens of the first optical head moves, the objective lens of the second optical head moving between the innermost track and the outermost track. In this case, the line along which the optical axis of the objective lens of the first optical head moves is referred to as a reference radial line.
According to the invention, only the second optical head described above may be provided in the disk drive. In the second optical head, the optical axis of the objective lens thereof is not necessarily transferred along the reference radial line, whereby flexible design options are ensured, and a controlling operation is not required for applying the optical axis of the objective lens to the reference radial line.
The distance between the center of rotation of the disk and the optical axis of the objective lens of the second optical head, which is disposed to be inclined, is reduced to a distance along a direction parallel to the reference radial line from the center of rotation of the disk. That is, the distance on the optical axis is indicated as a distance between the center of rotation of the disk and an intersection of the reference radial line with a perpendicular thereto from the optical axis of the secon
Furuta Kenji
Kyoya Shoichi
Yamashita Tatsumaro
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Patel Gautam R.
To Doris H.
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