Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-05-31
2004-08-17
Young, W. R. (Department: 2652)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053220, C369S112240
Reexamination Certificate
active
06778472
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup apparatus used in an optical head apparatus or an optical disk apparatus for recording or reproducing data to or from an optical recording medium such as, for example, an optical disk or a magneto-optical disk.
2. Description of the Related Art
Conventionally, an optical recording medium or a disk is used for storing video and audio information or computer data. In recent years, there has been a strong demand for a higher density and larger capacity optical recording medium.
The recording density of a recording medium can be improved by, for example, increasing a numerical aperture (hereinafter, referred to as an “NA”) of an objective lens provided in the optical pickup apparatus or shortening the wavelength of light emitted by a laser device provided as a light source. However, increasing the NA of the objective lens requires a distance from the objective lens to the recording medium to be reduced. The objective lens having a high NA has larger aberration than an objective lens having a low NA. The aberration is caused by a tilt of the recording medium with respect to the objective lens. Under such circumstances, there has been proposed a method of reducing the thickness of a glass cover of the recording medium so as to reduce the aberration, so that recording or reproduction of data to or from such a recording medium is performed using an objective lens having a high NA and light having a shorter wavelength.
However, it is difficult to reproduce information from conventional CDs, DVDs or other types of disks using an objective lens having a high NA since the conventional disks are designed to have data stored thereon reproduced using an objective lens having a low NA. Accordingly, in order to reproduce data stored on the conventional CDs or DVDs in an optical pickup apparatus designed for a high-density, large-capacity disks, the optical pickup apparatus needs to include an objective lens having a low NA for the conventional CDs or DVDs in addition to an objective lens having a high NA.
FIG. 14
shows an optical pickup apparatus
300
disclosed in Japanese Laid-Open Publication No. 11-120587. The optical pickup apparatus
300
includes a holder
55
. The holder
55
accommodates a first optical system
52
having a high NA including a first objective lens
50
and a second objective lens
51
, and a second optic system having a low NA, i.e., a third objective lens
53
(the second optical system will sometimes be indicated by reference numeral “
53
” for the sake of convenience). The first optical system
52
is provided for recording or reproducing data to or from a first disk
71
, and the second optical system
53
is provided for recording or reproducing data to or from a second disk
70
. The optical pickup apparatus
300
uses the first optical system
52
or the second optical system
53
in accordance with which of the disk
70
or
71
is used. Since the first optical system
52
and the second optical system
53
have different NAs from each other, the first objective lens
50
and the third objective lens
53
are located so as to be away from the first disk
71
and from the second disk
70
by different distances.
The conventional optical pickup apparatus
300
having such a structure involves the following problems.
(1) The difference between the distance from the first objective lens
50
to the first disk
71
and the distance from the third objective lens
53
to the second disk
70
are adjusted to be set distances, respectively, by the position of the holder
55
. Accordingly, when the second optical system having a low NA (i.e., the third objective lens
53
) becomes uncontrollable in the direction of an optical axis thereof while the second disk
70
is being used for recording or reproduction (i.e., the second optical system
53
is used), the first optical system
52
may possibly collide against the second disk
70
resulting in the second disk
70
or the fist optical system
52
being damaged.
(2) In the case where the third objective lens
53
(i.e., the second optical system having a low NA) and the first objective lens
50
included in the first optical system
52
having a high NA are located on substantially the same plane, the following problems occur. The distance between the first disk
71
and the first optical system
52
which is required to record or reproduce data to or from the first disk
71
is significantly different from the distance between the second disk
70
and the second optical system
53
which is required to record or reproduce data to or from the second disk
70
. Therefore, when the first optical system
52
is switched to the second optical system
53
or vice versa, the holder
55
needs to be moved a distance which is too far to guarantee an appropriate tilt of the disk with respect to the respective objective lens.
“(3) In the above-described case, a DC current needs to be continuously supplied to the holder
55
in order to move the holder
55
to a prescribed position to obtain the required distance from the optical system and the objective lens. This increases the power consumption.”
SUMMARY OF THE INVENTION
An optical pickup apparatus according to the present invention includes a first optical system for recording or reproducing signals to or from a first optical recording medium; a second optical system for recording or reproducing signals to or from a second optical recording medium; a holder for accommodating the first optical system and the second optical system on substantially the same plane; a focusing driving device for moving the holder in a first direction parallel to an optical axis of the first optical system and the second optical system; a tracking driving device for rotating the holder in a second direction perpendicular to the optical axis of the first optical system and the second optical system; a switching device for placing the first optical system on an optical path for recording or reproducing signals to or from the first optical recording medium, and for placing the second optical system on the optical path for recording or reproducing signals to or from the second optical recording medium, and a variable distance driving device for varying a distance between the first optical recording medium and the first optical system from a distance between the second optical recording medium and the second optical system when one of the first optical system and the second optical system is switched to the other optical system.
In one embodiment of the invention, the variable distance driving device drives the holder in a direction of the optical axis.
In one embodiment of the invention, the variable distance driving device drives the holder in the direction of the optical axis by a magnetic repulsive force.
In one embodiment of the invention, the variable distance driving device drives the holder in the direction of the optical axis by the magnetic repulsive force when the holder is not moving in the second direction or when one of the first optical system and the second optical system is switched to the other optical system.
In one embodiment of the invention, the variable distance driving device drives the holder in the direction of the optical axis by a magnetic attractive force.
In one embodiment of the invention, the variable distance driving device drives the holder in the direction of the optical axis by the magnetic attractive force when the holder is not moving in the second direction or when one of the first optical system and the second optical system is switched to the other optical system.
In one embodiment of the invention, the variable distance driving device moves the holder when the first optical recording medium or the second optical recording medium is mounted on the optical disk apparatus such that a distance from the recording medium to the holder is larger than a prescribed distance from the second recording medium to the holder when the second optical system is located in th
Agustin Peter Vincent
Conlin David G.
Tucker David A.
Young W. R.
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