Dynamic information storage or retrieval – Condition indicating – monitoring – or testing
Reexamination Certificate
2000-05-09
2004-04-27
Psitos, Aristotelis M (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
C369S112240
Reexamination Certificate
active
06728179
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical recording/reproducing apparatus which is provided with a mechanism for correcting spherical aberration of a light spot formed by converging light on a data layer of a recording medium by changing a distance between groups of lenses.
BACKGROUND OF THE INVENTION
With respect to the prior art, an explanation will be given of a device disclosed in Japanese Laid-Open Patent Application No. 188301/1998 (Tokukaihei 10-188301, published on Jul. 21, 1998).
FIG. 17
is an explanatory drawing that shows a combination lens in accordance with the conventional technique.
This application discloses a combination lens barrel which changes the combination of lenses and the gap between the combined lenses so that the spherical aberration of a converged light spot on a recording medium is altered.
As illustrated in
FIG. 17
, upon converging light on a recording medium
104
through a combination lens
106
, a first lens
100
is placed on the side of a light source, not shown, and a second lens
101
is placed on the side closer to the recording medium
104
with respect to the first lens
100
. A focus radial actuator (FR actuator)
102
allows the first lens
100
and the second lens
101
to shift in focusing and radial directions. A spherical-aberration correcting actuator
103
drives the second lens
101
to shift in the focusing direction so as to change the gap between the first lens
100
and the second lens
101
, thereby making it possible to correct the spherical aberration of a converged light spot formed on a recording layer
105
of a recording medium
104
.
Light rays, emitted from a light source (not shown), are directed to a combination lens
106
by an optical part (not shown), and converged onto the recording layer
105
of the recording medium
104
.
The reason that the combination lens
106
consisting of a plurality of lenses (first lens
100
, second lens
101
) is provided is because the numerical aperture of the lens is increased, with the result that the use of only one lens makes it difficult to design and manufacture a light-converging system that can converge light efficiently.
When there is an error in the optical thickness from the surface of the recording medium
104
on the combination lens side to the recording layer
105
, a spherical aberration is generated on a light spot converged on the recording layer
105
. Here, since the numerical aperture of the lens is great, the amount of generation of the spherical aberration with respect to the error in the optical thickness from the surface on the combination lens side to the recording layer
105
becomes greater as compared with a lens having a low numerical aperture. For this reason, the gap between lenses is changed so as to reduce the generation of spherical aberration and also to provide an arrangement that is suitable for a recording medium having two or more recording layers.
In this case, the optical thickness refers to a thickness determined by a thickness of a light-transmitting body (or a light-transmitting layer) that transmits light and its refractive index; and even in the case when thicknesses (mechanical thicknesses) are different, if the sizes of spherical aberrations of light spots converged through the respective light-transmitting bodies are coincident, the optical thicknesses of them are assumed to be the same.
Moreover, the error in the optical thickness from the surface of the recording medium on the lens side to the recording layer refers to a difference between an optical thickness of a light-transmitting body (or a light-transmitting layer) that has been assumed at the time of the lens designing and an actual optical thickness from the surface of the recording medium on the combination lens side to each recording layer that is obtained at the time of actually recording/reproducing information on/from the recording medium.
With respect to a driving system for changing the gap between lenses, a system referred to as “voice coil motor” has been proposed, in which: an electromagnetic force is generated by allowing a positive or negative current to flow through a coil so as to generate an electromagnetic force, thereby making the second lens
101
to shift in focussing up and down directions by utilizing a thrust generated between magnets and coils (for example, Japanese Laid-Open Patent Application No. 255290/1998 (Tokukaihei 10-255290, published on Sep. 25, 1998).
Such a spherical-aberration correcting mechanism, which changes the gap between lenses, makes it possible to properly adjust the amount of shift of the second lens
101
, that is, the gap between the first lens
100
and the second lens
101
, so that it becomes possible to correct the spherical aberration generated due to an error in the optical thickness from the recording medium on the combination lens side to the recording layer.
Next, an explanation will be given by exemplifying an invention disclosed in Japanese Laid-Open Patent Application No. 266511/1993 (Tokukaihei 5-266511, published on Oct. 15, 1993).
In
FIG. 18
, a plano-concave lens
107
and a plane-convex lens
108
are placed between an objective lens
109
and a light source (not shown), and the plano-concave lens
107
is shifted in the light axis direction in accordance with the optical thickness of the optical recording medium (corresponding to “the thickness of the protective layer” in Japanese Laid-Open Patent Application No. 266511/1993 (Tokukaihei 5-266511)) so as to correct spherical aberration.
The light, transmitted through the plane-convex lens
108
, is converged on a recording layer
110
a
of an optical recording medium
110
by an objective lens
109
constituted by a plurality of lenses.
In this case, different from the aforementioned example, the spherical aberration is corrected not by the objective lens
109
constituted by a plurality of lenses, but by changing the lens gap of the lenses (plano-concave lens
107
and plane-convex lens
108
) that are placed between the objective lens
109
and the light source.
Moreover, with respect to such a lens driving system, those driven by gears have been disclosed. In other words, a mesh section
111
having a concavo-convex shape formed on the peripheral face of the plano-concave lens
107
and a gear
112
rotatably secured to a shaft are engaged with each other, and the plano-concave lens
107
is driven in the light axis direction by rotating the gear
112
.
Such spherical-aberration correcting mechanisms usually have a system driven electrically; and as compared with the use of a lens having a low numerical aperture, the use of a lens having a high numerical aperture needs high power consumption so as to drive the spherical-aberration correcting mechanism, with the result that a problem of wasteful power consumption arises. Moreover, in the case of the arrangement having a spherical-aberration correcting actuator built in a combination lens barrel, as in the case of the voice coil motor disclosed in Japanese Laid-Open Patent Application No. 255290/1998 (Tokukaihei 10-255290), upon application of a current to a coil, the coil is heated, with the result that parts in the lens barrel are subjected to thermal expansion; this causes variations in the gap, tilt and di-center between the first and second lenses, resulting in a failure in providing an appropriate converged light spot.
SUMMARY OF THE INVENTION
The present invention has been devised to solve the above-mentioned problems, and its objective is to reduce power consumption in a spherical-aberration correcting mechanism for correcting a spherical aberration generated by an error in the optical thickness of a recording medium, and consequently to improve the reliability of the mechanism at the time of recording or reproducing. Moreover, in the case of an optical recording and reproducing apparatus which records and reproduces information on and from a recording medium with a plurality of recording layers as well as a recording medium with only a single recording layer, it become
Nakano Ikuo
Yamada Eiji
Conlin David G.
Edwards & Angell LLP
Psitos Aristotelis M
Sharp Kabushiki Kaisha
Tucker David A.
LandOfFree
Apparatus and method for optical recording/reproducing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for optical recording/reproducing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for optical recording/reproducing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3240212