Optical: systems and elements – Lens – With support
Reexamination Certificate
2000-05-11
2001-10-23
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With support
C359S813000, C359S824000, C369S044140, C369S112240
Reexamination Certificate
active
06307687
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup device using an objective lens which is a two-group lens comprised of a first lens and a second lens. More particularly, the invention relates to an optical pickup device in which the distance between the first lens and the second lens is variable and in which the objective lens is driven in focusing and tracking directions.
Conventionally, as a recording medium for information signals, there have been proposed various optical recording media such as so-called optical disks, magneto-optical disks or optical cards. Further, there has been proposed an optical pickup in which light from a light source is beamed onto such an optical recording medium as described above to implement write and read of information signals on a signal recording surface of the optical recording medium. This optical pickup is capable of converging light onto the signal recording surface of the optical recording medium with a reduced beam diameter of the light by enlarging the numerical aperture (NA) of the objective lens, and thus capable of improving the information recording density of the optical recording medium.
In the case of a single lens used as this objective lens, refractive power would be required in an attempt to obtain a high numerical aperture. However, enlarging the refractive power would cause the curvature of the lens surface to decrease, making positioning accuracy between refraction planes stricter. From these and other reasons, the numerical aperture of the single lens has hitherto been limited to about 0.6.
In an optical disk, which is an optical recording medium, if the thickness of a protective layer that protects the signal recording surface deviates from a specified value, spherical aberration largely changes. At the same time, the spherical aberration is proportional to the fourth power of the numerical aperture, neglecting the terms of higher orders. Therefore, with the numerical aperture of the objective lens increased, manufacturing tolerance for the protective layer thickness of the disk would be narrower.
In contrast to this, with the use of a two-group lens, the tolerance for design of the protective layer thickness of the disk can be a wide one while a high numerical aperture is enabled. For this reason, attention has been paid to use of a two-group lens as a high numerical aperture objective lens.
Among pickup devices using a two-group lens as shown above, one described in Japanese Patent Laid-Open Publication HEI 10-255290 is shown in
FIG. 6
in its structure.
The two-group lens is comprised of a first lens
102
, and a second lens
103
opposed to the first lens
102
with a gap
119
provided therebetween. Further, the two-group lens
120
is equipped with a variable-distance driver
116
for making the distance between the first lens
102
and the second lens
103
variable.
Also, the two-group lens
120
includes, in addition to the first lens
102
and the second lens
103
, a generally cylindrical bobbin
118
for holding the first lens
102
with an outer peripheral portion of the first lens
102
fitted thereto, a yoke
110
disposed at a disk-side outer peripheral portion of the second lens
103
with the gap
119
formed against the bobbin
118
, a coil
111
wound around an outer peripheral portion of the bobbin
118
, a magnet
112
mounted on the yoke
110
and spaced from the coil
111
, a spring
113
for mechanically coupling the bobbin
118
and the yoke
110
to each other, and a protective material
115
disposed at an outer peripheral portion of a disk-side surface of the first lens
102
.
An electric current, when applied to this coil
111
, causes a Lorentz force to be generated in combination with magnetic fields generated by the magnet
112
facing the coil
111
. The spring
113
mechanically couples the bobbin
118
and the yoke
110
together, thereby elastically supporting the bobbin
118
against the yoke
110
. Also, the spring
113
supports the bobbin
118
so that the bobbin
118
is movable only in the optical-axis direction. Then, in the two-group lens
120
, the bobbin
118
, the yoke
110
, the coil
111
, the magnet
112
and the spring
113
constitute a so-called voice coil motor, thereby forming part of the variable-distance driver
116
. That is, in the two-group lens
120
, the distance between the second lens
103
and the first lens
102
that is elastically supported against this second lens
103
via the yoke
110
, the spring
113
and the bobbin
118
with a degree of freedom in the optical-axis direction is made variable by the variable-distance driver
116
driven by the Lorentz force generated between the coil
111
and the magnet
112
. In addition, in the optical pickup, the two-group lens
120
equipped with the variable-distance driver
116
is supported by an objective-lens driving actuator so as to be movable in a direction along the optical axis of a laser beam emitted by a semiconductor laser as well as in a direction vertical to the optical axis.
When the lens-to-lens distance of the two-group lens is made variable depending on the protective layer thickness and refractive index as in the above-shown prior art, the center-of-gravity position of the movable part in the objective-lens driver varies in the optical-axis direction.
In this case, when an external force in the tracking direction is applied by the objective-lens driver, there occurs a rolling about an axis vertical to the optical-axis direction and to the tracking direction. Further, whereas a relatively small amount of rolling results for a small moving velocity in the tracking direction, increasing the moving velocity higher causes the rolling amount to increase and moreover resonance of the rolling mode to occur, thus making correct tracking no longer implementable.
Also, since the current to be applied to the variable-distance driver depending on differences in protective layer thickness and refractive index is passed generally in DC manner, there is a further problem of increased electric power consumption.
The present invention having been achieved in view of the above circumstances, an object of the invention is to provide an objective lens for use in an optical pickup, the objective lens being a two-group lens comprised of a first lens and a second lens, in which objective lens the resonance of a rolling mode due to a shift between a point of action in the tracking direction and the center of gravity resulting from driving operation by the variable-distance driver is suppressed within a controllable range so that an accurate tracking can be achieved, and further in which objective lens the value of electric current applied to the variable-distance driver is reduced so that the distance between the first lens and the second lens can be ensured with a simple structure, thus the objective lens having a compact constitution.
SUMMARY OF THE INVENTION
In order to achieve the object, there is provided an optical pickup device having: an objective lens comprised of a first lens having a surface facing an information recording medium and a second lens on which a beam derived from a light source becomes incident; an objective lens driver for driving the objective lens in an optical-axis direction and in a direction vertical to the optical axis; and a variable-distance driver for changing a distance between the first lens and the second lens, the optical pickup device further comprising:
a mass body driver for driving a portion of movable part of the objective lens driver in such a way that when the distance between the first lens and the second lens is changed by the variable-distance driver, a center-of-gravity position of the movable part of the objective lens driver is located generally coincident with a point of action of driving forces in the optical-axis direction and in the direction vertical to the optical axis generated by the objective lens driver, or closer to the light source than the point of action.
According to the above construction, when the distance betwee
Conlin David G.
Dike, Bronstein, et al. of Edwards & Angell
Epps Georgia
Seyrafi Saeed
Sharp Kabushiki Kaisha
LandOfFree
Optical pickup device capable of accurate tracking with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical pickup device capable of accurate tracking with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical pickup device capable of accurate tracking with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2573333