Optical: systems and elements – Lens – With support
Reexamination Certificate
2003-03-25
2004-09-14
Ben, Loha (Department: 2873)
Optical: systems and elements
Lens
With support
C359S813000, C359S814000, C369S044150, C369S215100, C369S221000, C369S244100
Reexamination Certificate
active
06791772
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an objective lens driver for use in an optical disc drive for reading and/or writing information optically from/onto a disk storage medium by focusing a light beam thereon.
2. Description of the Related Art
An optical disc drive for reading and/or writing information optically from/onto a disk storage medium such as a compact disc (which will be simply referred to herein as an “optical disc”) includes an optical head. The optical head moves in the radial direction of the disc, thereby focusing a light beam onto a predetermined track to read or write information therefrom/thereon. Also, the optical head detects the light beam that has been reflected from the disc and converts the light detected into an electric signal.
The optical head includes a light source and an objective lens for use to focus the light beam that has been emitted from the light source. The optical head drives the objective lens such that a beam spot, formed on the disc by the light beam focused thereon, follows predetermined tracks on the disc while maintaining a constant focusing state. More specifically, the objective lens is driven both perpendicularly and parallelly to the information recording side of the disc in such a manner as to correct a focus error and a tracking error, which may be caused by the flutter and eccentricity of the disc, respectively. The former direction that is perpendicular to the information recording side of the disc is parallel to the optical axis of the objective lens, and will be referred to herein as a “focusing direction”. On the other hand, the latter direction that is parallel to the information recording side of the disc is the disc radial direction, and will be referred to herein as a “tracking direction”. Such a mechanism which is specially designed to drive the objective lens will be referred to herein as an “objective lens driver”. It should be noted that the objective lens herein forms an integral part of the objective lens driver.
Recently, the optical discs should have even higher storage capacities and the optical disc drives should achieve even higher transfer rates year after year. To meet these demands, it has become increasingly necessary to perform even more precise positioning control on the objective lens and transfer information, which has been read out from, or is going to be written on, an optical disc rotating at a high speed, from/to the optical disc at an even higher rate.
When the optical disc is rotated at a high speed, the acceleration of the flutter and the acceleration of the eccentricity both increase in proportion to the square of the rotational speed of the disc. Accordingly, if the acceleration at which the objective lens of the objective lens driver is moving is not sufficiently sensitive to these accelerations, then the objective lens cannot follow any variation in flutter or eccentricity closely, thus causing control errors. In that case, the light beam will be out of focus with the disc surface or go off the predetermined tracks on the disc to possibly deteriorate the quality of a read or write signal.
On the other hand, the optical disc drives are recently required to further reduce their sizes. To meet those demands, the objective lens drivers also need to reduce their sizes (e.g., their thicknesses, in particular). Thus, it has become more and more difficult to obtain an objective lens driver that can exhibit sufficient acceleration sensitivity within a limited space.
Hereinafter, a conventional objective lens driver with a reduced thickness will be described with reference to
FIGS. 15
,
16
,
17
A,
17
B and
17
C.
FIG. 15
is an exploded perspective view illustrating the structure of a conventional objective lens driver.
FIG. 16
is a plan view of the objective lens driver shown in FIG.
15
.
FIG. 17B
is a schematic plan view showing the positional relationship among magnets, a focusing coil and a tracking coil in the conventional objective lens driver.
FIGS. 17A and 17C
are transparent plan views of the objective lens driver as respectively viewed in the directions U and V shown in FIG.
17
B.
In the conventional objective lens driver, an objective lens
1
is fitted into a lens holder
301
as shown in
FIGS. 15 and 16
. The lens holder
301
has a central through hole to receive a substantially pentagonal prism focusing coil
302
with a pair of flat and substantially quadrangular prism tracking coils
303
. The two tracking coils
303
are connected in series together.
Two magnets
304
and
305
are secured to a base
306
so as to sandwich the focusing coil
302
and the tracking coils
303
with a gap provided between them. A holder
308
is secured to the base
306
. A fixing substrate
310
is attached to the back of the holder
308
.
A pair of junction terminal plates
309
is secured onto the two side surfaces of the lens holder
301
. Four wires
307
a
,
307
b
,
307
c
and
307
d
are connected to the junction terminal plates
309
such that one end of each of the wires
307
a
through
307
d
is soldered up with associated one of the junction terminal plates
309
. The other end of the wires
307
a
through
307
d
is soldered up with the fixing substrate
310
.
Thus, a movable body is made up of the objective lens
1
, lens holder
301
, focusing coil
302
, tracking coils
303
and junction terminal plates
309
. That is to say, this movable body is supported by the four wires
307
a
through
307
d
so as to be movable both in a focusing direction F and in a tracking direction T with respect to the base
306
.
The wires
307
a
through
307
d
may be made of an elastic metal material such as beryllium copper or phosphorus bronze, for example. The two terminals of the focusing coil
302
and the four terminals of the pair of serially connected tracking coils
303
are electrically connected to the fixing substrate
310
by way of the junction terminal plates
309
and the wires
307
a
through
307
d.
Also, as shown in
FIG. 16
, the magnets
304
and
305
are arranged such that different poles of the magnets
304
and
305
face with other and have substantially the same size J in the tracking direction T.
In the conventional objective lens driver having such a structure, a driving force is generated from portions of the focusing coil
302
and tracking coils
303
, which are sandwiched between the magnets
304
and
305
. The driving force generating point is located substantially at the center of the movable body. By shifting the location of the objective lens
1
from that driving force generating point, no mechanical interference will occur between a reflective mirror (not shown) for reflecting the light beam in the focusing direction F and the driving means consisting of the magnets
304
and
305
, focusing coil
302
and tracking coils
303
. In this manner, an objective lens driver with a reduced thickness, which can be used effectively in an optical head with a reduced thickness, is obtained.
Hereinafter, it will be described with reference to
FIGS. 17A through 17C
how the conventional objective lens driver having such a configuration operates.
First, a focusing drive operation thereof will be described. As shown in
FIG. 17A
, when a current is supplied to the focusing coil
302
so as to flow in the direction pointed by the arrow If, a driving force is generated in the direction pointed by the arrow Pf along one side of the focusing coil
302
because the opposed magnetic pole is the N pole. As a result, the lens holder
301
is driven in the focusing direction F by the driving force Pf that has been generated in the focusing coil
302
.
Next, a tracking drive operation thereof will be described. As shown in
FIG. 17C
, when a current is supplied to the tracking coils
303
so as to flow in the direction pointed by the arrow It, a driving force is generated in the direction pointed by the arrow Pt along one side of the tracking coils
303
because the opposed magnetic pole is the S pole. As a result, the l
Ikawa Yoshihiro
Wakabayashi Kanji
Yamamoto Hiroshi
Akin Gump Strauss Hauer & Feld & LLP
Ben Loha
Matsushita Electric - Industrial Co., Ltd.
LandOfFree
Objective lens driver does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Objective lens driver, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Objective lens driver will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3206763