Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-08-08
2003-05-20
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044220
Reexamination Certificate
active
06567352
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an objective lens driving device and an optical disc apparatus using the objective lens driving device.
2. Description of Related Art
One type of objective lens driving device for use in an optical disc apparatus is disclosed in Japanese Laid-open Utility Model Application No. Hei-2-35330.
FIG. 9
shows the constitution of the objective lens driving device,
FIG. 10
is a cross-sectional view of the objective lens driving device which is taken along a line G—G of
FIG. 9
, and
FIG. 11
is a view of
FIG. 9
which is taken along the direction of an arrow H.
An objective lens
7
is provided in a lens holder
3
, which is supported and guided by a sliding shaft
6
which is slidably and rotatably disposed substantially in parallel to the optical axis direction of the objective lens
7
. A focusing coil
5
is wound around the outer peripheral surface of the lens holder
3
, and tracking coils
4
are provided at predetermined intervals in the peripheral direction on the outer peripheral portion of the lens holder
3
. A magnetic circuit comprising a magnet
2
, an outer yoke
1
and an inner yoke
9
is provided to generate magnetic flux so that the magnetic flux traverses the tracking coils
4
and the focusing coil
5
. The tracking coils
4
and the focusing coil
5
are supplied with current from current supply means such as a flexible printed circuit (hereinafter referred to as “FPC”).
During a focus control operation, the electromagnetic force acts in the direction of the sliding shaft
6
by causing the current to flow into the focusing coil
5
in the forward or reverse direction to move the objective lens
7
in the optical axis direction in accordance with the plane vibration of the recording surface of the optical disc, whereby the spot of the optical beam
8
can follow the recording surface of the optical disc. Further, during a tracking control operation, the electromagnetic force acts as a rotational couple of forces on the outer periphery of the sliding shaft
6
by causing the current to flow into each of the tracking coils
4
in the forward or reverse direction, whereby the spot of the optical beam
8
can follow the eccentricity of the track of the optical disc.
Next, the construction of a magnetic spring in a conventional objective driving device will be described by exemplifying an objective lens driving device disclosed in the official gazette for KOKOKU No. Hei-7-31814.
FIGS. 12 and 13
show an objective lens driving device having one objective lens which is used in a conventional CD apparatus or CD-ROM apparatus, wherein
FIG. 12
is a diagram showing the constitution of the objective lens driving device and
FIG. 13
is a cross-sectional view of the objective lens driving device which is taken along a line K—K of FIG.
12
.
In
FIGS. 12 and 13
, reference numeral
21
represents an objective lens for focusing an optical beam, reference numeral
22
represents a lens holder, reference numeral
28
-
1
,
28
-
2
represents a focusing coil, reference numeral
29
-
1
,
29
-
2
represents a tracking coil, reference numeral
25
represents a sliding shaft, reference numeral
23
represents an inner yoke, reference numeral
24
represents an outer yoke, reference numeral
26
-
1
,
26
-
2
represents a focusing magnet, reference numeral
27
-
1
,
27
-
2
represents a tracking magnet, and reference numeral
30
-
1
,
30
-
2
represents a magnetic substance for positioning the objective lens.
The focusing magnet
26
-
1
,
26
-
2
is magnetized to have bipolarity in the height direction, and the tracking magnet
27
-
1
,
27
-
2
is magnetized to have bipolarity in the peripheral direction. The magnetic density distribution in the peripheral direction in the neighborhood of the magnetic substance
30
-
1
,
30
-
2
which confronts the focusing magnet
26
-
1
,
26
-
2
is maximized at the center of the magnet, and thus the magnetic substance
30
-
1
,
30
-
2
is magnetically balanced and stable at the position confronting to the center of the focusing magnet. Paying attention to the flow of the magnetic flux in the height direction, the magnet substance
30
-
1
,
30
-
2
is magnetically balanced and stable in the neighborhood of the boundary of the N and S poles of the focusing magnet
26
-
1
,
26
-
2
so as to form a magnetic loop of the N pole of the focusing magnet
26
-
1
,
26
-
2
→the magnetic substance
30
-
1
,
30
-
2
→S pole→N pole. Accordingly, the objective lens
21
can be stably positioned by the magnetic balance in the rotational direction (tracking direction) and the height direction (focusing direction) with respect to the sliding shaft
25
.
SUMMARY OF THE INVENTION
Recently, there has been adopted a method of increasing the number of rotation of an optical disc so as to increase the data transfer rate from an optical disc apparatus, and it has become more and more necessary to enhance the follow-up property (responsibility) of the objective lens of the objective lens driving device to the plane vibration and the track eccentricity of the recording surface of the optical disc. Particularly, the acceleration of distortion due to the eccentricity of the track is rapidly increased because it is proportional to the square of the number of rotation, and thus the follow-up performance of the objective lens in the tracking direction is required to be enhanced. A method for intensifying the electromagnetic force of the coil in a gap of a magnetic circuit may be considered to enhance the follow-up performance of the objective lens. In order to intensify the electromagnetic force of the coil, the effective portion of the coil in the gap of the magnetic circuit may be lengthened. However, in the objective lens driving device shown in
FIGS. 9
to
11
, the lowermost portion of the tracking coil
4
in the sliding axis direction is set to be equal to the lowermost portion of the focusing coil
5
in height. Therefore, in order to prevent the optical beam
8
from being intercepted by the coil when the effective portion of the coil is lengthened, it is necessary that the optical beam
8
is disposed so as to pass over the lower side of the focusing coil
5
and the tracking coil
4
in the sliding shaft direction, or incident from the optical axis direction of the objective lens
7
. Consequently, the objective lens driving device is bulky, and thus the optical disc apparatus must be designed in a large size. Further, the optical disc apparatus is also required to be compact in addition to the requirement of the enhancement of the follow-up performance of the objective lens of the objective lens driving device to the plane vibration and the track eccentricity of the recording surface of the optical disc. Therefore, the objective lens driving device is required to be thin and compact. According to the first objective lens shown in
FIGS. 9
to
11
, if the follow-up performance of the objective lens is enhanced, the objective lens driving apparatus would be bulky (thick). That is, it is impossible to satisfy both the requirement for the enhancement of the follow-up performance of the objective lens and the requirement for the thin (low-profile) and compact design of the objective lens driving device.
According to the present invention, an objective lens driving device comprises a movable unit having an objective lens for focusing an optical beam onto an optical disc, a focusing coil for driving the objective lens in an optical axis direction thereof, a tracking coil for driving the objective lens in a radial direction of the optical disc and a lens holder for holding the objective lens, the focusing coil and the tracking coil, a sliding shaft which is provided substantially in parallel to the optical axis direction of the objective lens and adapted to guide the movable unit, a magnetic circuit for generating magnetic flux which is applied to the focusing coil and the tracking coil, and a mirror for converting the optical beam in the optical axis direct
Inui Shinro
Izumi Katsuhiko
Kuroda Naomitsu
Miura Michio
Mizuno Ryuichiro
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