Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-09-27
2002-07-09
Edun, Muhammad (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044170, C359S814000
Reexamination Certificate
active
06418094
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to an optical pick-up device for reading and writing information from and to an optical disc such as a CD. More particularly, the invention relates to an improvement in arrangement of a tracking coil and a magnet in the optical pick-up device. Furthermore, the invention relates to an improvement in a magnetic spring for holding a lens holder having an objective lens in a magnetic neutral position.
2. Related Art
As shown in
FIGS. 10 and 11
, an optical pick-up device
900
comprises a driven portion
904
rotatably supported on a casing
901
around a central shaft
902
and including an optical system having an objective lens
903
, a focus coil
905
and a tracking coil
906
which are attached to the driven portion
904
, and a magnet
907
fixed to the casing
901
opposite to each tracking coil
906
. A part of the casing
901
is provided as a yoke on the inside of the driven portion
904
and forms a parallel magnetic flux together with the magnet
907
.
Furthermore, the tracking coil
906
is wound like a rectangle on the side surface of the driven portion
904
and is provided such that one side (hereinafter referred to as a driving side)
908
along the center
902
is positioned in the parallel magnetic flux. In consideration of a reduction in the size of the optical pick-up device
900
, the tracking coils
906
are provided on the opposite side of the objective lens
903
with the central shaft
902
interposed therebetween.
In the optical pick-up device
900
, the tracking coil
906
is conducted so that force for rotating the driven portion
904
is generated. Thus, a tracking operation can be carried out.
In the optical pick-up device, however, each tracking coil
906
is provided asymmetrically with respect to the central shaft
902
. Therefore, when one of the tracking coils
906
approaches the magnet
907
during a tracking operation, the other tracking coil
906
goes away from the magnet
907
. In other words, the tracking coils
906
have different positional relationships with the magnet
907
during the tracking operation, respectively. Consequently, the tracking coil
906
is varied on a magnetic circuit basis.
In addition, an opposite side
909
to be conducted in a reverse direction to the driving side
908
is sometimes affected by a magnetic field leakage from the magnet
907
. For this reason, a phase disturbance is apt to be caused in a high-frequency region as shown in FIG.
12
.
In the optical pick-up device
900
, moreover, a magnetic spring for holding the driven portion
904
in the magnetic neutral position can be constituted by the magnet
907
and a magnetic piece
910
opposed to a region in which the magnetic field strength of the magnet
907
is changed.
The magnet
907
is magnetized uniformly. In general, therefore, it is necessary to provide the magnetic piece
910
in a position opposed to the outer peripheral edge of the magnet
907
.
In many cases, however, the magnet has a large dimension and a space for attaching the magnetic piece cannot be kept in a position opposed to the outer peripheral edge. In particular, in the case in which the magnetic piece is to be provided on the outer peripheral edge of the magnet in a focusing direction, the magnetic piece should be provided in the position opposed to the outer peripheral edge of the magnet on the opposite side of an optical recording medium because there is no space on the optical recording medium side. As a result, the thickness of the optical pick-up device is determined depending on a dimension in the focusing direction occupied by the magnet and the magnetic piece opposed to the outer peripheral edge, which is not preferable for a reduction in the thickness of the device.
SUMMARY OF INVENTION
It is an object of the invention to provide an optical pick-up device which prevents a positional relationship with a magnet from being varied for each tracking coil during a tracking operation and prevents a side opposed to a driving side of the tracking coil from being affected by a magnetic field leakage.
It is another object of the invention to provide a magnetic spring for holding a lens holder in a magnetic neutral position without preventing a reduction in a thickness.
REFERENCES:
patent: 5513047 (1996-04-01), Matsui
Ishikawa Masayuki
Kamada Toru
Ozawa Takeshi
Edun Muhammad
Kabushiki Kaisha Sankyo Seiki Seisakusho
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