Optical: systems and elements – Lens – With support
Reexamination Certificate
2000-09-28
2002-02-05
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With support
C359S814000, C369S044150
Reexamination Certificate
active
06344936
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an objective lens driving apparatus, and more particularly to an objective lens driving apparatus provided in an apparatus for optically recording and reproducing information by a light spot irradiated on a disc-shaped recording medium.
An objective lens driving apparatus is used in an optical disc drive which records and reproduces information represented by sequence of pits by irradiating a light beam spot on a disc-shaped information recording medium (hereinafter is referred to as disc) such as a compact disc. The objective lens driving apparatus drives an objective lens so that the light beam spot is accurately applied to a predetermined position on the disc. A focusing error and a tracking error ordinarily arise between the pit sequence on the rotating disc and the light beam spot. The focusing error is caused by vibration of a disc face in the axial direction (hereinafter is referred to as face vibration) and the tracking error is caused by eccentricity of the disc. To correct these errors, the objective lens driving apparatus controls the objective lens in a direction perpendicular to the disc face (hereinafter is referred to as focusing direction) as well as in the radial direction of the disc (hereinafter is referred to as tracking direction) so that an adequately focused light beam spot continues to trace accurately the pit sequence.
In CD-ROM drives, DVD-ROM drives, etc. usedwith personal computers, the increase of a data transfer speed is required with the improvement of processing performance of the computer. To increase the data transfer speed, it has been practiced to increase the disc rotational speed, thereby realizing a high speed recording and reproducing operation. However, with the increase of the disc rotational speed, the objective lens is required to be controlled at higher speeds to follow with vibrations caused by the face vibration varying at a high speed and disc eccentricity. In order to reply to the above-mentioned demand, a high acceleration sensitivity is required in the objective lens driving apparatus. The acceleration sensitivity is defined as the ratio of a current supplied to the objective lens driving apparatus to an acceleration when the objective lens moves. It is known that the acceleration sensitivity required to the objective lens driving apparatus increases with the square of the revolution speed of the disc.
In order to increase the acceleration sensitivity in the objective lens driving apparatus, the moving member on which the objective lens is mounted has been reduced in weight, and improvements are made in the magnetic circuit used to generate the driving force. A prior art objective lens driving apparatus will be described below with reference to drawings.
FIG. 12
is a perspective view of relevant parts of the prior art objective lens driving apparatus.
In
FIG. 12
, an objective lens
101
and a printed coil board
104
are rigidly fixed to a lens holder
102
to construct a moving member
100
. Suspension wires
103
a
,
103
b
, and
103
c
, and a suspension wire
103
d
located below the suspension wire
103
c
and hidden from view in the drawing, are each fastened at one end to the lens holder
102
and at the other end to a wire holder
111
. The wire holder
111
is fixed to a base
110
. Two yoke bases
107
a
and
107
b
are mounted on the base
110
in opposed relationship. Magnets
108
a
and
108
b
are mounted on the opposing surfaces of the yoke bases
107
a
and
107
b
, respectively, thereby forming a magnetic circuit. The printed coil board
104
is located between the magnets
108
a
and
108
b.
FIG. 13
is a plan view of the printed coil board
104
and the magnets
108
a
and
108
b
, as seen in the direction of arrow V in FIG.
12
. In
FIG. 13
, one focusing coil
105
and four tracking coils
116
to
119
are mounted on the printed coil board
104
. Arrow Fo in the figures indicates the moving direction of the printed coil board
104
for focusing action (hereinafter is referred to as the focusing direction), and arrow Tk indicates the moving direction of the same for tracking action (hereinafter is referred to as tracking direction).
In
FIG. 13
, the focusing coil
105
substantially rectangular in shape is located in the central portion of the printed coil board
104
. A current flows through the focusing coil
105
in the direction shown by arrow If (hereinafter is referred to as current If). Two tracking coils
116
and
117
substantially rectangular in shape are located at the left side of the focusing coil
105
, and two tracking coils
118
and
119
substantially rectangular in shape are located at the right side thereof. The four tracking coils
116
to
119
are wired so that a current flows in the direction indicated by arrow It (hereinafter is referred to as current It). The printed coil board
104
includes one layer or a plurality of layers. When the printed coil board
104
includes a plurality of layers, the focusing coil
105
and the tracking coils
116
to
119
are respectively wired so that the current flows in the same direction in any of the coils on the respective layers.
In FIG.
12
and
FIG. 13
, the dimensions of the magnets
108
a
and
108
b
are determined so that their left and right sides align with the centers of the left-side tracking coils
116
,
117
and the right-side tracking coils
118
,
119
, respectively. The vertical dimension of each of the magnets
108
a
and
108
b
is made larger than the vertical dimension of any of the focusing coil
105
and the tracking coils
116
to
119
. The magnets
108
a
and
108
b
are magnetized so that each magnet has one magnetic pole (for example, N pole) on the surface thereof facing to the printed coil board
104
and the opposite magnetic pole (for example, S pole) on the opposite surface thereof. In
FIG. 13
, on the upper half sections of the magnets
108
a
and
108
b
sectioned by a magnetization boundary line MB of a horizontal dashed line; the magnetic lines of forces are directed from a viewer of the figure into behind the paper face of the figure, and in the lower half section, the magnetic lines of forces are directed from behind the paper face of the figure toward the viewer. The magnetization boundary line MB indicates that the magnetization state is reversed across the boundary line. The magnets
108
a
and
108
b
are magnetized so that the opposite magnetic poles face each other with the printed coil board
104
interposed therebetween.
When the current If flows through the focusing coil
105
, winding portions
105
a
of the focusing coil
105
on two sides perpendicular to the focusing direction Fo receive an electromagnetic force in the focusing direction Fo in accordance with Fleming's rules. As a result, the moving member
100
is driven in the focusing direction Fo. In winding portions
116
a
to
119
a
and
116
b
to
119
b
of the tracking coils
116
to
119
on respective two sides perpendicular to the tracking direction Tk, the winding portions
116
b
to
119
b
on the sides nearer to the focusing coil
105
are located within the magnetic field of the magnets
108
a
and
108
b
. When the current It flows through the tracking coils
116
to
119
, the winding portions
116
b
to
119
b
receive the electromagnetic force in the tracking direction Tk in accordance with Fleming's rules, and the moving member
100
is driven in the tracking direction. Improvements are intended for focusing drive sensitivity and tracking drive sensitivity by placing the printed coil board
104
within the magnetic field of high magnetic flux density formed by the two opposing magnets
108
a
and
108
b
. Where, the focusing drive sensitivity is defined as the ratio (LF/If) of a moving distance LF of the moving member
100
in the focusing direction Fo to the current If flowing through the focusing coil
105
, and the tracking drive sensitivity is defined as the ratio (LT/It) of a moving distance LT of the moving member
100
in the tracking d
Mohri Masanari
Santo Takeo
Wakabayashi Kanji
Yamamoto Hiroshi
Mack Ricky
Pearne & Gordon LLP
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