Optical: systems and elements – Lens – With support
Reexamination Certificate
2000-11-01
2001-09-04
Ben, Loha (Department: 2873)
Optical: systems and elements
Lens
With support
C359S814000, C359S824000, C369S044140, C369S044150, C369S247100
Reexamination Certificate
active
06285517
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pick-up device for optically writing information into and reading out the same from a recording medium layered on an optical disc by projecting a light beam onto the recording medium. More particularly, the invention relates to an objective lens driver, used for an optical pick-up device, in which a movable portion having an objective lens is supported by means of suspension wires.
2. Discussion of Background Art
Generally, an optical pick-up device is composed of an objective lens driver having an objective lens and an optical system for transmitting light to and receiving the same from the objective lens. The optical pick-up device is mounted on a mounting table of an optical system block.
A general objective lens driver, as shown in
FIG. 15
, includes a movable portion
1
, a fixed portion
2
, and four elastic supporting members
3
. The movable portion
1
includes an objective lens
11
, a focus coil
12
and a tracking coil
13
. The fixed portion
2
includes a magnetic circuit (magnet and others)
21
. The elastic supporting members
3
are fastened at both ends thereof to the movable portion
1
and the fixed portion
2
, and support the movable portion
1
in a cantilever fashion. The elastic supporting members
3
being metal suspension wires are disposed such that pairs of elastic supporting members are respectively provided on both sides of the movable portion
1
with respect to the objective lens
11
. One ends of the pairs of the elastic supporting members
3
are soldered to holder plates
15
, while the other ends of them are soldered to a base plate
23
. The holder plates
15
are provided on the right and left sides of a lens holder
14
holding the objective lens
11
. The fixed portion
2
is disposed so that the elastic supporting members
3
are parallel to a tangential direction of the disc.
The movable portion
1
may be shifted in a focus direction (perpendicular to the disc surface) when current is fed to the focus coil
12
, and in a tracking direction (radial direction of the disc) when current is fed to the tracking coil
13
. A measure to damp vibrations of the movable portion
1
is taken. As well illustrated in
FIG. 16
, damper cases
24
are provided on the front side of the base plate
23
to which the other ends of the elastic supporting members
3
are fastened. The other ends of the elastic supporting members
3
, as shown, are passed through the damper cases
24
and the base plate
23
, and soldered to the outer side of the base plate
23
. The damper cases
24
are filled with gel-like damping material
25
. In this case, the elastic supporting members
3
placed in part are stuck with the damping material
25
. When the movable portion vibrates, the elastic supporting members
3
move through the damping material within the damper cases. At this time, viscous flow of the damping material acts on the moving elastic supporting members, and the supporting members are deformed. The deformation of the supporting members and the viscous flow of the damping material are utilized for the damping of the vibrations of the movable portion. (This damping technique is disclosed in JP-A-2-232824.)
To secure an exact information writing/reading to and from the optical disc, it is required that the optical axis of the objective lens is perpendicular to the surface of the disc. If the optical axis of the objective lens is tilted with respect to the disc surface during a movement of the movable portion (including the objective lens) of the objective lens driver in the focus direction, coma occurs in the optical system and consequently a signal jitter increases. A tangential directional component and a radial directional component make up the tilt of the objective lens. To secure an exactness of the information writing/reading, tilts of those directional components need to be eliminated.
For this reason, in the objective lens driver, the objective lens is mounted on the mounting table such that the optical axis of the objective lens is perpendicular to the disc surface. To this end, the supporting mechanism of the movable portion is designed such that the angular relation of the objective lens of the disc surface is maintained irrespective of the moving directions of the movable portion, the focus direction and the tracking direction.
In the objective lens driver, referred to above, in which the movable portion is supported by the elastic supporting members, the perpendicularity of the optical axis of the objective lens to the disc surface is maintained irrespective of the moving direction of the movable portion if the elastic supporting members have equal lengths and the spatial intervals between both ends of the elastic supporting members are equal.
To prevent the movable portion
1
, or the objective lens
11
, from being tilted when the movable portion is moved in the focus direction or the radial direction, the background art mentioned above has the following construction: the distances between the fixing ends of the elastic supporting members
3
in the movable portion
1
and the fixing ends thereof in the fixed portion
2
are selected to be equal and those elastic supporting members
3
are disposed to be parallel to one another in the vertical and horizontal directions. Further, the amounts of the damping material
25
contained in the damper cases
24
are selected to be equal to each other on the assumption that the elastic supporting members
3
are fixed at predetermined positions. Spring constants of the elastic supporting members
3
are selected to be equal to one another. When the movable portion
1
is moved in the focus direction, it can be considered that a focus-directional drive force acts on the center of gravity of the movable portion
1
. Hence, the gravity center position is coincident with the focus directional drive center position.
To suppress the resonance in a low frequency region, damping material is put around each wires in the objective lens driver. Use of only the damping material fails to satisfactorily suppress the resonance in a high frequency region by pitching or yawing, however. To cope with this, JP-A-7-105551 and JP-A-9-190636 disclose objective lens drivers in that with the intention of improvement of the high-frequency resonance suppression, the movable portion
1
is supported with the fixed portion
2
in a state that the elastic supporting members
3
are bent in advance in radial direction, as shown in FIG.
17
.
In the structure where the elastic supporting members
3
are arcuately bent in advance, the movable portion
1
unavoidably tilts when the movable portion
1
is shifted in the focus direction, even if the spatial intervals between the fixing points of the four elastic supporting members
3
are set to be equal to one another, and those members are disposed strictly parallel to each other. In case where the elastic supporting members
3
are bent in the radial direction, for example, when the movable portion
1
is shifted in the focus direction, its tilting in the tangential direction increases. Particularly when the damping resonating with high frequencies is increased by increasing a quantity of the bending of the elastic supporting members, a tilt of the movable portion
1
in the tangential direction increases. When the tilt of the movable portion
1
, i.e., the tilt of the objective lens
11
, increases, coma is produced and readout signal jitter increases.
Where the quantity of the bending of the elastic supporting members
3
is reduced with the intention of reducing the tilt of the movable portion
1
in the tangential direction when the movable portion
1
is shifted in the focus direction, the damping effect for the high frequency resonance is lowered. This is problematic when it is assembled into a system.
Thus, the decrease of the tilt of the movable portion
1
in the tangential direction contradicts the increase of the damping for the high frequency resonance suppression.
In the
Kawano Noriyuki
Terasaki Yasuhiro
Uekusa Nobuo
Ben Loha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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