Objective lens driving apparatus for optical disc player

Details Objective lens driving apparatus for optical disc player Objective lens driving apparatus for optical disc player

1998-07-23

2001-03-06

Ometz, David L. (Department: 2754)

Dynamic information storage or retrieval

Dynamic mechanism subsystem

Specified detail of transducer assembly support structure

C369S044150, C369S044220, C369S247100, C359S824000, C359S814000

Reissue Patent

active

RE037084

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an objective lens driving apparatus for use in an optical disc player which is adapted to optically read information from a disc-shaped recording medium by projecting a light spot onto the medium.
BACKGROUND ART
Known disc players of the kind described incorporate an optical pickup adapted to be moved linearly in the radial direction of a disc. A pickup is provided with an objective lens which is driven both in the focussing direction and tracking direction thus optically reading an information recorded in the disc. In order to attain a highly precise reading of the information in this type of optical disc player, therefore, it is necessary to conduct both focussing control for controlling the distance between the objective lens and the information track by moving the objective lens such as to eliminate any change in the distance attributable to distortion and oscillation of the disc, and tracking control for moving the objective lens in a manner to follow up the information track. These two types of control necessitate an objective lens driving apparatus capable of driving the objective lens both in the focussing direction and the tracking direction.
A known objective lens driving apparatus, which has been improved to some extent, will be explained hereinunder.
FIG. 1
is a perspective view of the known objective lens driving apparatus, while
FIG. 2
is an exploded perspective view of the same. An objective lens designated by reference numeral
1
is held by a holder
2
. The objective lens
1
is movably supported by web-like supporting members
4
which are made of a plastic material and fixed both to the holder
2
and a base
3
of the objective lens driving apparatus. U-shaped yokes
5
a,
5
b made of a magnetic material are fixed to the base by means of small screws
6
a to
6
d. Permanent magnets
7
a,
7
b are secured to respective yokes
5
a,
5
b in a manner to provide magnetic gaps between these permanent magnets and the associated yokes. Coils
8
a,
8
b are wound around the holder
2
.
This known objective lens driving apparatus operates in a manner which will be explained hereinunder.
The levels and polarities of electric currents supplied to the coils
8
a,
8
b are suitably controlled so that the holder
2
is electromagnetically driven by the electromagnetic forces exerted across the magnetic gaps formed between the permanent magnets
7
a,
7
b and the yokes
5
a,
5
b thereby moving the objective lens
1
two-dimensionally within a plane as indicated by arrows in FIG.
1
. Consequently, the objective lens
1
is moved in two directions, i.e., in the focussing direction and in the tracking direction, thus allowing a high accuracy in the reading of the information.
In this known objective lens driving apparatus, the objective lens is supported by the web-like supporting members
4
which are adapted to be flexed to permit the movement of the objective lens
1
both in the focussing direction and the tracking direction. This arrangement is complicated and raises the cost of production considerably and is liable to allow local partial resonance which impedes the operation of the apparatus tremendously. Namely, when the supporting members
4
are flexed in the focussing direction, stress is produced not only in the focussing direction but also in the tracking direction and an undesirable local resonance is caused by the stress acting in the tracking direction.
In this known objective lens driving apparatus, it is necessary that clearances between the holder
2
and the assemblies of the yokes
5
a,
5
b and permanent magnets
7
a,
7
b are controlled highly precisely. Furthermore, since the yokes
5
a,
5
b and the base
3
are formed as separate parts, there is a fear that the aforementioned gaps may be eliminated due to the sum of the dimensional errors of these parts. Therefore, it is required that these parts be finished within small tolerances, resulting in a raised cost of production of the parts.
The supporting members
4
in support of the objective lens are constructed such that the lens is held horizontally when no load is applied thereto. In the assembled state of the apparatus, therefore, the supporting members are deflected downwardly due to the weight of the lens and the holder, so that these supporting members tend to suffer from a torsional resonance. This problem can be solved by supplying the driving coils with biasing electric currents such as to raise the objective lens by the electromagnetic force produced by the biasing electric currents. This solution, however, causes other problems such as wasteful use of electric power and generation of heat.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the invention is to provide an objective lens driving device for optical disc players which is improved to reduce undesirable local resonance thereby obviating the above-described problems of the prior art.
To this end, the invention provides in its one aspect an objective lens driving device having a holder to which an objective lens is fixed, a base, and at least four linear members arranged in parallel and fixed at their both ends to said holder and said base, respectively, whereby said holder is resiliently supported on said base through said linear members both in the focussing direction and tracking direction.
The invention provides in another aspect an objective lens driving apparatus for an optical disc player comprising: an objective lens; a holder holding the objective lens; a tracking driving coil and a focussing driving coil fixed to the holder; a base; magnets fixed to the base and disposed in a manner to face the driving coils; and a supporting means having one end fixed to the holder and the other end fixed to the base and supporting the holder movably with respect to the base; wherein the improvement comprises that the supporting means exerting a biasing force of a level corresponding to the weights of the objective lens and the holder such that the centers of the driving coils correctly face the centers of the magnets when no electric current is supplied to the driving coils.
In still another aspect of the invention, two or more magnetic yokes are integrated into a single member so that the troublesome position control work is eliminated and the number of the parts is decreased so as to remarkably reduce the production cost of the apparatus.
In a further aspect of the invention, the yokes and the base of the objective lens driving apparatus is integrated into one body so as to reduce the overall height of the objective lens driving apparatus.


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