JP2554001Y2 - Lens drive - Google Patents

Description

TECHNICAL FIELD The present invention relates to a lens driving device for a pickup unit in an optical information reading device. BACKGROUND ART An optical information reading apparatus focuses and irradiates a recording track formed on an information recording surface of a recording medium with a laser beam for information reading as spot light, and detects a change in reflected light from the information recording surface to obtain information. Is to read. For this purpose, it is necessary to always focus the laser beam for reading information on the recording track despite the surface contact caused by the warpage of the recording medium. It is configured so that focus adjustment (focus servo) can be performed by slightly moving in a direction perpendicular to the direction.
In addition, since the laser beam must always accurately track the recording track regardless of the eccentricity of the recording track, the objective lens is minutely moved in a direction perpendicular to the recording track (tracking servo). Have been. A lens driving device shown in FIG. 4 (a) has already been developed for moving the objective lens. In an already developed lens driving device, as shown in FIG. 4 (a), an objective lens 1 is attached to a lens holder 2 to irradiate a spot light on a recording surface of a recording medium (not shown). I have. The lens holder 2 has a hollow portion 3 penetrating therethrough. One focusing coil 4 and two tracking coils 5 are fixed in the hollow portion 3. The focusing coil 4 is fixed so that the center axis of the coil is parallel to the optical axis of the objective lens 1.
The tracking coil 5 is arranged so that the center axis of the coil is perpendicular to the optical axis of the objective lens 1.
Is attached to the outer peripheral surface. Focusing coil 4,
The lens holder 2 to which the tracking coil 5 and the objective lens 1 are fixed is attached to the free ends of four cantilever-shaped support members 6 extending in a direction perpendicular to the optical axis direction of the objective lens 1. ing. On the other hand, the fixed end of the support member 6 is fixed to the base 7. Since the four support members 6 are flexible, the lens holder 2 is movable in the optical axis direction of the objective lens 1 (arrow F direction) and in a direction perpendicular to the optical axis direction (arrow T direction). It has become. However, this movement is with respect to the base 7. In the hollow part 3 of the lens holder 2 supported movably in two directions with respect to the base 7, the focusing coil 4 and the tracking coil 5 fixed there are fixed.
The magnet 8 and the yoke 9 which generate a magnetic flux interlinking with the yoke 9 are inserted. A magnet 8 and a yoke 9 preferably made of a ferromagnetic material constitute a magnetic circuit, which is provided with a single magnetic gap 10 for producing a parallel magnetic flux. The magnet 8 and the yoke 9 are inserted into the hollow part 3 of the lens holder 2 so that a part of the focusing coil 4 and a part of the tracking coil 5 are located as the working sides 4a and 5a in the magnetic gap 10. The working sides 4a and 5a referred to here are, when current is supplied to the focusing coil 4 and the tracking coil 5, the coils 4 to which the electromagnetic force acts in the directions of arrows F and T in the magnetic gap 10 where the parallel magnetic flux exists. , Means part of 5. As described above, the magnet 8 and the yoke 9 inserted into the hollow portion 3 are attached to a fixing member (not shown) fixed to the base 7. In the lens driving device configured as described above, the objective lens 1 can be driven in the direction of arrow F together with the lens holder 2 by supplying a current to the focusing il 4, and the objective lens is supplied by supplying a current to the tracking coil 5. Can be driven together with the lens holder 2 in the direction of arrow T. However, in the above-described lens driving device, the working side 4a of the focusing coil 4 is located at the center of gravity of the movable portion including the objective lens 1, the focusing coil 4, the tracking coil 5, and the lens holder 2.
Deviation occurs between the the central point of application of the electromagnetic force C ₅ and centroid acting By matching action center point C ₄ of the electromagnetic force to act sides 5a of the tracking coil 5 acting. This can be easily understood from the cross sections of the focusing coil 4 and the tracking coil 15 shown in FIG. When the action center point C ₅ of the electromagnetic force acting on the working side 5a of the tracking coil 5 in the reverse match the centroid, the action center point C ₄ of the electromagnetic force acting on the working side 4a of the focusing coil 4 and a heavy heart Between them. That is, always the deviation occurs between the one and the centroid of the working center point C ₄ and C ₅ of the electromagnetic force acting on the working edges 4a and 5a of each coil. Due to this shift, a rotational moment due to the electromagnetic force acts on the movable part, and the movable part is forced to swing unnecessarily. Such swinging of the movable portion is not preferable in maintaining accurate information reading, such as swinging the optical axis of the objective lens 1. In particular, when the electromagnetic force acts in a specific cycle, the swing is increased, and as a result, the information reading accuracy is reduced. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a lens driving device that can always accurately read information. In the lens driving device according to the present invention, the objective lens for irradiating the recording surface of the optical recording medium with the spot light, and the lens holder holding the objective lens are arranged in the direction of the optical axis of the objective lens and the direction perpendicular thereto. A lens driving device comprising: a supporting mechanism movably supporting the objective lens so that an optical axis of the objective lens is perpendicular to the recording surface; and driving means for applying a driving force to the objective lens and the lens holder. The driving unit includes a yoke having a magnet fixed only at one end of the opposing end thereof, a first coil wound so as to surround the one end of the yoke and the magnet, and a yoke. A second coil wound so as to surround the other end of the first coil and having a coil center axis in the same direction as the first coil;
The third coil has a coil center axis perpendicular to the coil center axis of each of the first and second coils, and has a working side sandwiched between the first coil and the second coil. Hereinafter, a lens driving device according to the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an objective lens constituting a lens driving device according to the present invention, a lens holder to which the objective lens is attached, and a driving means for driving these. As shown in FIG. 1, an objective lens 1 for irradiating a recording surface of a recording medium (not shown) with spot light is attached to a lens holder 2. The lens holder 2 is formed with a hollow part 3 penetrating therethrough. The hollow part 3 penetrates the lens holder 2 in the optical axis direction of the objective lens 1, for example. In the hollow portion 3, a focusing coil 24 whose coil central axis is parallel to the optical axis direction of the objective lens 1 and a tracking coil 25 whose coil central axis is perpendicular to the optical axis direction are fixed by, for example, an adhesive. As is apparent from FIG. 1, the focusing coil 24 and the tracking coil 25 in the lens driving device according to the present invention have the magnetic gap of the magnetic circuit composed of the magnet 8 and the yoke 9 when the current is supplied to each of the coils 24 and 25. Either the action side 24a of the objective lens 1 receiving the electromagnetic force in the optical axis direction (direction of arrow F) or the action side 25a of receiving the electromagnetic force in the direction of arrow T perpendicular to the optical axis direction in the objective lens 1 The side (24a in FIG. 1) is the other working side (first
In the figure, it is composed of two layers so as to sandwich 25a). To achieve such a configuration, each of the coils 24 and 25 shown in FIG.
24, the working side 25 of the tracking coil 25
It sandwiches a. If the focusing coil 24 and the tracking coil 25 configured as described above are fixed at four points in the hollow portion 3 of the lens holder 2 as shown in FIG.
Can be reinforced. FIGS. 3 (a) and 3 (b) show different models of the focusing coil 24 and the tracking coil 25 according to the present invention. FIG. 3 (a) shows a configuration in which the tracking coil 25 is sandwiched between the inner peripheral surface of the larger focusing coil 24b and the outer peripheral surface of the smaller focusing coil 24s. FIG. 3 (b) shows the focusing coil. FIG. 3 (c) shows a configuration in which the tracking coil 25 is sandwiched between the inside and the outside.
The configuration in which the tracking coil 25 shown in FIG. 3A is linked to the larger focusing coil 24b is provided inside the focusing coil 24 shown in FIG. 3B in FIG. 3D. The configuration shows that the tracking coil 25 is linked with the focusing coil 24. The configuration of the lens driving device according to the present invention is the same as that of the already-developed lens driving device shown in FIG. For details, refer to the above-mentioned “Background Art”. Effect of the Invention As described above, in the lens driving device according to the present invention, the driving means for driving the objective lens and the lens holder includes a yoke in which a magnet is fixed to one end of the opposing end thereof, A first coil wound so as to surround the magnet, a second coil wound so as to surround the other end of the yoke, and having a coil center axis in the same direction as the first coil; A third coil having a coil center axis perpendicular to the coil center axis of each of the first and second coils and having its working side sandwiched between the first and second coils; Therefore, the central point of action of the electromagnetic force acting on each action side can be integrated into a single point. If the center of gravity of the movable part consisting of the objective lens, each coil and the lens holder is made coincident with the integrated single working center point, the rotation that swings the movable part when the movable part is driven by the electromagnetic force The moment does not work, and accurate information reading is always possible. In addition, since the electromagnetic force no longer acts as the rotational moment, the electromagnetic force can be effectively used as a driving force for driving the objective lens and the lens holder, and a lens driving device with high operation efficiency can be obtained. It becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a configuration of an objective lens, a lens holder and a driving means of a lens driving device according to the present invention, and FIG. 2 is a view showing the objective lens, the lens holder and the driving means of FIG. FIG. 3 is a plan view showing the assembled portion, FIG. 3 is a diagram showing a model of a configuration example of each coil in the present invention, and FIG. 4 is a diagram showing an already developed lens driving device. Description of reference numerals of main parts 1 ... objective lens 2 ... lens holder 3 ... hollow part 6 ... support member 7 ... base 8 ... magnet 9 ... yoke 10 ... magnetic gap 24 ... Focusing coil according to the present invention 25: Tracking coil according to the present invention

Claims (1)

(57) [Rules for requesting registration of utility model] An objective lens for irradiating the recording surface of the optical recording medium with spot light; and a lens holder for holding the objective lens movably in an optical axis direction of the objective lens and in a direction perpendicular thereto. A lens driving device including: a support mechanism that supports an optical axis so as to be perpendicular to the recording surface; and a driving unit that applies a driving force to the objective lens and the lens holder. A yoke in which a magnet is fixed to only one end of the opposing end, a first coil wound to surround the one end of the yoke and the magnet, and a coil wound to surround the other end of the yoke A second coil that is turned and has its coil center axis in the same direction as the first coil; and a second coil that is perpendicular to the coil center axis of each of the first and second coils. A lens drive device comprising: a third coil having a coil center axis and having its working side sandwiched by each of the first coil and the second coil.