JPH0140407B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a reproducing apparatus that optically reads information by projecting a light spot onto an information track in which a high-density digital signal is recorded on a disc-shaped recording medium. The present invention relates to an objective lens driving device that controls the position of an objective lens relative to a disk surface in order to accurately correct and control the position of a light spot with respect to an information track signal.

More specifically, for example, tracking control corrects the eccentricity of the information track with respect to the center of rotation of the disk, that is, the relative positional deviation in the radial direction of the disk, and the warpage of the disk itself and the relative deviation caused by the rotational movement of the disk. Focus control is performed to control the distance between the objective lens and the information track position in response to the vibration of the disk surface.

Generally, this type of optical information reading device is used in video disks that record video signals and digital audio disks that record encoded audio signals, as well as in other high-density information recording and reproducing devices such as those related to computers. It is applied.

This involves recording encoded video signals, audio signals, and various other information on a disk as information tracks, and then rotating the disk at high speed while directing light emitted from a light source such as a laser beam onto the disk. The original recorded information is reproduced by focusing the light onto the information track of the disk and reading the reflected light from the disk surface.

This optical information reading device can record information at an extremely high density, and has the advantage of being able to record information at a higher density, with higher accuracy, and with higher performance than conventional analog systems.

On the other hand, since the width and pitch of the information track are extremely small, in order to faithfully reproduce this high-density information, the focusing diameter of the light spot for reading must also be extremely small. In order for the light spot to accurately follow the information track on the disk, there is a problem in that the objective lens must be accurately driven and controlled so that no relative positional deviation with the disk occurs.

In order to solve this problem, conventional methods have been used to electrically detect the reflected light from the disk surface and control the reading light spot position to match the information track position.

One example is a method in which a rotatable mirror is placed in the optical path between the laser beam and the objective lens, and the mirror is rotated and controlled based on the information of the tracking error signal. However, this method has the drawback that a certain inclination angle always occurs in the optical axis within the objective lens, and highly accurate reproduction cannot be expected.

As another example, the objective lens or its holding frame is supported by an elastic support member made of a leaf spring, and tracking control is performed by displacing the objective lens parallel to the disk surface according to a tracking error signal. The entire device including the elastic support member, the objective lens, and the drive device for tracking control is supported by another elastic support member, and this is connected to the drive device for focus control (for example, a voice coil commonly used in speakers). A method has been proposed in which the focus is controlled by driving the objective lens in a direction perpendicular to the disk surface. However, in this method, tracking control and focus control are performed by separate electromagnetic devices, so the configuration is complicated.
There is also a problem that the weight increases and the response at high frequencies deteriorates. Moreover, the objective lens is provided with an elastic member for tracking control, and since the elastic member including this elastic member is driven in the focus direction, when the elastic member is inclined in the tracking direction, the elastic action of the objective lens and the elastic member is used. There is a problem in that a temporal and phase shift occurs in the movement of the lens in the focus direction, making accurate focus control impossible.

The present invention eliminates these drawbacks, enables more accurate control of the objective lens in the tracking direction and the focus direction, has good linearity of operation in both directions, and has a simple structure. The present invention provides a lightweight objective lens driving device.

Hereinafter, details of the present invention will be explained with reference to the drawings.

FIG. 1 shows the principle for obtaining the driving force for driving the objective lens of the present invention. Two permanent magnets 1 coaxially arranged with a certain space between them
and 2 are coaxially magnetized in opposite directions as shown in FIG. 1, and form a magnetic gap with magnetic material yokes 3 and 4 each formed in a U-shape. On the other hand, coils 5 and 6 are wound around the movable part so as to cross each other at a certain angle. The two magnetic gaps mentioned above are arranged symmetrically with respect to the area where the two coils 5 and 6 cross. FIG. 2 is a diagram illustrating the direction of the driving force. For the sake of simplicity, only one direction in which the coils are in a crossed state will be explained. Now coil 5
When a current in a certain direction is passed through the coil 6, forces are generated in the directions of vectors a→ and b→, and the resultant force is V→. Furthermore, when only the direction of the current in the coil 5 is reversed, the vector c→ caused by the coil 5 and the vector b→ caused by the coil 6 result in a combined vector of H→. That is, by controlling the direction of the current flowing through the coils 5 and 6, it is possible to move the movable part in any vertical or horizontal direction.

FIGS. 3 and 4 show an embodiment of the present invention, and show a two-dimensional objective lens drive device in the tracking direction and the focus direction.

An objective lens 7 through which an optical signal passes is fixed in a center hole 8a of a holding member 8 which also serves as a coil winding frame. The holding member 8 is made of a lightweight and strong material, such as a light metal such as aluminum or magnesium, or a reinforced plastic containing a reinforcing agent such as carbon wire or glass, and is supported as shown in FIG. It has protrusions 9 and 10 for coupling with other members. Two coils 5 and 6 are wound symmetrically around the outer circumferential portion of the holding member 8 so as to surround the optical axis of the objective lens 7 and avoid the optical axis at a certain angle to each other.

Support members 11 and 12 for regulating two-dimensional movement are coupled to the distal ends of the coupling protrusions 9 and 10.

The support member 11 includes a parallelogram frame-shaped body consisting of a pair of elastic surfaces 13 and 14 and integral rigid surfaces 15 and 16, a pair of elastic surfaces 17 and 18, and a pair of rigid surfaces 1.
It is constructed by connecting parallelogram frame-like bodies consisting of 5 and 19 pieces. The support member 12 is similarly configured. That is, these supporting members 1
1 and 12 are adjacent elastic surfaces 13 and 17 and 1
It consists of two springs formed so that the angles 4 and 18 are at approximately 90 degrees.

These support members 11, 12 have rigid surfaces 16,
16 to the coupling protrusions 9 and 10 of the holding member 8, and by fixing the rigid surfaces 19 and 19 to the outer case 21, the holding member 8 is movably supported within the outer case 21.

The magnetic circuit consists of a U-shaped yoke 2 made of magnetic material.
One end 22a, 23a of 2, 23, magnets 24, 2 coaxially magnetized in opposite directions as shown in FIG.
5 is fixed, and the other shaft 22 of the yokes 22, 23
b, 23b are loosely fitted into the through holes 8b, 8b of the holding member 8, and the magnets 24, 25 are inserted into the coils 5, 6.
The yokes 22 and 23 are fixed to the outer case 21 with screws 26 and 27 in this state.

In this way, by passing a predetermined current through the coils 5 and 6, the holding member 8 is driven in the tracking direction and the focusing direction according to the operating principle shown in FIG. At this time, supporting members 11, 12
are rigid surfaces 15, 16, 1 constituting each parallelogram
9 moves in the tracking T direction and the focusing F direction shown in FIG. 3 by the elastic action of the elastic surfaces 13, 14, 17, and 18 while maintaining verticality with respect to the holding member 8 and the outer case 21. Therefore, the holding member 8 can be moved in two axes directions of tracking T and focusing F using the common supporting members 11 and 12, and when the holding member 8 is moved, the objective lens 8 can be moved.
The optical axis will not tilt.

The support members 11 and 12 are integrally molded from a synthetic resin having high elasticity such as polyimide or polypropylene, and the elastic surfaces 13, 14, 17, and 18 are thin walls, and the rigid surfaces 16 and 19 are thick walls. be able to. Of course, the elastic surfaces 13, 14, 17, 1
8 and the rigid surfaces 16 and 19 may be made of different materials, and these may be bonded with an adhesive, or may be integrated by inserting, outsert, etc. inside a molding die.

Furthermore, although the embodiments shown in FIGS. 3 and 4 are constructed by connecting two parallelogram frame bodies, it may be constructed by connecting three or more parallelogram frame bodies.

Furthermore, in the embodiments shown in FIGS. 3 and 4, the supporting members 11 and 12 are arranged in parallel in order to downsize the entire device, but these supporting members 11 and 12 are arranged in parallel.
The holding member 8 may be arranged coaxially on the O-O' axis in the figure, and the holding member 8 may be held between the rigid surfaces 16, 16 of the respective supporting members 11, 12.

5 and 6 show the transmission characteristics in the tracking direction and focus direction according to the above embodiment.

As described above, the present invention provides two
The electromagnetic action of the current flowing through each coil and the magnetic force of the magnet and yoke placed opposite the two coils generates a driving force in each coil, and the combined driving force of these driving forces generates a driving force. The holding member is driven in at least two axial directions. In this way, since the holding member can be directly driven by the coil wound around the holding member, the phase characteristics of the objective lens attached to the holding member can be made extremely excellent.
In addition, since a common magnetic gap is used for the two axes,
There is no imbalance in each axis direction, and all frequency characteristics are stable and excellent. Furthermore, since the magnetic gap is directly formed by the magnet and the yoke, the configuration of the magnetic circuit is simple and the magnetic efficiency can be improved.

[Brief explanation of drawings]

1 and 2 are an exploded perspective view and an operation explanatory diagram showing the principle of the present invention, FIGS. 3 and 4 are a fragmentary perspective view and an exploded perspective view of essential parts of an embodiment of the present invention, and FIG.
6 are transfer characteristic diagrams of the above embodiment. 5, 6... Coil, 7... Objective lens, 8...
Holding member, 9, 10... Connection protrusion, 11, 1
2... Support member, 13, 14, 17, 18... Elastic surface, 16, 15, 19... Rigid surface, 21... Outer case, 22, 23... Yoke, 24, 25...
Magnet.

Claims (1)

[Claims] 1. A holding member movably disposed facing the encoded information track provided on a disc-shaped recording medium, an objective lens attached to this holding member, and a holding member attached at a predetermined angle to the holding member. It is equipped with two coils wound so as to cross each other, and a magnet and a yoke arranged with a predetermined gap at a position facing the crossing portion of the two coils, and between the magnet and the yoke. A driving force is generated in each of the coils through the electromagnetic action of a magnetic force and a current flowing through each of the coils, and the holding member is driven in at least two axial directions by a combined driving force that is a combination of the driving forces generated in each of the coils. An objective lens driving device characterized in that: