JPS6349294B2 - - 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 high-density digital signals are 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.

In more detail, for example, the eccentricity of the information track with respect to the center of rotation of the disk, that is, the tracking control that corrects the relative positional deviation in the radial direction of the disk, the warp of the disk itself, and the relative positional deviation of the disk relative to 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 that occurs.

Generally, this type of optical information reading device is used in video discs that record video signals and digital audio discs that record encoded audio signals, as well as 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 light source 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 disadvantage that a certain tilt angle always occurs in the optical axis within the objective lens, making it impossible to achieve high-density reproduction.

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, the tracking control and focus control are performed separately using electromagnetic devices, which results in a complicated configuration.
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 a principle diagram for obtaining the driving force for driving the objective lens of the present invention. Two permanent magnets 1 and 2 are coaxially arranged with a certain space between them, and are magnetized in opposite directions on the same axis, as shown in Figure 1, and each has a U-shaped magnetic field. The material yokes 3 and 4 each form a magnetic gap. 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 2
The two coils 5 and 6 are arranged symmetrically with respect to the cross state. 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, when a current in a certain direction is passed through the coils 5 and 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 a pair of 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.
At one end 22a, 23a of 2, 23, there are magnets 24, which are coaxial and magnetized in opposite directions, as shown in FIG.
25 and the other end 22 of the yokes 22 and 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 the two axis directions of tracking T and focusing F using the common supporting members 11 and 12, and therefore the optical axis of the objective lens 7 will not be tilted during the movement.

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 support members 11 and 12 are arranged in parallel in order to downsize the entire device, but these support 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, 6, and 7 conceptually show the relationship between the supporting members 11, 12 and the holding member 8 in this case. When the holding member 8 is not driven,
As shown in FIG.
The holding member 8 is positioned at the center in a moderately bent state. When a driving force in the tracking T direction is applied to the holding member 8 in this state, the rigid surface 15 of the supporting member 11 sinks vertically, and the elastic surfaces 13, 1
4, 17, and 18 are bent downward. In addition, in response to this, the rigid surface 15 of the support member 12 is pulled up vertically, and the elastic surfaces 13, 14, 17, and 18 are extended nearly horizontally. This causes the holding member 8 to move in parallel in the tracking T direction. Next holding member 8
When a driving force is applied in the focus direction, the rigid surfaces 15, 15 of the support members 11, 12 are both pulled up in the vertical direction, the elastic surfaces 13, 14 are tilted, and the holding member 8 is translated in the downward focus direction. .
Movement of T and F in the opposite direction is performed in the same manner.

Reference numeral 29 shown in FIG. 4 indicates a counterweight for adjusting the center of gravity position of the holding member 8. The tracking and focus direction transmission characteristics without this counterweight 29 are shown in Figures 8 and 9.
As shown in the figure, abnormal peaks and dips occur in all directions, and a delay also occurs in the phase characteristics. This is because torsional resonance occurs due to the misalignment between the center of gravity of the holding member 8 and the driving point. On the other hand, when the counterweight 29 is attached and the center of gravity of the holding member 8 and the drive point are made to match, FIGS.
As shown in the figure, there is no abnormal resonance and extremely good characteristics are obtained.

In general, in this type of driving device, in order to form an electromagnetic driving device in which an objective lens with a short focal length is mounted close to the disk and a predetermined driving force is obtained, a counterweight 29 is used as described above.
It is extremely effective to adjust the center of gravity position of the holding member 8 using.

As described above, in the present invention, the holding member is provided with a counterweight, and the counterweight aligns the center of gravity of the holding member with the drive point. Therefore, the center of gravity of the holding member and the drive point are aligned. Torsional resonance due to misalignment can be prevented and extremely good transmission characteristics can be obtained.

[Brief explanation of the drawing]

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.
7 to 7 are conceptual diagrams for explaining the operation of the embodiment of the present invention, FIGS. 8, 9, 10, and 11.
The figure shows the transfer characteristics without and with a counterweight. 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, 29...Counterweight.

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. Two coils are wound so as to cross each other, a magnet is placed at a position facing the crossing portion of the two coils with a predetermined gap, and both ends are attached to the holding member and the fixing member, respectively. fixed,
At least two orthogonal to the information track
It includes a support member that bends in the axial direction and a counterweight for adjusting the center of gravity position of the holding member, and generates a driving force in each of the coils by the electromagnetic action of the magnetic force of the magnet and the current flowing in each of the coils. , the holding member is configured to be driven in two axial directions in which the supporting member is bent by a combined driving force obtained by combining the driving forces generated in each of the coils, and the center of gravity of the holding member and the driving force are adjusted by the counterweight. An objective lens driving device characterized in that points are made to coincide.