JPH0321972B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to 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 amount of 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 displacement caused by the rotational movement of the disk. It performs focus control to control the distance between the objective lens and the information track position in response to disc surface shake, and also performs time correction, ie, jitter control, necessary during video disc playback.

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 optical 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 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, since the objective lens is provided with an elastic member for tracking control and is driven in the focus direction including this elastic member, when the lens and the elastic member are driven in the focus direction with the elastic member tilted in the tracking direction,
There is a fatal problem in that the elastic action of the elastic member causes a time lag 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, and furthermore allows the objective lens to be controlled at 90 degrees in either the tracking direction or the focus direction. That is, even in the tangential direction of the information track, it is possible to perform time correction, that is, jitter control, which is necessary for reproducing a video disc, for example, and to improve the linearity of the operation in either direction.
The object of the present invention is to provide an objective lens driving device that has good linearity, has a simple structure, and is lightweight.

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 placed on the same axis with a certain space between them, as shown in Figure 1, and are magnetized in opposite directions on the same axis, with the two same poles facing each other. . Therefore, a common magnetic field is generated in the space between the two opposing permanent magnets 1 and 2. T shown in Figure 1
The three axes, the F axis, the F axis, and the Z axis, are perpendicular to each other, and here, the Z axis is the direction in which the two permanent magnets 1 and 2 are magnetized. The intersection of the three axes is assumed to be at the midpoint of the space where the two permanent magnets 1 and 2 face each other. In this space, the coil winding frame 3 is placed at T, F,
It is supported so as to be movable in any direction in each direction of Z (the support structure is not shown in FIG. 1),
At the outer periphery of this coil winding frame 3, a first coil 4 is arranged parallel to the F-Z plane, and a second coil 4 is arranged parallel to the Z-T plane.
A third coil 6 is wound within the coil 5 and the T-F plane. Note that each coil is assumed to have a rectangular shape.

Now, when a current flows in the direction of the arrow in the first coil 4 shown in FIG. 1, the coil winding frame 3 moves in the direction of the arrow on the T-axis due to the electromagnetic action between the first coil 4 and the permanent magnets 1 and 2. . Similarly, when a current is applied to the second coil 5 in the direction of the arrow, the coil winding frame 3 moves in the direction of the arrow on the F axis.
moves, and when a current is applied to the third coil 6 in the direction of the arrow, the coil winding frame 3 moves in the direction of the arrow on the Z-axis.
Of course, if the direction of current flow is reversed, the moving direction of the coil winding frame 3 will also be reversed. In reality, the coil winding frame 3 receives forces in various directions due to the electromagnetic action of the permanent magnets 1 and 2 and the coils wound in all directions. The force generated by electromagnetic action between the permanent magnets 1 and 2 is the most dominant.

That is, when current is supplied to each of the three coils wound in directions perpendicular to each other within one common magnetic field, the coil winding frame 3 receives a driving force and moves in a predetermined direction.

Next, specific examples of the present invention will be shown. A first embodiment of the present invention is shown in FIGS. 2 to 5.

This first embodiment shows an objective lens driving device for controlling the objective lens in two directions: tracking direction and focusing direction. The objective lens 7 is fixed to a holder 8 which also serves as a coil winding frame, and the holder 8 has a hole 8a through which the optical path from the objective lens 7 passes. A tracking control coil 9 is wound around the outer periphery of the holder 8 in parallel to the focus direction (F direction), and a focus control coil 10 is wound in a rectangular shape parallel to the tracking direction (T direction). One end of electrically conductive plate springs 11, 12, 13, 14 made of metal or the like is fixed to the upper and lower sides of the holder 8 to restrict movement in the tracking direction and the focusing direction. , 12, 13, and 14 are fixed to a support 15 at their other ends. This support 1
5 is fixed to the base 16. Thereby, the objective lens 7 is supported so as to be movable in any direction of the T direction and the F direction.

On the other hand, a holder 8 around which control coils 9 and 10 are wound
Permanent magnets 17 and 18 are fixed to the base 16 so that a constant air gap is formed with respect to the holder 8 in the front-rear direction, that is, in the direction perpendicular to the F-T plane. The magnetization directions of these permanent magnets 17 and 18 are coaxial and opposite as shown in FIGS. 2 and 3.

Here, details of the operation of the leaf springs 11, 12, 13, and 14 will be described.

FIG. 4 is a top view of the above embodiment, and FIG. 5 is a side view of the same. As mentioned above, one end of the mutually independent leaf springs 11, 12, 13, 14 is fixed to the holder 8 and the other end to the support 15, but these leaf springs 11, 12, 13, 14 are As shown in FIGS. 3 to 5, strip-shaped first surfaces 11a, 12a, 13a, and 14a formed in the center are provided at both longitudinal ends of the first surfaces 11a, 12a, 13a, and 14a. 2
It has surfaces 11b, 12b, 13b, and 14b.
and the vicinity of both ends of the first surfaces 11a to 14a and the first surfaces 11a to 1 of the second surfaces 11b to 14b.
Through-holes 11c to 14c are provided in portions close to 4a, respectively, to weaken these portions and to allow bending around these portions.

In this way, in FIG. 4, if a driving force in the T direction is now received, each bent portion (the bent portion near both ends of the first surfaces 11a to 14a as shown by arrows in FIG. 4) The objective lens 8 moves parallel to the support 15 in the T direction using the portion ) as a fulcrum. In addition, in FIG. 5, if a driving force in the F direction is now applied, each bent portion (second surface 11b to
14b near the first surfaces 11a to 14a (the part indicated by the arrow in FIG. 5) as a fulcrum,
The objective lens 8 moves parallel to the support 15 in the F direction.

Therefore, when such leaf springs 11 to 14 are used, the objective lens 8 can be moved in the tracking direction and the focus direction without giving an inclination angle to the optical axis while maintaining a parallel relationship with each other.

According to the above embodiment, two independent coils integrated with the objective lens are placed in one common magnetic field, and the objective lens is directly driven by applying current to these coils. can do. Therefore, there is no problem that a phase shift occurs with respect to the focus control signal when the tracking support spring is tilted, which occurs when the conventional focus control is controlled via the tracking support spring. Also 2 for control
Since only two independent coils are provided and there is no yoke system, linearity of movement is good, and by appropriately setting the permanent magnet and coil dimensions, the required range of movement can be extremely wide. . In addition, the structure is lightweight and extremely simple, so the response speed, frequency characteristics, phase characteristics,
Various characteristics such as drive efficiency are greatly improved.

By the way, since this embodiment is a moving coil type objective lens drive device, lead wires are required to supply control current to each coil 9 and 10, but in this embodiment, in order to prevent abnormal resonance of the lead wires, In addition, the four leaf springs 11, 12, 13, and 14 are commonly used as lead wires. That is, as shown in FIG. 2, the ends of each coil 9, 10 are connected to one end of the leaf springs 11, 12, 13, 14, and the lead wire 24 for applying a control current is connected to the other end, and the leaf spring 11,1
2, 13, and 14 are used as part of the lead wire.

In this way, even though it is a moving coil type, the plate spring can also be used as a lead wire for applying a control current, so there will be no resonance abnormality in the lead wire.

Next, a second embodiment of the present invention will be described with reference to FIGS. 6 and 7.

This second embodiment adds control of the jitter direction when used for video discs, and parts having the same functions as those of the first embodiment shown in Figs. 2 to 5 are given the same reference numerals. The explanation will be omitted, and the explanation will focus on the parts that are different from the first embodiment.

A tracking control coil 9 and a focus control coil 10 are wound around a holder 8 having an objective lens 7, as in the first embodiment.
A jitter control coil 19 is wound in parallel within the T plane. And leaf springs 11, 12, 13, 1
4 are fixed to the holder 8, and their other ends are fixed in parallel to each other in the vertical direction of the intermediate support 20, which is lightweight and rigid. This intermediate support 20
One end of the parallel springs 21 and 22 is fixed to two planes parallel to the front-rear direction, that is, the F-T plane, and the other end thereof is fixed to the support body 23. Note that this support 23 is fixed to the base 16.

In this way, the objective lens 7 is supported so that it can move in any direction without tilting its optical axis with respect to the mutually perpendicular directions F, T, and Z in FIG. Then, in the same way as in the first embodiment, tracking, focusing, and Jitter can be corrected in each direction.

According to the second embodiment, as in the first embodiment, since the structure is simple and based on a lightweight support structure, various characteristics such as response speed, frequency characteristics, phase characteristics, and linearity are improved. Improved performance
The objective lens can be directly driven in three directions: tracking, focus, and jitter without being affected by the elastic support.

In the above embodiment, the through holes 11c to 14c are provided when forming the bent portions of the leaf springs 11 to 14, but V-shaped cuts or the like may be provided instead of the through holes.

As described above, the present invention includes an objective lens that is movably arranged with respect to encoded information tracks provided on a disc-shaped recording medium and that projects a reading light spot onto the information tracks;
The magnetic flux in the direction perpendicular to the disguised plane is parallel to the disguised plane formed by the optical axis of the objective lens and the axis orthogonal to the optical axis, and is placed at a predetermined distance from the objective lens. a generated permanent magnet; at least two mutually independent coils wound in directions perpendicular to each other on a holder integrated with the objective lens and disposed within the magnetic field of the permanent magnet; and a base. and four mutually independent conductive elastic members each having one end fixed to the base and the other end fixed to the holder to support the objective lens movably in at least two axes orthogonal to each other. one end of two of the four support members is connected to both ends of one of the two coils, and one end of the other two support members is connected to the other end of the other coil. By connecting both ends of the coil and supplying an objective lens control current to each coil through the support member, each support member is bent by the current flowing through the two coils and the electromagnetic action of the permanent magnet, and the objective lens is Since the coils are driven in at least two axial directions orthogonal to each other, the objective lens can be directly driven by energizing the coils, and therefore the conventional focus control can be performed using a tracking support spring. When the tracking support spring is tilted, as in the case where the tracking support spring is controlled via the .

Additionally, by passing current through two independent coils within a common magnetic field of one permanent magnet, the objective lens can be driven in two axes orthogonal to each other, making it possible to miniaturize without the need for separate magnetic circuits. In addition, it is made of four mutually independent conductive elastic materials, one end of each of which is fixed to a base, and the other end of which is fixed to a holder, so that the objective lens can be moved in at least two axial directions perpendicular to each other. The objective lens drive device supports the objective lens with a support member and supplies control current to each coil by effectively utilizing each support member, so the objective lens drive device has a simple configuration and can stably support the objective lens. can be provided.

[Brief explanation of the drawing]

Fig. 1 is a perspective view for explaining the principle of the present invention, Figs. 2 and 3 are perspective views and exploded perspective views of the first embodiment of the invention, and Figs. 4 and 5 are illustrations of the above embodiment. Top and side views of the main parts of the example, Figures 6 and 7
The figures are a perspective view and an exploded perspective view of a second embodiment of the invention. 7... Objective lens, 8... Holder, 9, 10,
19... Coil, 11, 12, 13, 14... Leaf spring, 15, 23... Fixed support, 16... Base, 17, 18... Permanent magnet, 20... Intermediate support, 21, 22 ...Parallel spring, 24...Lead wire.

Claims (1)

[Claims] 1. An objective lens that is movably arranged with respect to an encoded information track provided on a recording medium on a disc and projects a reading light spot onto the information track, and an optical axis of the objective lens and a permanent magnet that is arranged parallel to a masquerade plane formed by two axes perpendicular to the optical axis and at a predetermined distance from the objective lens, and generates magnetic flux in a direction perpendicular to the masquerade plane; at least two mutually independent coils that are wound in directions perpendicular to each other on a holder integrated with the objective lens and arranged within the magnetic field of the permanent magnet;
It consists of a base and four mutually independent conductive elastic members, each having one end fixed to the base and the other end fixed to four end sides of the mutually opposing surfaces of the holder, so as to support the objective lens. a support member movably supported in at least two axial directions orthogonal to each other, one end of two of the four support members is connected to both ends of one of the two coils, and the other By connecting one end of the two supporting members to both ends of the other coil and supplying an objective lens control current to each coil through the supporting members, the current flowing through the two coils and the permanent magnet An objective lens driving device characterized in that each support member is bent by electromagnetic action to drive the objective lens in at least two axial directions perpendicular to each other.