JPH038129A - Objective lens driving device - Google Patents

Abstract

PURPOSE:To reduce heating of a driving coil and the power consumption by driving an objective lens moving body by a first driving means against a small deformation of a disk and driving integrally the moving body and a supporting body by a second driving means against a large deformation. CONSTITUTION:In the case of reproducing a disk of a small deformation, a driving coil 4b is brought to electric conduction and by a permanent magnet 8 and a yoke 1a, a moving body 2 is moved minutely in the diameter direction of the disk. Also, a coil 4a is brought to electric conduction and the moving body 2 is moved minutely in the optical axis direction of an objective lens 3. On the other hand, against a large deformation, an ultrasonic motor is driven by an error current flowing through the coil 4a. As for a rotor 11 of this motor, a cam groove 11a of the outside peripheral part is engaged to a guide pin 7 and the moving body 2 is moved in the optical axis direction together with a supporting body 6. In such a way, by moving the objective lens by a first or a second driving means in accordance with a size of the deformation of the disk, heating of the driving coil is suppressed and the power consumption is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pickup for recording and reproducing various optical discs, such as an optical video disc player, an optical digital data disc device, etc., and particularly relates to a pickup for driving an objective lens thereof. This relates to a drive device.

BACKGROUND OF THE INVENTION Recently, optical discs that record video and audio on both sides are becoming increasingly popular. Video optical discs currently in use have a diameter of 20 cm to 30 cm. Additionally, digital information is recorded optically.

So-called optical digital data discs for playback are also becoming popular mainly for industrial use, but in this case too, the diameter is 30 cm.
Many of them are around m. These discs are not necessarily used in a fixed usage environment, and video optical discs in particular are used in general households, so their temperature and humidity environments are extremely wide. As mentioned above, a disk with a large diameter of about 30 cm is easily affected by temperature and humidity. For example, if it is left in a high temperature and humid environment for a long time, the amount of deformation (warpage) of the disk can be several mm. It can also extend. Whether or not a disk with such deformation can be used depends largely on the performance of the pickup.

Generally, when picking up an optical disc, it is necessary to move the objective lens minutely in a direction perpendicular to the track (in the radial direction of the disc) in order to perform tracking control that allows the laser beam to accurately follow the track on the desired track. At the same time, it is necessary to minutely change the distance between the disk and the objective lens in order to perform focusing control to optimize the spot diameter of the laser beam on the track. An objective lens driving device for driving such an objective lens in two directions includes a semiconductor laser,
It is configured as a block separate from the so-called optical system block, such as a photodiode and a beam splitter.

As an example of an objective lens driving device in a conventional pickup, Japanese Patent Laid-Open No. 59-221839 discloses a bobbin to which an objective lens is attached is supported by four parallel metal wires processed straight. Now, let us consider a case where focusing control is performed by this objective lens driving device.

When a focus error signal is detected, a driving coil is energized in response to this, and the objective lens moves in the direction of its optical axis under the driving force. At this time, the bobbin receives a resistance force from the metal wire corresponding to the amount of movement of the bobbin. As the amount of movement increases, the above-mentioned resistance increases, so in order to overcome this, the current flowing through the drive coil must also increase. In the case of a digital audio disc with a diameter of about 12 cm where the driving range of the objective lens is not so wide (i.e., the amount of disc deformation is small), the above-mentioned resistance force is negligible.

Problems to be Solved by the Invention However, when attempting to drive the objective lens in response to a large amount of deformation such as the above-described disk with a diameter of about 30 cm, the amount of movement required for the objective lens becomes considerably large. Therefore, the amount of current supplied to the drive coil also increases, resulting in the problem of heat generation in the coil.

In particular, since the deformation of the disk generally increases gradually from the inner circumference to the outer circumference of the disk, if the pickup is located at the outer circumference of the disk, a large current will continue to flow through the drive coil. There were problems not only in terms of heat generation in the drive coil but also in terms of power consumption.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide an objective lens drive device that can suppress heat generation of a drive coil and minimize the energy used to drive the drive coil.

Means for Solving the Problems In order to solve the above problems, the objective lens drive device of the present invention includes a movable body supported movably in the optical axis direction of the objective lens while holding the objective lens; a first driving means comprising a driving coil fixed to the moving body, a permanent magnet disposed opposite to the driving coil, and a fixed yoke for supporting the permanent magnet; and a first driving means capable of freely moving the moving body. a support body disposed to be movable relative to the fixed yoke in the optical axis direction of the objective lens, and a second driving means for driving the support body. .

Effect With the above configuration, the moving body holding the objective lens is driven by the first driving means to follow a small deformation of the disk, and the movable body holding the objective lens is driven to follow a small deformation of the disk. The movable body and the support body supporting the movable body are driven together by the second driving means.

Practical Examples The present invention is particularly effective against deformation of disks with large diameters, and is based on the premise that the deformation of the disk is generally gradually increased from the inner circumference to the outer circumference of the disk. The fact is that the change in the amount of deformation is not so rapid but rather gradual, and that the manner of deformation is continuous rather than sudden. Therefore, a great deal of ingenuity is required to deal with, for example, changes corresponding to the rotation period of the disk, or localized protrusions or depressions on the disk surface due to some reason. However, the sudden large deformation (the amount of deformation is 1
(up to 3 mm) is highly unlikely, and most rapid and small deformations can be handled by conventional objective lens drive devices.

The present invention was made based on the above background,
The structure of one embodiment will be described below with reference to the drawings.

FIG. 1 is an exploded perspective view of the objective lens driving device of the present invention, FIG. 2 is a front view thereof, and FIG. 3 is a side view thereof.

The fixed yoke r is made of a material that easily passes magnetic flux (high magnetic permeability), and is a base having two protrusions on one side, and a permanent magnet 8 is fixed inside each protrusion. There is.

On the fixed yoke 1, there is a cylindrical yoke 1a which has a through hole at its center, is formed integrally with the fixed yoke 1, and is arranged at the center position between the two permanent magnets 8. Fixed yoke 1
．． A closed magnetic path is configured by the permanent magnet 8 and the yoke 1a.

Reference numeral 2 denotes a cylindrical moving body, on the outer periphery of which drive coils 4a and 4b are provided, and on one end of which an objective lens 3 is fixed. Drive coil 4
a is wound around the outer periphery of the movable body 2, and a driving coil 4
b is wound across a pair of protrusions 2a provided to protrude in the radial direction of the movable body 2. The movable body 2 includes a yoke 1a in a hollow portion thereof, and drive coils 4a and 4b are disposed in a closed magnetic path facing the permanent magnet 8 (first drive means).

Reference numeral 5 denotes a linear elastic member having a predetermined elastic coefficient and damping coefficient, each of which has one end fixed to the protrusion 2a and the other end fixed to the support body 6. All four linear elastic members 5 have the same length, are arranged parallel to each other, and support the movable body 2 so as to be movable in the directions of arrows A and B.

The support body 6 is a gate-shaped member provided with two through holes 6a, and two guide rods 9 planted on the tongue-shaped portion 1b of the fixed yoke 1 are slidably engaged with the through holes 6a. are doing. Further, a guide bin 7 is installed on the inner surface of one columnar portion 6b of the support body 6.

An ultrasonic motor (second driving means) consisting of a stator 10 and a rotor 11 is arranged on the lower surface of the tongue-shaped portion 6 of the fixed yoke 1. The stator 10 includes an elastic body, a piezoelectric element, etc.
(not shown) and is fixed to the fixed yoke 1. The rotor 11 has a cam groove 11a formed in its outer periphery, and rotates around a rotating shaft flb engaged with the stator 10. The structure and operation of this ultrasonic motor are as follows:
For example, National Technical Rep.
ort (vol, 33 No, 5 Oct, +987), etc., so the explanation here will be omitted. A guide pin 7 is engaged with the cam groove 11a.

Next, its operation will be explained. When reproducing a disc without significant deformation, the objective lens drive device of the present invention operates in the same way as a conventional objective lens drive device. That is, when tracking control is performed to cause the laser beam to accurately follow a desired track on the disk, when a tracking error signal is detected, the driving coil 4b is energized. Since the driving coil 4b is in a closed magnetic path formed by the permanent magnet 8 and the yoke 1a, it receives a driving force and moves minutely in the radial direction of the disk (in the direction of arrow B) together with the moving body 2. At this time, the movable body 2 moves horizontally while being supported by the linear elastic member 5, and the inclination of the optical axis of the objective lens 3 is suppressed to a minimum. In addition, when performing focusing control to optimize the spot diameter of the laser beam on the track, when a focus error signal is detected, the drive coil 4
A is energized. The driving coil 4a is also the driving coil 4b.
Similarly, the movable body 2 receives a driving force and moves slightly in the optical axis direction of the objective lens 3 (in the direction of arrow A).

In this case as well, the inclination of the optical axis as the moving body 2 moves is minimized.

On the other hand, when reproducing a disk with large deformation, the current flowing through the drive coil 4a increases in proportion to the amount of deformation, resulting in a steady error current. This steady-state error current is applied to a drive circuit (not shown) to drive the above-mentioned ultrasonic motor. Cam groove 11a on the outer periphery of the rotor 11 of the ultrasonic motor
A guide bin 7 is engaged with the rotor 11, and as the rotor 11 rotates, the guide bin 7 moves together with the support 6 in the direction of arrow A, that is, in the optical axis direction of the objective lens 3. The movable body 2 holding the objective lens 3 moves together with the support 6 and follows the large deformation of the disk.

Of course, the above-mentioned disk does not only undergo large deformations, but also small (microscopic) deformations superimposed on this.

In addition, the influence of surface runout during rotation of the disk is large, and corresponds to a small deformation in this case.

These deformations change over time while the disk rotates, and large deformations change quickly (there are only low frequency components), but the smaller the deformation, the faster the change. The speed is high (there are high frequency components). In the objective lens driving device of this embodiment, large deformations that are low frequency components are followed by the movement of the support 6, but at the same time, small deformations that are high frequency components are followed by the drive coil 4a. It follows with minute movements. For a disk with such large deformation, focusing control of the objective lens is achieved by the cooperative operation of the support body 6 and the movable body 2.

Further, in this embodiment, an ultrasonic motor was used as a driving means (second driving means) for the support body 6. This is because the fundamental characteristics of the ultrasonic motor are that it is self-retaining when not driven, is not affected by external magnetic fields, and can obtain high torque at extremely low speed rotation.

First, the self-retention property when not driven is obtained because the torque generation principle of the ultrasonic motor is friction, and even when disturbance torque is applied, the rotor 11
Since the support body 6 is held without being rotated, energy (current) for holding it is not consumed even when the support body 6 is not moved.

Next, the ultrasonic motor uses piezoelectric elements,
Since it is not a motor that uses magnetic force, it will not be affected by strong magnetic fields. Therefore fixed yoke 1
Since it can be used in close contact with the members constituting the magnetic path, a compact configuration can be realized without any restrictions on configuration.

Furthermore, since ultrasonic motors can basically provide high torque at extremely low speeds, no speed reduction mechanism is required.

Although the means for driving the support body 6 is not limited to an ultrasonic motor, the ultrasonic motor is one of the most suitable for the objective lens driving device of the present invention due to the numerous advantages described above.

Effects of the Invention As is clear from the above description, the objective lens driving device of the present invention, when dealing with a large deformation of the disk, uses the first driving means that drives the driving coil fixed to the movable body to By driving the movable body and driving the movable body holding the objective lens and the supporting body that supports it together by the second driving means, the disk can be moved without passing a large current through the drive coil. Since it follows the deformation, not only can heat generation from the drive coil be suppressed, but also the energy required for drive can be minimized.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of an embodiment of the objective lens driving device of the present invention, FIG. 2 is a front view of the same, and FIG. 3 is a side view of the same. 1... Fixed yoke, 2... Moving body, 3...
・Objective lens, 4a, 4b... drive coil,
5... Linear elastic member, 6... Support body, 7
...Guide pin, 8...Permanent magnet, 9...Guide rod, 10...Stator, 11...
Rotor, 11a... cam groove.

Claims (1)

[Scope of Claims] A moving body supported movably in the optical axis direction of the objective lens while holding an objective lens, a driving coil fixed to the moving body, and a driving coil facing the driving coil. a first driving means comprising a permanent magnet arranged therein and a fixed yoke for supporting the permanent magnet; An objective lens driving device comprising: a support body arranged to be relatively movable; and a second drive means for driving the support body.