JPS62154237A - Optical pickup actuator - Google Patents

Abstract

PURPOSE:To obtain an optical pickup actuator which is light in weight and also has a good frequency characteristic, by forming an objective lens holding plate to a lamellar structure by sticking a resin plate and a metallic plate together. CONSTITUTION:A cylindrical side plate 15 is formed by an outside cylindrical part 15a consisting of a resin and an inside cylindrical part 15b consisting of an aluminum alloy. For instance, when the objective lens holding plate 13 and the cylindrical side plate 15 are constituted by using polyamide, a mass of an external size becomes about 1.5g, and a secondary resonance frequency becomes about 6KHz, but in this way, when the objective lens holding plate 13 in which a magnetic path is not interlinked at the time of driving, and an influence is scarcely exerted on a magnetic field is formed by lamellar structure adhered with a steel plate 13 to the polyamide resin plate 13 from the upper and lower parts, the mass increases a little to 2.0g and the flexural regidity can be raised to about 20 times, and the secondary resonance can be raised to 13KHz or above.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a rotating pickup used for recording and reproducing various optical discs such as optical video disc players, compact digital audio disc players, still image disc file devices, etc. The present invention relates to a type of optical pickup actuator.

2. Description of the Related Art The structure of a conventional rotary optical pickup actuator will be described with reference to FIGS. 7, 8, and 9a. 7th
The figure is a plan view of the optical pickup actuator. FIG. 8 and FIG. 9 are both cross-sectional views of the optical pickup actuator, and the cross-sectional directions are changed by 900 degrees from each other. Reference numeral 1 designates an objective lens holding plate, on which an objective lens 2 is provided at a position eccentric from the central axis of rotation, and a cylindrical side plate 3 is located on the outer periphery of the objective lens holding plate 1'.

The support shaft 4 stands perpendicularly to the yoke 5, and is coupled to a bearing portion 6 provided in the center of the objective lens holding plate 1. The laser beam emitted from the semiconductor laser is focused by the objective lens 2 to form a beam spot and irradiate it onto the optical disc surface.
However, in order to obtain good recording and reproducing characteristics, the objective lens holding plate 1 rotates around the support shaft 4 for tracking operation, and slides in the axial direction for focusing operation. conduct. Tracking 1b works by detecting the deviation of the laser beam with respect to a predetermined recording track V2 so that the laser beam accurately traces the recording track, and rotating the objective lens 2 in the radial direction according to the detected output. This is done by servo control. On the other hand, the focusing operation is performed by a focus servo control that detects the deviation of the focus of the laser beam so that the recording track is located within the focal depth of the laser beam, and slides and displaces the objective lens 2 according to the detected output. .

The magnetic circuit for performing the focusing operation and one racking operation will be described below. A ring-shaped magnet 7 is attached to the outer circumference of the yoke 6, and an outer circumferential yoke 8 is attached thereon. The outer yoke 8 consists of a yoke wall 8a and a notch 8b, and 8a and 8b are divided into 900 parts in the circumferential direction, and two of them are located at symmetrical positions. Similarly, the yoke 6 is connected to the yoke wall 5.
The yoke 5 and the outer yoke 8 are arranged such that the yoke walls face each other with the notches. A magnetic circuit 9 is configured between the yoke wall 6a, the magnet 7, and the yoke wall 8a, and the yoke wall 6a and the yoke wall 8
The cylindrical side plate 3 is positioned so as to be rotatably displaceable in the magnetic gap 1Q between a. Further, a bearing portion 6 is inserted and supported by the support shaft 4 so as to be slidable in the axial direction of the support shaft 4, and is positioned in the magnetic circuit portion. Focusing coil 1
1 and the tracking coil 12 are mounted on the outer periphery of the cylindrical side plate 3. The focusing coil 11 is wound in the circumferential direction, and by passing a current through it, a force is applied to the coil in the direction of the rotational center axis. By changing the direction and magnitude of the current in accordance with the detection output obtained by detecting the deviation of the focal point of the laser beam with respect to the signal recording surface of the optical disk, the movement of the objective lens holding plate 1 in the direction of the rotation center axis is achieved. to perform focusing. The tracking coil 12 is wound into a rectangular shape and is attached to the focusing coil 11 on the outer periphery of the cylindrical side plate 3. As shown in FIG. 9, the tracking coil 12 is composed of portions 12a and 12b facing in the rotational center axis direction and portions 12C and 12d wound in the circumferential direction of the cylindrical surface of the cylindrical side plate 3. , half of the tracking coil 12 belongs to the magnetic gap 1o, and the other half belongs between the yoke and the notch of the outer yoke. When a current is applied to the coil, currents in opposite directions flow in the circumferential direction in the portion 12C312d of the tracking coil 12 wound in the circumferential direction of the cylindrical surface of the cylindrical side plate, and the magnetic circuit 9 generates forces in opposite directions. Because of this, their forces cancel each other out. A portion 12a of the tracking coil 12 located in the magnetic gap 1o receives a circumferential force from the magnetic circuit 9. In the part 12F, a direct current flows in the opposite direction to that in the part 12a, so the part 12a
The portion 12b is arranged in a notch where the magnetic circuit 9 is not provided so that the forces applied thereto are not canceled out. Generally, four tracking coils 12 are installed at substantially symmetrical positions, and the direction of the current is taken into consideration so that each coil receives a force in the same direction. Then, a drive current corresponding to the detection output obtained by detecting the deviation of the laser beam with respect to a predetermined recording track is applied to the tracking coil 12, and the objective lens 2 is displaced, thereby ensuring tracking of the laser beam with respect to the recording trunk.

Problems to be Solved by the Invention However, the above configuration has the following problems. For example, in the case of a rotary optical pickup actuator used in a compact disc player, the objective lens holding plate 1 is generally made of resin, has a diameter of about 16 to 20 inches, and a side plate length of 7 to 2 inches.
The thickness of the top plate is about 3 mm. However, in the objective lens holding plate 1 of such a size, the natural frequency of the structure consisting only of the holding plate 1 and the cylindrical side plate 3 is approximately 5 to eKHz, and the frequency characteristics of the actuator are also large at 5 to eKHz. There was a problem in that secondary resonance occurred. Although the effects of this secondary resonance can be barely avoided by using an IT phase compensation circuit or the like during playback of compact discs, it becomes a major problem in optical discs such as video discs and optical data files. In general, in optical discs where the disc rotation speed is higher and the disc size is larger than that of compact discs, the frequency characteristics of the actuator used for recording to playback are such that there is no secondary resonance or phase delay up to 10 KHz, and there is no phase delay up to 15 KHz. It is required that there be no large secondary resonance.

One method of increasing the frequency of secondary resonance is to reduce the diameter of the objective lens holding plate 1. FIG. 10 shows the relationship between the diameter of the objective lens holding plate and the secondary resonance frequency. 10th
As is clear from the figure, even if the diameter of the objective lens holding plate 1 is halved, the resonant frequency will increase by only 60%, and at most the current 6 KHz will become 9 KHz. 1
However, in reality, since the objective lens 2 and the bearing 6 are attached to the objective lens holding plate, it is difficult to make the diameter half that of the objective lens holding plate. Another method for increasing the secondary resonance frequency is to increase the total thickness of the objective lens holding plate 1 or the cylindrical training plate 3 to increase its rigidity. FIG. 11 shows the relationship between the thickness of the objective lens holding plate 1 and the secondary resonance frequency. As is clear from the figure, even if the thickness of the objective lens holding plate is doubled, the resonant frequency will be slightly less than doubled, that is, around 8 kHz. Furthermore, doubling the thickness of the objective lens holding plate also nearly doubles the weight of the objective lens holding plate, which significantly reduces the acceleration during focusing and tracking operations, and also reduces the external shape of the objective lens holding plate. This contradicts the development trend of pickup actuators, which are becoming larger and smaller and lighter. On the other hand, the material of the objective lens holding plate and the cylindrical side plate was changed to a material with a lower density, which resulted in weight reduction and two
Although it is possible to simultaneously improve the next resonance, light materials (such as resin) generally have low rigidity, and it is difficult to obtain a suitable material from a single material.

As described above, in the conventional rotary optical pickup actuator, it has been extremely difficult to simultaneously achieve weight reduction and improvement of secondary resonance without significantly changing its external shape.

In view of the above problems, the present invention provides an optical pickup actuator that is lightweight and has good frequency characteristics.

Means for Solving the Problems In order to solve the above problems, the present invention provides an objective lens holding plate that is rotatable around a rotation center axis and slidable in the axial direction of the rotation center axis; The objective lens holding plate is comprised of an objective lens provided on the objective lens holding plate at a position eccentric from the rotation center axis, and a means for driving the objective lens holding plate in the two directions, and the objective lens holding plate is It has a layered structure made by laminating a resin plate and a metal plate.

For production The effect of this technical means is as follows.

By making the objective lens holding plate a layered structure of a resin plate and a metal plate, for example, an objective lens holding plate with a plate thickness of 2.5 mm can be placed on both sides of a resin plate with a plate thickness of 0.2H. In the case of a structure in which steel plates are bonded together, the bending rigidity is greater than that of an aluminum objective lens holding plate with a thickness of 2.5 blades, and an improvement in rigidity can be achieved without sacrificing light weight. That is, generally, the rigidity of the objective lens holding plate is increased by the metal layer, and the secondary resonance frequency of the optical pickup actuator can be increased to 10 KHz or more. Further, by forming the cylindrical side plate with a layered structure of resin and metal layers or only with metal plates, the rigidity of the cylindrical side plate is increased, and the secondary resonance frequency of the original pickup actuator can be increased to around 15 KHz.

EXAMPLE A first example of the present invention will be described below with reference to the drawings.

FIG. 2 is an exploded perspective view showing the assembled state of an optical pickup actuator according to the first embodiment of the present invention, and FIG. 1 is a cross-sectional view of the assembled state, as seen from the X direction in FIG. 3 is a sectional view of FIG. 1 viewed from the y direction.

In FIGS. 1 to 3, 13 is an objective lens holding plate;
4 is an objective lens, and 15 is a cylindrical side plate that holds a coil for driving the objective lens on its outer periphery and is located on the outer periphery of the objective lens holding plate. The objective lens holding plate 13 is a resin 13
a and a steel plate 13b, and a cylindrical side plate 15
is formed by an outer cylinder part 16a made of resin and an inner cylinder part 15b made of aluminum alloy. When the objective lens holding plate 13 and the cylindrical side plate 15 are made of, for example, polyamideimide as in the conventional example, the objective lens holding plate 13
The mass of the outer dimensions of the cylindrical side plate 15, which had a plate thickness of 2.5 ant and an outer diameter of 20 mm, a plate thickness of 0.5 nm and a width of 6 ff, was about 1.5 mm, and the secondary resonance frequency was about 8 KHz.

On the other hand, as in the first embodiment, the objective lens holding plate 13 has magnetic paths that do not intersect during driving and is less affected by the magnetic field -1.
By creating a layered structure in which a polyamide-imide resin plate 13 with a plate thickness of 2.1 ff and a steel plate 13b with a plate thickness of 0.2 ff are laminated from above and below, the bending rigidity is increased by about 20 times with a slight increase in mass of 2.0 y. and the secondary resonance is 1
It can be increased to 3KHz or more. In addition, the above first
In this embodiment, the outer cylinder part 15a of the cylindrical side plate 15 is integrally formed with the objective lens holding plate 13 from polyamideimide, and the inner cylinder part 15b is formed from aluminum.

Since the inner cylindrical portion 15b is formed thin so as to have high electrical resistance, no eddy current is generated in the cylindrical side plate 15, and smooth driving of the objective lens 14 can be ensured. Therefore, the cylindrical side plate 15 can be driven with accurate phase together with the objective lens holding plate 13, and high-performance focus servo control can be maintained. 15a and an inner cylinder portion 1 formed of aluminum
By making it a composite of 5b, the rigidity of the cylindrical side plate is increased, and
We were able to achieve a significant improvement in the next resonant frequency.

1 to 3, 16 is a support shaft, 17 is a yoke, 18 is an outer yoke, 19 is a bearing portion, 26Vi magnet, 26 is a focus coil, and 27 is a tracking coil. In addition, FIG. 4 shows the objective lens holding plate 13.
FIG.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 6 is a sectional view of an objective lens holding plate and a cylindrical side plate of an optical pick amplifier actuator showing a second embodiment of the present invention. The objective lens holding plate 20 is formed from a polyamide-imide resin plate 20a, a steel plate 2ob, and an aluminum plate 20c.
It is integrally formed with the aluminum plate forming part a. Aluminum has a smaller Young's modulus than a steel plate, but also has a smaller specific gravity. Therefore, by increasing the thickness of the aluminum alloy layer on the objective lens holding plate, the overall mass can be greatly changed (the It is now possible to achieve the resonant frequency and actuator mass.

In the first embodiment, the resin plate 20a of the objective lens holding plate 20 was made of polyamide resin, but other resins may be used, and the metal plate 2zb was made of steel, but a metal with a ring B larger than that of the resin may be used. Alternatively, it may be a compound. Further, the inner cylinder portion 21b of the cylindrical side plate 21 may be made of an aluminum alloy. In addition, in the second embodiment, the aluminum plate 20c of the objective lens holding plate 20 and the inner cylinder part 21 of the cylindrical side plate 21
As shown in FIG. 6, the outer cylinder part 22a of the cylindrical side plate 22 is made of aluminum, the inner cylinder part 22b is made of resin, and a steel plate 23a is formed on the lower surface of the objective lens holding plate 23 on the upper surface. It goes without saying that the aluminum layer 23b may be integrally formed with the outer cylinder portion 22a by gluing the aluminum layers 23b together.

Effects of the Invention As described above, the present invention provides an objective lens holding plate that is rotatable around a rotational center axis and slidable in the axial direction of the rotational center axis, and the objective lens holding plate on the objective lens holding plate. An objective lens provided at a position eccentric from the rotation center axis, a coil for driving the objective lens holding plate in the two directions, and a cylindrical side plate holding the coil and located on the outer periphery of the lens holding plate. By making the objective lens holding plate have a layered structure of a metal plate and a resin plate, it is lightweight and easy to manufacture, and the secondary resonance frequency can be greatly increased, which has a great practical effect. There is.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an optical pickup actuator showing a first embodiment of the present invention, FIG. 2 is an exploded perspective view schematically showing an assembled state of the quaternary pickup actuator, and FIG.
1 is a sectional view taken along the line X--X of FIG. 2, whereas FIG. 4 is a sectional view taken along the y-y line of FIG. 2, and FIG. FIG. 5 is a sectional view of the objective lens holding plate and the cylindrical side plate in the second embodiment;
The figure is a sectional view showing another example of an objective lens holding plate and a cylindrical side plate, FIG. 7 is a plan view of a conventional optical big amplifier actuator, FIG. 8 is a sectional view of FIG. 7, and FIG. The cross-sectional view of FIG. 7 shows a cross section orthogonal to the cross section of FIG. 8. Figure 9 is a perspective view of the tracking coil in Figure 7;
Figure 0 shows the relationship between the diameter of the objective lens holding plate and the secondary resonance frequency.
FIG. 11 is a diagram showing the relationship between the thickness of the objective lens holding plate and the secondary resonance frequency. 13.20,23...χ・1 object lens holding plate, 1
5゜21. 22...Cylindrical III Oi, 26
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Claims (2)

[Claims] (1) An objective lens holding plate that is rotatable in a direction around a rotational center axis and slidable in an axial direction of the rotational center axis, and an objective lens holding plate that is eccentric from the rotational center axis on the objective lens holding plate. an objective lens provided at a position, a tracking coil for rotationally driving the objective lens holding plate in a direction around the rotational center axis, and a tracking coil for driving the objective lens holding plate in an axial direction of the rotational center axis. and a cylindrical side plate that holds the tracking coil and the focusing coil and is located on the outer periphery of the lens holding plate, and the objective lens holding plate has a layered structure of a metal plate and a resin plate. An optical pickup actuator characterized by: (2) The optical pickup actuator according to claim 1, wherein the cylindrical side plate has a layered structure of a metal plate and a resin plate.