JP2700005B2 - Objective lens drive - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an objective lens driving device in an optical pickup used for an optical disk device or the like.

(Prior Art) In an optical disk device using an optical disk as a recording medium, an optical pickup is used to write and read information signals to and from the disk. In this optical pickup, it is necessary to accurately focus a laser beam on information pits of a disk. Therefore, an objective lens driving device that drives the objective lens in the direction of the optical axis in response to the shake or swing of the disk is used. Various characteristics required of the objective lens driving device include (1) high sensitivity, (2) excellent dynamic characteristics such as high-range tracking capability,
(3) Small size, (4) Low cost, etc.

11 to 17 show various examples of a conventional objective lens driving device.

In the example of FIG. 11, the objective lens 12 is attached to a lens holder 11 that is rotatable about the axis 16 and movable in the direction of the axis 16,
A focusing drive coil 15b is wound around the outer periphery of the lens holder 11 in a cylindrical shape, and further, four quadrangular tracking drive coils 15a are fixed to the outer periphery thereof. One side of each tracking drive coil 15a has inner and outer cores 13, It is arranged so as to be located in a magnetic circuit including 18.

In the example shown in FIG. 12, the objective lens 22 is mounted on a lens holder 21 which is rotatable about a shaft 26 and is movable in the direction of the shaft 26. Attach the drive coil 25b,
5b, two square tracking drive coils 25a are attached to the outer surface, and one side of each coil 25a has inner and outer cores 23,
It is arranged so as to be located in a magnetic circuit including the magnet 28 and the magnet 27.

13 to 15 show a quadrangular prism-shaped lens holder.
Attach the objective lens 32 in the center of 31 and focus driving coils 35 in the form of square tubes on both sides parallel to each other.
b, and a coil for tracking drive formed by bending a rectangular coil as shown in FIG. 14 into a U-shape so as to surround about half of the outside of each coil 35b.
The lens holder 31 is mounted so that the lens holder 31 can be moved by a parallel spring 34 in the optical axis direction of the objective lens 32 and in a direction perpendicular thereto. The magnetic circuit is composed of a yoke 33 having projections 33a, 33c on both sides and a central projection 33b as shown in FIG. 15, and a magnet 38 fixed to each inner surface of the projections 33a, 33c of the yoke 33. , The central projection 33
b is located at the center of the coil 35b, and the magnetic flux crosses each two sides of the coils 35b and 35a.

FIGS. 16 and 17 show an example of a rotatable and
The objective lens 42 is mounted on a lens holder 41 movable along 46, and a tracking drive coil 45a is mounted on each side, and a shaft 46 is provided below the coil 45a.
Cylindrical drive coil for focusing
45b is attached. A tracking magnetic circuit 43 is formed by a core and a magnet arranged to face the coil 45a, and a focusing magnetic circuit 48 is formed by a core and a magnet arranged to face the coil 45b.

(Problems to be Solved by the Invention) FIGS. 18 (A) to 18 (D) show the utilization efficiency of the focus drive coil and the tracking drive coil in the above-mentioned conventional objective lens drive device, that is, with respect to the total winding length of the coil. Indicates the ratio of the length of the portion where thrust works effectively. 18th
As is apparent from FIGS. 11A to 11C, according to the three conventional examples shown in FIGS. 11 to 15, the utilization efficiency is low because the ratio of the portion where the driving force is effectively generated in each coil is low. And the sensitivity is low. In these examples, the drive coils for focusing and tracking are overlapped and wound in the magnetic gap to share a common magnet, so that at first glance it seems to be suitable for high efficiency. However, in practice, since the coil is wrapped around the coil, the magnetic gap is widened and the magnetic flux density in the gap is reduced, thereby canceling out the efficiency, and does not contribute much to the improvement in efficiency.

On the other hand, according to the conventional examples shown in FIGS. 16 and 17, since a dedicated magnetic circuit is used for focusing and tracking, the utilization efficiency of each drive coil is reduced as shown in FIG. 18 (D). A high-performance objective lens drive can be expected. However, since a dedicated magnetic circuit is used for focusing and tracking, the cost increases. Also, it is difficult to provide an opposing yoke on the lens holder side in the tracking magnetic circuit, and in fact, the magnetic flux density of the coil portion is low, and the efficiency is not necessarily high.

The present invention has been made to solve the problems of the prior art, and provides a low-cost and highly-reliable objective lens driving device which is small in size, has high efficiency, and is realized with a small number of components. The purpose is to:

(Means for Solving the Problems) According to the present invention, a lens holder on which an objective lens is mounted is slidably supported in an axial direction and a circumferential direction with respect to an axis, and is formed on a line connecting the objective lens optical axis and the axis. On the other hand, partial cylindrical magnets having the same curvature are arranged on both sides, and the partial cylindrical magnets on both sides are composed of a focusing magnet part and a tracking magnet part arranged adjacently in the circumferential direction, The focusing magnet section is paired at an opposing position across the axis, and the tracking magnet section is paired at an opposing position across the axis. The focusing magnet section has a magnetic pole in the axial direction. The tracking magnet section is formed with magnetic poles formed in a circumferential direction, and the focusing magnet section and the tracking magnet section are respectively opposed to each other. The drive coil for focusing and the drive coil for tracking are arranged on the surface of the lens holder having the same curvature,
The yokes are arranged inside and outside with the partial cylindrical magnets on both sides and the focusing drive coil and the tracking drive coil interposed therebetween, and the inner and outer yokes are common to the focus magnet section and the tracking magnet section. The focus drive coil is for moving the objective lens in the optical axis direction by a thrust generated between the focus drive coil and the focus drive coil, and the tracking drive coil is a tracking magnet. The objective lens is moved in a direction perpendicular to the optical axis of the objective lens by a thrust generated between the optical axis and the optical axis.

(Operation) The objective lens is moved in the optical axis direction by the thrust generated between the focusing magnet and the focusing drive coil, and the focusing operation is performed. The thrust generated between the tracking magnet and the tracking drive coil moves the objective lens in a direction perpendicular to the optical axis, thereby performing a tracking operation.

Embodiment An embodiment of the objective lens driving device according to the present invention will be described below with reference to FIGS. 1 to 10.

1 to 4, reference numeral 1 denotes a lens holder. The lens holder 1 is supported so as to be rotatable around a fixed shaft 7 and movable along the shaft 7. An objective lens 2 is attached to the lens holder 1 with its optical axis parallel to the axis 7. The lens holder 1 also has
A balancer 8 is fixed to the opposite side of the objective lens 2 about the axis 7. A pair of focusing drive coils 4 and tracking drive coils 3 are fixed to the outer peripheral surface of the lens holder 1 at symmetrical positions with respect to the shaft 7.
The outer peripheral surface of the lens holder 1 to which the focus driving coil 4 and the tracking driving coil 3 are fixed is a continuous partial cylindrical surface having the same curvature about the axis 7. It is bent along the partial cylindrical surface and fixed to the lens holder 1.

The shaft 7 is erected on the center boss of the yoke 9. The yoke 9 is formed in a fan shape on both sides with the shaft 7 interposed therebetween, and the outer peripheral edge of the fan shape is bent at a right angle and rises so as to face the coils 4 and 3. Each rising portion of the yoke 9 is formed along an arc centered on the shaft 7, and a partially cylindrical magnet 6 is fixed to the inner surface of the rising portion. The magnet 6 is integrally molded with, for example, a resin binder. Magnet 6
5 and 7, a groove 6c is formed in the middle portion in a direction parallel to the shaft 7, and the focusing magnet portion 6a and the tracking magnet portion 6b are formed with the groove 6c as a boundary. Is divided into The focusing magnet 6a is magnetized so that the north and south poles are aligned in the direction of the axis 7, while the tracking magnet 6b is magnetized in a direction perpendicular to the magnetizing direction of the focusing magnet 6a. Thus, the N pole and the S pole are formed in the circumferential direction. By thus integrally forming the magnet portions 6a and 6b, the magnet portions 6a and 6b are partially cylindrical magnets having the same inner diameter curvature and the same outer diameter curvature, respectively, and are perpendicular to the center axis of the curvature. It is magnetized by being divided in parallel and mutually perpendicular directions, and is arranged adjacent to a surface having the same continuous curvature.

As shown in FIG. 6, the focus driving coil
41 is formed to be a horizontally long rectangle, and is arranged such that its long side faces each magnetic pole of the focusing magnet section 6a. The tracking drive coil 3 is formed to have a vertically long rectangular shape, and is disposed such that a long side thereof faces each magnetic pole of the tracking magnet portion 6b.

The focusing magnet section 6a is located at a position opposite to the axis 7 and forms a pair.
Are also opposed to each other with the shaft 7 interposed therebetween.
Similarly, both the focus drive coil 4 and the tracking drive coil 3 make a pair, and these coil pairs are arranged on both sides with respect to a line connecting the optical axis of the objective lens 2 and the axis 7.

Another yoke 5 is fixed to the yoke 9 with the magnet portions 6a and 6b and the coils 3 and 4 interposed therebetween. Like the yoke 9, the yoke 5 is formed in a fan shape on both sides of the shaft 7, and the outer peripheral edge of the fan shape is bent at a right angle and rises. The rising portion is formed along an arc centered on the axis 7. The rising portion penetrates through the window hole 1a formed in the lens holder 1 with a sufficient space, and the magnet portions 6a,
6b. The yokes 5 and 9 include a focusing magnet 6a and a tracking magnet 6b, a focusing driving coil 4 and a tracking driving coil 3 respectively.
It is arranged inside and outside with. Then, the yoke 5 and the yoke 9 are integrated to form the focusing magnet 6a.
And a yoke common to the tracking magnet 6b.

Next, the operation of the above embodiment will be described by dividing focusing driving into tracking driving.

(1) Focusing drive FIG. 9 shows the relationship between the magnetic flux generated by the focusing magnet section 6a and the focusing drive coil 4. When a drive current flows through the coil 4, a thrust is generated by the drive current and the magnetic flux in the magnetic circuit. This thrust is equally generated in the focus driving coil 4 symmetrically arranged on the support shaft 7, and the objective lens 2 moves in the hole axis direction together with the lens holder 1 to perform a focusing operation. The center of gravity of the movable part including the objective lens 2 is aligned with the support shaft 7,
Therefore, the movable portion is driven in the optical axis direction, that is, in the focusing direction, without causing swinging or irregular vibration.

(2) Tracking drive FIG. 10 shows the relationship between the magnetic flux generated by the magnetization of the tracking magnet unit 6b and the tracking drive coil 3. When a drive current flows through the coil 3, a thrust is generated by the drive current and the magnetic flux in the magnetic circuit. This thrust becomes a rotational moment about the support shaft 7 in a direction perpendicular to the focus drive coil 4, that is, the objective lens 2 is driven together with the lens holder 1 in the tracking direction to perform a tracking operation.

In the illustrated embodiment, the pair of focus drive coils 4 and tracking drive coils 3 are each a flat plate-shaped coil having the same shape. This is a simpler and easier-to-wind structure than the air-core type coil seen in the conventional example, and is most suitable for high-occupancy-type high-performance coils such as printed coils and laminated coils, and low-cost coils. Shape. Since the magnets facing each coil having the same shape are provided in a direction in which the magnetization directions are orthogonal to each other,
Thrust generated in each coil is generated in a direction orthogonal to each other.

The shape and magnetization pattern of the coil can be optimized and distributed according to the driving sensitivity required for the objective lens driving device. FIG. 18 (E) shows the utilization efficiency of the focus drive coil and the tracking drive coil in the above embodiment, that is, the ratio of the length of the portion where the thrust effectively acts to the entire winding length of the coil. As apparent from FIG. 18 (E), according to the illustrated embodiment, the same use as the objective lens driving device having the dedicated focusing magnetic circuit and the tracking magnetic circuit as described with reference to FIG. 16 is performed. Efficiency can be achieved.

Further, since the focus driving coil and the tracking drive coil are arranged on a surface having the same curvature continuously without overlapping winding, the gap where each coil is located can be suppressed to be small. Magnetic flux density of 10
It can be increased to about 0 to 250%, and the driving force can be greatly improved.

Furthermore, the drive coil for focusing and the drive coil for tracking can have the same shape or a similar shape and can be used in common. By doing so, the production equipment can be shared and the cost can be reduced from this aspect. Can also.

As shown in the illustrated embodiment, the magnet can be used to combine the focus magnet unit and the tracking magnet unit into a single unit, thereby reducing the number of parts. In addition, since the magnet for focusing and the magnet for tracking can be formed on the integral magnet by polarization magnetization, the magnetization cost can be suppressed to a level that is not much different from the case of monopolar magnetization. The performance can be increased without increasing the performance.

However, depending on the design of the entire objective lens driving device, as shown in FIG. 8, the focusing magnet section 6a and the tracking magnet section 6b may be used separately.
Of course, also in this case, the focusing magnet 6a and the tracking magnet 6b each have a partial cylindrical shape having the same inner curvature and the same outer curvature, and are perpendicular and parallel to the center axis of the curvature. It is divided and magnetized in directions orthogonal to each other, and is arranged adjacent to a surface having the same continuous curvature.

(Effects of the Invention) According to the present invention, the following effects are obtained.

The drive coil for focusing and the drive coil for tracking are arranged on a continuous common surface without overlapping in the radial direction, so that the magnetic gap where each coil is located is small, and high-density magnetic flux is obtained. Objective lens driving device with a high level can be obtained.

The focus drive coil and the tracking drive coil are arranged on a continuous common surface, and similarly, the focus magnet and the tracking magnet are also arranged on a continuous surface having the same curvature. Can be easily made uniform, so that an objective lens driving device of uniform quality without variation in sensitivity can be obtained.

The focus drive coil and the tracking drive coil are arranged on a continuous common surface, and the focus magnet and the tracking magnet are similarly arranged on a continuous surface having the same curvature. It is easy to obtain the positional accuracy between the magnet and the tracking magnet and the positional accuracy between the focusing drive coil and the tracking drive coil, and this contributes to obtaining an effect.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of an objective lens driving apparatus according to the present invention, FIG. 2 is a longitudinal sectional view of the above embodiment, FIG. The figure is an enlarged plan view of the magnet and coil portions of the above embodiment, and FIG.
Fig. 6 is a front view of the magnet in the above embodiment, Fig. 6 is a front view of the coil in the above embodiment, Fig. 7 is a perspective view of the magnet, Fig. 8 is a perspective view showing a modification of the magnet, FIG. 9 is an explanatory diagram showing the state of the magnetic flux in the focusing magnetic circuit in the embodiment, FIG. 10 is an explanatory diagram showing the state of the magnetic flux in the tracking magnetic circuit in the embodiment,
FIG. 11 is a plan view showing an example of a conventional objective lens driving device,
FIG. 12 is a plan view showing another example of the conventional objective lens driving device, FIG. 13 is a plan view showing still another example of the conventional objective lens driving device, and FIG. FIG. 15 is a perspective view showing a yoke which similarly constitutes a magnetic circuit, FIG. 16 is a plan view showing still another example of a conventional objective lens driving device, and FIG. FIG. 18 is a comparative diagram showing a comparison between the utilization efficiency of each coil in each of the conventional examples and the embodiment of the present invention. 2 ... objective lens, 3 ... tracking drive coil,
4. Focusing drive coil, 6a Focusing magnet, 6b Tracking magnet

Claims (1)

(57) [Claims] 1. A lens holder on which an objective lens is mounted is slidably supported in an axial direction and a circumferential direction with respect to an axis, and has the same curvature on both sides with respect to a line connecting the objective lens optical axis and the axis. The partial cylindrical magnets having the magnets are disposed, and the partial cylindrical magnets on both sides include a focusing magnet portion and a tracking magnet portion which are disposed adjacent to each other in a circumferential direction, and the focusing magnet portion has the axis. A pair of the tracking magnet portions are formed in a pair at the opposed position with the axis interposed therebetween. The focusing magnet portion has a magnetic pole formed in the axial direction, and the tracking magnet portion is formed in the axial direction. The magnetic pole is formed in the circumferential direction, and the focusing drive is performed by opposing the focusing magnet and the tracking magnet. A coil and a tracking drive coil are arranged on the surface of the lens holder having the same curvature, and yokes are provided inside and outside of the partial cylindrical magnets on both sides of the lens holder and the focusing drive coil and the tracking drive coil. The inner and outer yokes are common and fixed integrally to the focusing magnet section and the tracking magnet section, and the focusing drive coil is driven by an objective lens by a thrust generated between the focusing magnet section and the focusing magnet section. In the direction of the optical axis, and the tracking drive coil moves the objective lens in a direction perpendicular to the optical axis by a thrust generated between the tracking drive coil and the tracking magnet unit. Objective lens driving device.