JPH04178927A - Objective lens drive device - Google Patents

Abstract

PURPOSE:To obtain a small device with an improved controllability by allowing the optical axis of an objective lens to be passed within a magnetic gap and then driving the objective lens in two directions of focus and tracking using a magnetic flux of a magnetic gap. CONSTITUTION:Since magnetic poles N and S of a permanent magnet 24 directly face each other, there is no opposing yoke and a magnetic field between the magnetic poles N and S and an electromagnetic force which exerted on a coil which is provided at an objective lens retaining member 28 which is positioned within the inside allow the objective lens 32 to be driven in focus direction. Namely, since a coil 33 is located between coils 27a and 27b, the same magnetic flux passes through four coils 27a, 27b, and 33, a permanent magnet 24 can be reduced for a movable range of a carriage 25, and a yoke 22 can also be reduced, thus enabling rigidity of the objective lens retaining member 28 to be increased, frequency characteristics in focus direction to be improved, controllability to be improved, and also miniaturization and light weight to be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an objective lens driving device for driving an objective lens for an optical disc in a focusing direction and a tracking direction in an optical disc device.

[Prior Art] -119 In an optical disk device, two types of coils are used to move an objective lens in two directions, a focusing direction and a tracking direction, in order to record, erase, and reproduce information on an optical disk. It has a magnetic circuit, and another type of coil and magnetic circuit, ie, a linear motor, for seeking the objective lens to any position in the radial direction on the disk.

In recent years, for the purpose of shortening access time, etc., the actuator for tracking direction drive and linear motor have been made common, and the magnetic circuit for focus direction drive has also been shared with that of the linear motor, reducing the total weight and simplifying the drive unit. Objective lens driving devices have been proposed.

Figures 9 to 11 show a conventional example of an objective lens drive device in which the magnetic circuit is common to the drive section in the focus direction and the linear motor, with Figure 9 being a plan view and Figure 10 being a sectional view taken along line A-A. , FIG. 11 is a sectional view taken along line B-B. Two rails 1, 1 are arranged horizontally and in parallel on a base (not shown), between which, from the outside, permanent magnets 2.2 and 3.3 attached to the inner surface of the outer yoke 2. An inner yoke 4.4 is fixed parallel and symmetrically on the inside. The outer yoke 2 and the inner yoke 4 have the same length, and are connected at both ends by a relay yoke 5, respectively. Further, the length of the permanent magnet 3 is shorter than the interval between the relay yokes 5.5, and the length of the permanent magnet 3 is shorter than the interval between the relay yokes 5.5.
It is far from any of 5. A carriage 6 is located between the rails 1 and
1, and is movable in a direction parallel to the rails 1, that is, in the tracking direction. A coil 8.8 is fixed to the carriage 6, through which the outer yoke 2 and the permanent magnet 3 are respectively inserted. At the center of the carriage 6, vertically parallel leaf springs 9.9 are attached toward the front, and support the lens holding member 10 in front of the carriage 6 so as to be movable up and down. The lens holding member 10 is annular and has an inner yoke 4.4 passed through it, holds an objective lens 11 at the center of its upper surface with its optical axis vertical, and has a coil 12. 12 are provided. Further, a part of the carriage 6 extends to the center of the lens holding member IO, and holds the mirror 3 facing diagonally forward at an upward angle of 45 degrees directly below the objective lens 11.

With this configuration, when a current is passed through the coil 8, an electromagnetic force acts between the magnetic field between the permanent magnet 3 and the inner yoke 4 and the coil 8, so the carriage 6 is moved in the tracking direction by the current passed through the coil 8.8. It is driven by. Further, since the coils I2 and I2 receive force in the vertical direction due to the same magnetic field by passing current, the objective lens 11 can be driven in the focus direction.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional example, since the inner yokes 4, 4 are inserted into the lens holding member 10, the rigidity of the lens holding member 10 is reduced, resulting in a decrease in controllability. It is easy to cause secondary resonance. In addition, the lens holding member 10 becomes large,
This has a disadvantage in that it leads to an increase in the size of the carriage 6.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a compact objective lens drive device with good controllability.

[Means for Solving the Problems] In order to achieve the above-mentioned object, in the objective lens drive device according to the present invention, a driving unit that uses a common driving unit in the focus direction of the objective lens for the optical disk and a magnetic circuit of the linear motor is provided. In the system, an objective lens holding member is disposed within a magnetic gap of a single independent magnetic circuit having two magnets with magnetic poles of different polarities facing each other, and an optical axis of the objective lens is passed through the magnetic gap, The objective lens is driven in two directions, focusing and tracking, using the magnetic flux of the magnetic gap.

[Function] In the objective lens drive device having the above configuration, since the magnetic poles of the permanent magnets directly face each other, there is no opposing yoke, and the magnetic field between the magnetic poles and the coil provided in the objective lens holding member located therein are The objective lens is driven in the focus direction by the electromagnetic force acting between the two.

[Example] The present invention will be described in detail based on the example illustrated in FIGS. 1 to 8.

FIG. 1 is a perspective view of the first embodiment, and FIG. 2 is an exploded perspective view, in which two rails 21 and 21 are fixed to a substrate (not shown) on a horizontal plane in parallel to the tracking direction, and A yoke 22.22 is fixed in parallel to the yoke 22.
22 is a relay yoke 2 attached to the front and rear ends of its lower surface.
3.23, and plate-shaped permanent magnets 24.24 are attached to opposing surfaces of the yoke 22.22 with different magnetic poles facing each other. Rail 21.21, yoke 22.22, relay yoke 23.23 and permanent magnet 24
．． 24 is symmetrical except for the direction of the magnetic poles.

A carriage 25 is located between the rails 21 and 21, and an annular bearing member 26a is fitted into the bearing portion 25a on the left side of the carriage 25, through which the left rail 21 is inserted. Bearing members 26b and 26c are fitted into the two bearing parts 25b and 25c, and the right rail 2I is inserted through these, and the carriage 25 is movably supported in the front-rear direction by the rail 21.21. Arms 25d and 25e are provided inside the bearing portion 25a,
Arms 25f and 25g are provided inside the bearings 25b and 25c. Coil 2 between arms 25d and 25e
7a is sandwiched between the arms 25f and 25g, and the coil 2
7b is sandwiched between the coils 27a and 27b, and the yoke 22 and the permanent magnet 24 are inserted through both the coils 27a and 27b. A hollow, substantially rectangular lens holding member 28 is located at the center of the carriage 25, and this lens holding member 28 is connected to the arm 25d.
It is supported by a wire 30 made of an elastic member stretched between protrusions 29 provided on the upper part of each of ~25 g. Inside the lens holding member 28, a mirror 31 is fixed diagonally upward and forward, an objective lens 32 is fixed above it, and coils 33, 33 are bonded to the left and right outer surfaces.

A beam of light that enters parallel to the tracking direction from the front of the mirror 31 is reflected upward by the mirror 31, and then passes through the objective lens 32.
The beam is focused on an optical disc (not shown) via the . The lens holding member 28 is located in the magnetic field between the magnetic poles of the permanent magnets 24, 24, and when current is applied to the coils 33, 33, an electromagnetic force acts, and the coil moves to a position that balances the tension of the wire 30. 33.The objective lens 32 is
drive in the focus direction. Also, since the same magnetic flux crosses the coils 27a and 27b, the coil 2
By passing current through 7a and 27b, the carriage 25 is driven in the tracking direction, and the objective lens 32 is driven in the tracking direction.

With such a configuration, since the coils 33 and 33 are located between the coils 27a and 27b, the four coils 27a,
The same magnetic flux will pass through 27b and 33.33,
Permanent magnet 24.24 for the movable range of carriage 25
The length can be shortened.

The yoke 22.22 also has the advantage of being short.

Fig. 3 shows the dimensions of each part of the first embodiment, and Fig. 4 shows an example of the dimensions of the second embodiment. Coil 27a, 2
Divide 7b further into front and back.

Four coils 41a, 41b with a width of d2=di/2
, 41c, 41d, and the front and rear divided coils 41a
A coil 33 is arranged between 41b, 41c and 41d.

In such a configuration, the magnetic gap g2 becomes smaller by the sum of the thicknesses of the coils 27a and 27b plus the clearance between the coil 27a and the coil 33 and the clearance between the coil 27b and the coil 33. In other words, permanent magnet 2
The interval of 4.24, which was gl, will be narrowed to g2. This increases the permeance coefficient of the permanent magnet 24, so assuming that the required magnetic flux densities are equal, the permanent magnet 24 with a thickness of ■2 is thinner than the permanent magnet 24 with a thickness of ■1.
The yoke 22, which had a thickness of tl, becomes a yoke 43 with a thickness of tl, which is slightly thicker. Also, the length Wl of the permanent magnet 42 is longer than the length Wl of the permanent magnet 24 by the sum of d2×2 plus the clearance between the coils 41 and 33. It becomes possible to use a thin permanent magnet 42.

In the third embodiment, as shown in 5rg, the coils 51a and 5
1b, which are arranged in the tracking direction, and the width d3 of the coils 51a and 51b is the same as that of the coil 27 in the first embodiment.
a, equal to the width di of 27b, and the length w3 of the permanent magnet 42
and the thickness -3 and the thickness t3 of the yoke 43 are equal to w2, 2 and tl of the second embodiment. In this configuration, in addition to the advantages of the second embodiment, the convergence d3 of the coils 51a and 51b is is twice the width d2 of the coil 41, so the rigidity is high and the frequency characteristics of driving in the tracking direction are improved.

FIG. 6 shows a perspective view of the magnetic circuit of the first embodiment;
The figure shows the magnetic circuit of the fourth embodiment, in which an integral U-shaped yoke is used instead of the rear relay yoke 23 attached to the lower surface of the end of the yoke 22, 22 in the first embodiment. 61, and a relay yoke 23 is attached to the tip of the lower surface of the open portion of the yoke 61, so that the relay yoke 23 does not block the light flux that enters the mirror 31 on the carriage 25 from the front. In this fourth embodiment, the symmetry between the front and rear of the magnetic circuit is broken, but the number of parts is reduced.

FIG. 8 shows a fifth embodiment, in which the relay yokes 23, 23 in the first embodiment are omitted. Such a configuration prevents the magnetic field near the ends of the permanent magnets 24, 24 from passing through the relay yoke 23 and causing a short circuit.

In both of the above embodiments, the inner yoke 4.4 in the conventional example is eliminated, and the lens holding member 28 is disposed between the permanent magnets 24.24. The through hole provided in the member 10 is omitted.

[Effects of the Invention] As explained above, since the objective lens driving device according to the present invention does not have an inner yoke that passes through the objective lens holding member,
The objective lens holding member has high rigidity, improves frequency characteristics in the focus direction, and provides good controllability.
It is lightweight, operates at high speed, and can be made smaller.

[Brief explanation of the drawing]

1 to 8 show embodiments of the objective lens driving device according to the present invention, FIG. 1 is a perspective view of the first embodiment, and FIG.
The figure is an exploded perspective view, and FIGS. 3, 4, and 5 are magnetic circuits of the first embodiment, the second embodiment, and the third embodiment, respectively.
Lens holding member, top view of coil arrangement, Figures 6 and 7
8 are perspective views of the magnetic circuits of the first embodiment, the fourth embodiment, and the fifth embodiment, respectively, FIG. 9 is a plan view of the conventional example, and FIG. A sectional view, Figure 11 is B
-B sectional view. 21 is a rail, 22, 43, 61 is a yaw, 23 is a relay yoke, 24, 42 is a permanent magnet, 25 is a carriage, 26 is a bearing member, and 27a. 27b, 33.41a to 41d, 51a, and 51b are coils, 28 is a lens holding member, 29 is a projection, 30 is a wire, 31 is a mirror, and 32 is an objective lens. Patent applicant: Canon Co., Ltd. Figure 1 Figure 2 Figure 6 CI) -°-“] ■-1-1”

Claims (1)

[Scope of Claims] 1. In a drive system in which the drive unit for the focus direction of the objective lens for the optical disk and the magnetic circuit of the linear motor are common, a single independent magnet having two magnets with magnetic poles of different polarities facing each other. An objective lens holding member is disposed within the magnetic gap of the magnetic circuit, the optical axis of the objective lens is passed through the magnetic gap, and the objective lens is driven in two directions, focusing and tracking, using the magnetic flux of the magnetic gap. An objective lens driving device characterized by: 2. The objective lens driving device according to claim 1, wherein the tracking coil and the focus coil of the magnetic circuit are arranged so as to simultaneously cross the same magnetic flux.