JPH0687315B2 - Optical head objective lens drive - Google Patents

Description

The present invention relates to an objective lens driving device provided in an optical head of an optical disc device.

<Prior Art> An optical disk device is a device that records information on an optical disk according to a command from a computer or the like, and reads and reproduces the recorded information. A drive device that rotates a disc-shaped optical disk, an optical head, And these control devices.

Generally, this type of optical disk device focuses a laser light beam of a semiconductor laser or the like on an optical disk with an objective lens,
Fine tracks on the optical disc (for example, a gap of about 1.6μ
m) is scanned to record information on the track or read information on the track. Therefore, the optical head of the optical disk device has a focus control for keeping the laser light beam in an appropriate converged state (for example, a spot diameter of 1 μm), a track control for keeping the converged spot out of the track, and an access control for searching a desired track. It has three functions.

FIG. 5 is a schematic configuration diagram for explaining this type of optical head.

As shown in the figure, this optical head is a light source such as a semiconductor laser.
An optical system including 51, a beam splitter 52, and an objective lens 53, a two-divided photodiode 54, the objective lens 53, a focus direction F which is a direction perpendicular to the optical disc surface LDa of the optical disc LD, and a radial direction of the optical disc LD. And a magnetic circuit device 55 for moving in the track crossing direction T along.

Then, the laser light beam 56 from the light source 51 is transmitted through the beam splitter 52, and then is passed through the objective lens 53 to the optical disc.
It is converged to a point P ₁ on the LD. The reflected light 56a from the optical disk LD passes through the objective lens 53 to have a large beam diameter, is then reflected by the beam splitter 52 and is deflected at a right angle, and is incident on the light receiving surface 57 of the two-divided photodiode 54.
The two-divided photodiode 54 has a light-receiving surface 57 divided into two light-receiving regions 57a and 57b.
The track error is detected based on the difference in the amount of light received by a and 57b. The magnetic circuit device 55 is driven by the track error signal.
Is controlled so that the objective lens 53 moves in the track crossing direction T
Is moved to, and track control is performed.

Further, the magnetic circuit device 55 is controlled by the focus error signal detected by the focus error detecting means (not shown), the objective lens 53 is moved in the focus direction F, and thereby the focus control is performed.

In such a track control system, when the scanning track position is moved from the point P ₁ to another point P ₂ , the reflected light 56b from the point P ₂ is the objective as shown by the broken line in FIG. Lens 5
Deviate from the optical axis of 3. In that case, the beam position incident on the light receiving surface 57 of the two-divided photodiode 54 shifts in proportion to the movement amount of the objective lens 53, and an offset occurs in the track error signal. Therefore, the moving range of the objective lens 53 in the track crossing direction T is limited to about 100 μm.

Therefore, access control in which the range of movement of the objective lens 53 in the track crossing direction T is significantly wider than in track control is
It is necessary to move the entire optical head by a motor or the like. Therefore, the mass of the optical head greatly affects the access speed.

Conventionally, in order to increase the access speed, a method has been proposed in which the objective lens 53, the magnetic circuit device 55, and the beam splitter 52 are movable and other optical systems are fixed. In this method, the mass of the movable part is considerably reduced as compared with the case where the entire optical head is moved, but the magnetic circuit device 55 formed of heavy parts such as a permanent magnet and a yoke is used as the movable part. Since it is included, the access time is several times that of the magnetic disk.

Therefore, in order to increase the access speed of the optical head, an objective lens driving device as shown in the perspective view of FIG. 6 has been devised (Japanese Patent Laid-Open No. 59-11544).

As shown in the figure, a magnetic circuit device 62 provided with two magnetic gaps 61 having a length covering the entire track is fixedly provided in the track crossing direction T for a long time. This magnetic circuit device 62 is
It is composed of a permanent magnet 63 and a yoke 64. Support plates 65 are provided above and below the magnetic circuit device 62 so as to be sandwiched therebetween so as to be connected to each other. An objective lens 66 and a movable coil 67 are fixed to the support plate 65.

The upper and lower support plates 65 are provided with rollers 68 provided at their four corners.
It is supported by the two frames 69 via the so as to be movable up and down, that is, movable in the focus direction F. These two frames 69 are connected to each other by a connecting frame 70,
A guide rail 72 attached to the magnetic circuit device 62 is supported via a roller 71 so as to be movable along the magnetic circuit device 62. That is, this objective lens driving device is
The support plate 65 with the fixed coil is provided with a focusing coil F and a track crossing direction T by an electromagnetic force generated by a focusing coil and a tracking coil (not shown) that form the movable coil 67.
The optical disc is configured so that it can move while covering the entire track.

Therefore, in the case of the objective lens driving device having the above configuration, since the magnetic circuit device 62 having a large mass is fixed, the mass of the movable part can be further reduced.

<Problems to be Solved by the Invention> However, in the objective lens driving device having the above configuration, the structure of the movable portion for moving the objective lens 66 in the focus direction F and the track crossing direction T is complicated, and the number of parts is large.
Moreover, there is a drawback that the rigidity of the movable part is low. If the rigidity is low, the structural resonance frequency of the movable part becomes low. Normally, the focus and track control system of the optical head is several kH.
A z servo band is required and the structural resonance frequency of the moving part must be at least five times higher than this servo band. Therefore, when the structural resonance frequency of the movable portion is low, the servo band is limited and the tracking characteristic is deteriorated.

In the configuration of the objective lens driving device, the end portion of the yoke 64 is
Since the magnetic flux concentrates on 64a and causes magnetic saturation, the magnetic flux density in the magnetic gap 61 cannot be increased so much, and thus sufficient thrust cannot be applied to the movable part.

To increase the magnetic flux density, the yoke 64 may be thickened, but this also widens the support plate 65, the frame 69, and the movable coil 67, resulting in an increase in mass. Moreover, as the support plate 65 and the frame 69 become wider, their rigidity further decreases,
As a result, the following characteristic is deteriorated.

Further, if an attempt is made to increase the rigidity of the support plate 65 and the frame 69, the mass of the movable portion is increased, and the access speed cannot be increased sufficiently, and the access time cannot be shortened significantly.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides a light beam emitted from a fixedly arranged optical device in a track crossing direction along a radial direction of the optical disk. By deflecting in a focus direction perpendicular to the surface and converging on the optical disk surface by the objective lens, and by receiving the reflected light of the light beam from the optical disk surface by the optical device, An objective lens driving device for an optical head, which is provided in an optical head of an optical disc device for recording and reproducing information, and which moves the objective lens in the focus direction and the cross-track direction to perform focus control, track control, and access control, A yoke, a permanent magnet and a plate-shaped magnetic circuit device are fixedly arranged. In the magnetic circuit device, a lens moving hole having a substantially oval shape and magnetic gaps which are located on both sides of the lens moving hole and in which the permanent magnets are provided are long in the track crossing direction and penetrate in the focusing direction. A beam introducing hole for guiding the light beam from the optical device to the lens moving hole is provided, a guide member whose guide direction is aligned with the track crossing direction is fixedly arranged, and a cylindrical beam deflecting portion is projected on the substrate. A beam deflector for deflecting the light beam that has passed through the beam introduction hole of the magnetic circuit device in the focus direction is attached to the beam deflecting part, and the beam deflecting part is provided in the magnetic circuit device. The substrate is slidably inserted into the lens moving hole so as to be movable in the track crossing direction, and the substrate is slidably attached to the guide member. A lens boulder is formed by forming a tubular portion connected to the upper and lower plates in a state of being opened in the center of the upper and lower plates, in a frame body that is formed of a bottom plate, a lower plate, and two side plates, and that is open in the track transverse direction. The objective lens is attached to the upper opening of the cylindrical portion, and the upper and lower plates are formed with overhanging portions projecting in the track crossing direction, and the lens holder is attached to the projecting portion in the focus direction and the track. A focusing coil and a tracking coil that move in the transverse direction are assembled, and the side plate and both coils are loosely inserted into the magnetic gap of the magnetic circuit device, and the beam deflection portion of the carriage is attached to the cylindrical portion. Sliding slidably allows the lens holder to move in the focus direction on the carriage. The beam deflector of the carriage and the cylindrical portion of the lens holder are provided with holes, and the light beam guided to the lens moving hole of the magnetic circuit device is guided to the beam deflector of the carriage. The light beam from the beam deflector is converged on the optical disk surface by the objective lens of the lens boulder.

<Operation> With the above configuration, the objective lens moves in the focus direction and the track crossing direction by passing a current through the focusing coil and the tracking coil.

Further, the end of the portion of the yoke constituting the magnetic circuit device that faces the permanent magnet, that is, the portion that surrounds the lens moving hole can be formed thick, so that the magnetic flux is not concentrated at the end.

<Example> An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially cutaway perspective view showing an objective lens driving device for an optical head according to the present invention, and FIG. 2 is a side sectional view of the same portion omitted.

As shown in the figure, the objective lens driving device 1 is an optical disc.
A light beam L ₁ emitted from a fixedly arranged optical device 2 facing the optical disc surface LDa of the LD in a track crossing direction T along the radial direction of the optical disc LD is perpendicular to the optical disc surface LDa. A light that is deflected in a different focus direction F and converges on the optical disk surface LDa, guides the reflected light L ₂ of the light beam L ₁ from the optical disk surface LDa to the optical device 2, and converges on the optical disk surface LDa. The beam L ₁ is translated in the track crossing direction T. The objective lens driving device 1 includes a magnetic circuit device 3 that is fixedly arranged, a guide member 4 that is formed by fixing two rods, and slides on the guide member 4 below the magnetic circuit device 3. Carriage 5 that can be installed
And a lens holder 6 attached to the carriage 5 so as to be vertically movable.

The magnetic circuit device 3 is formed in a plate shape by combining a main yoke 7 and a sub-yoke 8 as shown in the plan sectional views of FIGS. 1 and 3, and is an ellipse located at the center. A lens moving hole 9 having a shape and two substantially rectangular magnetic gaps 10 located in parallel to each other on both sides of the lens moving hole 9 are provided so as to be long in a track crossing direction T and penetrate in a focus direction F. There is. Further each magnetic gap 10
A plate-shaped permanent magnet 11 is provided in the state of being fixed to the main yoke 7 located outside the magnetic gap 10. Also, the surface 3a of the magnetic circuit device 3 facing the optical device 2
As shown in FIGS. 1 and 2, there is provided a beam introducing hole 12 for guiding the light beam L ₁ from the optical device 2 to the lens moving hole 9.

By configuring the magnetic circuit device 3 as described above, the ends 7a and 8a of the portions of the two yokes 7 and 8 facing the permanent magnet 11, that is, the portions surrounding the lens moving hole 9 can be formed thick. That is, the concentration of the magnetic flux B formed as shown by the dotted line in FIG. 3 at the ends 7a, 8a is alleviated without increasing the thickness of the portions of the two yokes 7, 8 surrounding the lens moving hole 9,
Therefore, the magnetic flux density in the magnetic gap 10 can be increased.

The guide member 4 is fixedly arranged so that the guide direction, that is, the longitudinal direction thereof is aligned with the track crossing direction T.

As shown in the exploded views of FIG. 2, FIG. 3 and FIG. 4, the carriage 5 is formed by projecting a cylindrical beam deflecting portion 14, for example, a cylindrical beam deflecting portion 14 on the upper surface of the substrate 13. In a state in which 14 is loosely inserted in the lens moving hole 9 of the magnetic circuit device 3, it is supported by the guide member 4 via a slide bearing 15 provided on the substrate 13. Furthermore, inside the beam deflection unit 14,
As a beam deflector, a plane mirror 16 is fixed in a state of being tilted at 45 degrees, and a hole 17 for passing the light beam L ₁ is formed in the peripheral wall of the beam deflector 14.

The carriage 5 having the above-described structure can be easily manufactured by adhering and fixing the beam deflecting portion 14 formed by processing a cylinder of aluminum alloy or the like to the substrate 13 formed of, for example, plastic or ceramic material.

The lens holder 6 is, as shown in FIG. 2 and FIG.
A frame body formed by an upper plate 18, a lower plate 19 and two side plates 20 and opened in the cross-track direction.
A tubular portion 22 is formed on the upper and lower plates 18 and 19 and is connected to the upper and lower plates 18 and 19 in a state of being opened at the centers thereof. The cylindrical portion 22 is formed in a cylindrical shape in the present embodiment so that the beam deflecting portion 14 of the carriage 5 can be loosely inserted, and the upper opening portion 23 thereof has an objective lens.
24 is attached with its optical axis aligned with the focus direction F. In addition, a hole 25 for passing the light beam L ₁ is formed in the peripheral wall of the cylindrical portion 22.
Has been drilled. Further, the upper plate 18 and the lower plate 19 have overhanging portions 18a extending in the track transverse direction T,
19a is formed. And the upper and lower overhangs 18a, 1
The two tracking coils 26 are wound around 9a, and the focusing coil 27 wound so as to surround the objective lens 24 is provided on the overhanging portion 18a of the upper plate 18.
It is superposed on the upper tracking coil 26, and both ends thereof are bent and fixed to the side plate 20 while being adhered thereto. As a result, the lens holder 6
When attached to the carriage 5, the magnetic flux of the magnetic circuit device 3 penetrates into both coils 26 and 27. If a current is applied to both coils 26, 27 in such a state, thrust in the focus direction F and the track crossing direction T due to electromagnetic force is generated.

As shown in FIGS. 1 and 3, the lens holder 6 has the side plate 20 and the coils 26 and 27 loosely inserted into the magnetic gap 10 of the magnetic circuit device 3 and is inserted into the cylindrical portion 22. By loosely inserting the beam deflection unit 14 of the carriage 5, the carriage 5 is attached so as to be movable in the focus direction F. That is, the cylindrical portion 22 of the lens holder 6 is loosely inserted in the lens moving hole 9 of the magnetic circuit device 3 and can move in the track crossing direction T depending on the shape of the lens moving hole 9. Moreover, as shown in FIG. 4, the notch 28 provided at the lower end of the lens holder 6 and the substrate of the carriage 5
The rotation of the lens holder 6 is suppressed by engaging with the pin 29 protruding from the top of the lens holder 13.

The lens holder 6 having the above structure can be integrally formed of a plastic material having good sliding characteristics.

In the lens holder 6, the overhanging portions 18a of the upper plate 18 and the lower plate 19 around which the tracking coil 26 is wound,
The wall thickness of 19a is reduced to reduce weight. By constructing the lens holder 6 as described above and assembling the coils 26 and 27, the rigidity of the lens holder 6 is increased and the thickness of the portion loosely inserted into the magnetic gap 10 as shown in FIG. It can have a thickness of only 26,27. Therefore, the width w of the magnetic gap 10 can be narrowed to about 1 to 1.5 mm, and the thickness of the permanent magnet 11 can be reduced, whereby the magnetic circuit device 3 can be reduced in size and weight and the efficiency of the magnetic circuit can be improved. Can be increased.

Next, the operation of the objective lens driving device 1 having the above configuration will be described.

As shown in FIG. 2, from the optical device 2, the track crossing direction T
The light beam L ₁ emitted to the beam guide hole 12 of the magnetic circuit member 3, the hole 25 of the lens holder 6 and the hole 17 of the carriage 5 are emitted.
Is reflected by the plane mirror 16 in the beam deflector 14, is deflected by 90 degrees in the focus direction F, and enters the objective lens 24 along its optical axis. By this objective lens 24, the light beam L ₁ is focused on the optical disc surface LDa. In this way, the reflected light L ₂ of the light beam L ₁ irradiated on the optical disk surface LDa is
The light beam L ₁ travels backward in the same optical path and returns to the optical device 2. Then, based on the reflected light L ₂ , each detection is performed by the focus / track error detector and the signal detector in the optical device 2.

At the time of focus control, a current based on the focus error signal detected as described above is caused to flow through the focusing coil 27, and the electromagnetic force causes the lens holder 6 to move in the up-down direction, that is, the focus direction F, so that the objective lens 24 moves on the surface of the optical disk LD. To follow.

At the time of track control, a current based on the track error signal obtained by the above detection is passed through the tracking coil 26, and the electromagnetic force thereof moves the lens holder 6 in the lateral direction, that is, in the track crossing direction T, and the objective lens 24 moves the optical disk surface LDa.
Follow the blur of the track. At that time, the lens holder 6
In order to move with the carriage 5, that is, the objective lens
Since the 24 and the plane mirror 16 move as a unit, the light beam
L ₁ and its reflected light L ₂ never deviate from the optical axis.

At the time of access control, a current corresponding to the difference between the designated track and the current track is made to flow through the tracking coil 26 by a control circuit (not shown), and the lens holder 6 moves in the track crossing direction T as in the case of the above track control. To be done. Therefore, the respective dimensions of the magnetic circuit device 3 and the lens holder 6 are set so that they can be accessed over the entire track of the optical disc LD. Also, during this access control, the light beam L ₁ and its reflected light L ₂ will not deviate from the optical axis, as in the above-mentioned track control.

Further, the mass of the movable part including the carriage 5 and the lens holder 6 is reduced to 5 to 10 g including the coils 26 and 27,
Moreover, since the magnetic flux density in the magnetic gap 10 is sufficiently increased as described above, ultra-high speed access equivalent to that of an ultra-high speed magnetic disk is possible.

The focus control and the track control are simultaneously performed in a combined manner as needed, but when the access control is performed, the track control is once turned off and the objective lens
After 24 has moved to the desired position, it is turned on again.

<Effects of the Invention> As described above in detail, in the objective lens driving device of the present invention, the structure of the movable part is simple, and the movable part can be made lightweight and highly rigid. Further, the magnetic flux density in the magnetic gap can be increased. Therefore, high follow-up characteristics can be obtained, and ultra-high-speed access equivalent to that of an ultra-high-speed magnetic disk can be achieved.

Further, the objective lens driving device of the present invention can operate stably over the entire track of the optical disc because the light beam and the reflected light from the optical disc surface do not deviate from the optical axis in both track control and access control. .

[Brief description of drawings]

FIG. 1 is a partially broken perspective view showing an objective lens driving device of the present invention, FIG. 2 is a partially omitted side sectional view showing the objective lens driving device of the present invention, and FIG. 3 is a magnetic circuit device. FIG. 4 is an exploded view of a carriage and a lens holder, FIG. 5 is a schematic configuration diagram illustrating an optical head, and FIG. 6 is a perspective view illustrating a conventional example. 1 ... Objective lens driving device, 2 ... Optical device, 3 ... Magnetic circuit device, 4 ... Guide member, 5 ... Carriage, 6 ... Lens holder, 7 ... Main yoke, 8 ... Sub-yoke, 9 ...... Lens moving hole, 10 ...... Magnetic gap, 11 ...... Permanent magnet, 12 ...... Beam introduction hole, 13 ...... Substrate, 14 ...... Beam deflection part, 16 ...... Plane mirror, 17 ...... hole, 18 ...... Upper plate, 18a …… Overhang part, 19 …… Lower plate, 19a …… Overhang part, 20 …… Side plate, 21 …… Frame, 22 …… Cylinder part, 24 …… Objective lens, 25 …… Hole, 26 …… Tracking coil, 27 …… Focusing coil, L ₁ …… Light beam, L ₂ …… Reflected light, LD …… Optical disk, LDa …… Optical disk surface.

Claims (1)

[Claims] 1. A light beam emitted from a fixedly arranged optical device in a track crossing direction along a radial direction of an optical disc is deflected in a focus direction perpendicular to an optical disc surface of the optical disc, and the objective lens is used to The optical head is provided in an optical head of an optical disc device that records and reproduces information on the optical disc by converging on the optical disc surface and receiving the reflected light of the light beam from the optical disc surface by the optical device. In an objective lens driving device of an optical head that moves the objective lens in the focus direction and the track crossing direction to perform control, track control, and access control, a magnetic circuit device formed in a plate shape is fixed by a yoke and a permanent magnet. And a lens moving hole of a substantially elliptical shape and the lens in the magnetic circuit device. A beam that guides the light beam from the optical device to the lens moving hole while providing a magnetic gap that is located on both sides of the moving hole and that has the permanent magnet therein and that is long in the track crossing direction and penetrates in the focus direction. An introduction hole is provided, a guide member whose guide direction is aligned with the track crossing direction is fixedly arranged, and a cylindrical beam deflecting portion is projectingly provided on a substrate to form a carriage, and the beam deflecting portion includes the magnetic circuit device. A beam deflector for deflecting the light beam that has passed through the beam introduction hole in the focusing direction is installed, and the beam deflecting unit is loosely inserted inside the lens moving hole of the magnetic circuit device so as to be movable in the track crossing direction. , The substrate is slidably attached to the guide member, and the substrate is composed of an upper plate, a lower plate and two side plates. In the frame body opened in the transverse direction of the rack, a lens portion is formed by forming a cylindrical portion connected to the upper and lower plates in a state of being opened at the center of the upper and lower plates to form a lens holder, and the upper opening portion of the cylindrical portion is formed. A focusing coil and a tracking coil are attached to which an objective lens is attached, and projecting portions projecting in the track crossing direction are formed on the upper and lower plates, and the lens holder is moved to the projecting section in the focus direction and the track crossing direction, respectively. And the side plate and both coils are loosely inserted into the magnetic gap of the magnetic circuit device, and the beam deflecting portion of the carriage is slidably loosely inserted into the cylindrical portion so that the lens holder Is attached to the carriage so as to be movable in the focus direction, and the beam deflection section of the carriage and the lens holder are attached. Holes are provided in the respective cylinders, the light beam guided to the lens moving hole of the magnetic circuit device is guided to the beam deflector of the carriage, and the light beam from the beam deflector is guided by the objective lens of the lens holder. An objective lens driving device for an optical head, which is converged on the optical disk surface.