JP2614455B2 - Objective lens actuator for optical head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens actuator of an optical head that enables efficient and highly accurate tracking control.

FIG. 3 is an exploded perspective view of an example of a conventional objective lens actuator. 1 is an objective lens, 2 is an objective lens 1
The objective lens holder 2 is provided with four parallel metal rods 4 attached to a support base 3 in a focusing direction (arrow (a) direction: Z direction) and a tracking direction (arrow (b)). Direction): supported so as to be displaceable in the Y direction).
A focusing coil 5 is provided so as to surround the outer periphery, and tracking coils 6 are attached to both sides in the longitudinal direction (X direction) of the metal bar 4. On the other hand, on the actuator base 7 side fixed to an optical head base (not shown),
A permanent magnet 8 for applying a magnetic field to each of the coils 5 and 6 is provided. The permanent magnet 8 is attached to a yoke 9 fixed to the actuator base 7, and an opposing yoke 10 is arranged opposite to the yoke 9. Reference numeral 11 denotes a circuit board provided on the support base 3, and energizes the coils 5, 5, 6, and 6 from the circuit board 11 through the metal rods 4 also serving as conductive wires.

In the objective lens actuator described above, the objective lens holder 2 and the objective lens 1 integrated therewith are driven in the focusing direction by the electromagnetic force between the permanent magnet 8 and the focusing coil 5, and the electromagnetic force between the permanent magnet 8 and the tracking coil 6. Is driven in the tracking direction.

[Problems to be Solved by the Invention] In the optical disk device, when the optical head accesses an arbitrary track of the optical disk, the tracking servo of the objective lens actuator is temporarily turned off and the optical head is fed. Since the optical head is moved at a high speed, the conventional objective lens actuator is difficult to accurately access a target track because the objective lens holder is swung by inertia force, and it takes time to access. was there. In addition, not only at the time of track access but also at the time of normal reproduction in which the tracking servo is operated, in the conventional configuration, when the objective lens follows the pits or the like of the optical disc, it deviates from the neutral position, so a servo system such as a fish pull system is used. In some cases, there is a problem that a tracking offset occurs.

Japanese Patent Application Laid-Open No. Sho 59-221840, "Objective lens driving device for optical disc player" includes an objective lens holder having an objective lens mounted thereon, which is supported by a plurality of parallel support rods so as to be displaceable in a focusing direction and a tracking direction. A lens actuator is disclosed. However, this is characterized in that a pair of focusing coils and a pair of tracking coils are assembled to an objective lens holder, and these four coils are driven in a common magnetic circuit composed of two permanent magnets. By using a common magnetic circuit for focusing drive and tracking drive, the entire device can be made compact.However, the magnetic circuit itself uses a common magnetic path that generates different magnetic forces depending on the position of the objective lens. Therefore, mutual interference is likely to occur, and there is a problem in control accuracy when the focusing control and the tracking control are required at the same time. In addition, 4 which also serves as a conducting wire to the coil
The two support rods are used to energize a pair of focusing coils, and the remaining two are used to energize a pair of tracking coils, so that the optical head can access any tracking of the optical disk. However, it is not possible to control the posture of the integrated tracking coil by passing currents in opposite directions to each other, for example, forcibly holding the objective lens at the neutral position. There is a problem that the holder is swung by the inertial force and it takes time to access.

Japanese Patent Laid-Open No. 55-146635 "Objective lens driving device" has permanent magnets attached to both sides of the objective lens in the tracking direction, and performs tracking control by an attractive force with an electromagnet provided opposite to the permanent magnet. An arrangement is disclosed. However, in this device, the objective lens holder is cantilevered by a pair of leaf springs whose base ends face each other across the objective lens, and a pair of movable members provided on the objective lens holder is provided with an oil damper such as silicone oil. This is a configuration that is viscously coupled to a pair of plate-shaped members via the same. That is, the objective lens holder itself prevents the vertical displacement by the movable member and the plate-shaped member that are viscously coupled. Therefore, regarding the focusing control, the tracking drive solenoid, the movable member or the plate-shaped member, and the fixed member supporting the same. However, there is a problem that it is difficult to perform efficient focusing control because the inertia weight of the movable part is enlarged because of the increase in the inertial weight of the movable part. A signal corresponding to a tracking error is applied to a pair of tracking drive solenoids facing a pair of permanent magnets fixed to both sides of the objective lens holder via an inverting amplifier. In this case, since neither of the pair of tracking drive solenoids is energized, it is difficult to forcibly hold the objective lens at the neutral position. Therefore, when the optical head accesses an arbitrary track of the optical disk. In addition, as the optical head is moved at a higher speed, the objective lens holder is shaken by the inertial force, so that it takes a longer time to access. Further, the pair of tracking drive solenoids composed of electromagnets and the pair of permanent magnets are arranged in a straight line, but the lines of magnetic force generated by the pair of permanent magnets pass through the cores of the pair of tracking drive solenoids. Since there is no yoke or magnetic path member to be controlled, the drive efficiency of the tracking drive solenoid is poor, and there is a problem that a drive current more than necessary must be supplied. In addition, the tracking position of the objective lens is not measured by the induced electromotive force generated in the tracking drive solenoid, and a tracking error signal generated by an optical sensor that guides the reflected light of the optical disk through the objective lens is not provided. Tracking control can only be performed by the

The present invention has been made in view of the above-mentioned conventional problems, and enables detection of a position of an objective lens in a tracking direction by a novel tracking driving means, whereby an objective lens holder is moved by an inertia force or the like at the time of track access. It is an object of the present invention to provide an objective lens actuator that can easily realize the suppression of the swing and the like.

[Means for Solving the Problems] In order to achieve the above object, an objective lens actuator for an optical head according to the present invention includes an objective lens holder for holding an objective lens, and an objective lens holder for moving the objective lens holder in a focusing direction and a tracking direction. It consists of a support base that supports cantilever so that it can be displaced, and a magnetic body that supports the support base,
An actuator base on which a pair of tracking drive yokes facing the tracking direction and a pair of focusing drive yokes facing a direction substantially orthogonal to the tracking direction are provided, and the tracking direction of the objective lens holder is A pair of focusing coils provided at both ends in a direction substantially orthogonal to each other, a pair of focusing drive permanent magnets disposed on the focusing drive yoke opposed to the pair of focusing coils, and A pair of tracking drive permanent magnets provided at both ends in the tracking direction, a pair of tracking drive solenoids disposed on the tracking drive yoke opposed to the pair of tracking drive permanent magnets, and the pair of tracking drive Solenoid Each is provided, the induced electromotive force generated in the respective tracking drive solenoid is measured at the time of tracking control, it is characterized by comprising a voltmeter for detecting the tracking position of the objective lens.

[Operation] In the above configuration, the current flowing through the solenoid is controlled to control the attraction or repulsion by the magnetic force between the permanent magnet provided on both sides of the objective lens holder and the solenoid, thereby driving the objective lens holder in the tracking direction. And the tracking drive of the objective lens can be performed. Further, the tracking position of the objective lens can be detected from the induced electromotive force generated in the tracking drive solenoid.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an exploded perspective view showing an embodiment of an objective lens actuator for an optical head according to the present invention, and FIG. 2 is a front view of the objective lens actuator shown in FIG. In each figure, the same components as those in FIG. 3 are denoted by the same reference numerals, and the description will be simplified.

1 and 2, reference numeral 1 denotes an objective lens and reference numeral 2 denotes an objective lens holder to which the objective lens 1 is attached. The objective lens holder 2 is composed of four parallel metal rods 4 made of, for example, phosphor bronze attached to a support table 3 in a focusing direction (arrow (a)).
Direction: Z direction) and tracking direction (arrow (b) direction: Y
Direction). A rectangular cylindrical focusing coil 20 is mounted on each side of the objective lens holder 2 in the longitudinal direction (X direction) of the metal frame, and tracking drive permanent magnets 21 are mounted on both sides in the tracking direction (Y direction).

On the other hand, a focusing drive permanent magnet 22 for applying a magnetic field to each of the focusing coils 20 is disposed on the actuator base 7 fixed to an optical head base (not shown). The focusing drive permanent magnet 22 is attached to a focusing drive yoke 23 fixed to the actuator base 7, and an opposing yoke 24 is provided inside the focusing coil 20. Further, a tracking drive solenoid 25 is disposed to face each of the tracking drive permanent magnets 21. The tracking drive solenoid 25 is attached to a tracking drive yoke 26 fixed to the actuator base 7. The actuator base 7 is made of a magnetic material and has a pair of focusing driving yokes.
A magnetic path connecting 23 and a magnetic path connecting the pair of tracking driving yokes 26 are formed orthogonally to each other, and each of the magnetic force lines generated by the focusing coil 20 and the tracking driving solenoid 25 is forced in a specific direction. , So that they can be effectively utilized individually.

Next, the operation of the objective lens actuator having the above configuration will be described.

During focusing control, the focusing coil 20
And the objective lens holder 2 is driven in the focusing direction by the electromagnetic force of the focusing coil 20 and the permanent magnet 22 for focusing drive. On the other hand, at the time of tracking control, a servo current flows through the solenoid 25, and the objective lens holder 2 is moved in the tracking direction by the attraction or repulsion of magnetic force generated between the solenoid 25 and the tracking drive permanent magnet 21 on the objective lens holder 2 side. Is driven.

Thus, the driving of the objective lens holder 2 (that is, the driving of the objective lens 1) is performed by the tracking drive permanent magnet 21.
The position of the objective lens holder 2 (that is, the position of the objective lens 1) can be detected by the method described below.

That is, during the tracking drive, the tracking drive mizuhisa magnet 21 attached to the objective lens holder 2
When the vehicle approaches or separates from the solenoid 25, an induced electromotive force is generated in the solenoid 25. By detecting this electromotive force with the voltmeter 27 connected to each solenoid 25, the position of the objective lens holder 2, that is, the tracking position of the objective lens 1 can always be detected. In this case, the tracking position of the objective lens holder 2 is obtained by detecting the amount of movement of the objective lens holder 2 based on the detected electromotive forces G ₁ and G ₂ of the solenoid 25 and accumulating the amount of movement.

In addition, the position signal of the objective lens holder obtained in this way is fed back to the solenoid 25, and a control circuit is provided to keep the objective lens holder 2 at the neutral position in the tracking direction, thereby always holding the objective lens holder 2 at the neutral position. In this state, the optical head can be driven for feeding. Therefore, it is possible to perform tracking control by driving the optical head itself, that is, by driving the objective lens actuator itself, and it is possible to perform tracking control by driving the objective lens actuator itself (driving the optical head itself) and driving the objective lens holder. A step servo system can be realized.

When the optical head accesses an arbitrary track on an optical disk or the like, the tracking servo is turned off and the optical head is driven for driving. At this time, at the moment when the tracking servo is turned off, the object detected by the solenoid 25 is detected. Objective lens holder 2 based on the signal of the lens holder position
When the relative position servo is applied to the solenoid 25 so as to maintain the neutral position, the objective track can be accurately accessed without the objective lens holder 2 being swung by the inertial force.

Further, when accessing the track, the swing of the objective lens holder 2 due to the inertial force can be suppressed without relying on the detection signal from the solenoid 25 as described above.

That is, when the track servo is turned off at the time of track access of the optical head, the polarity of the solenoid 25 is set to be the same as the polarity of the permanent magnet 21 on the solenoid 25 side. The objective lens holder 2 can be held at the neutral position by exerting the repulsive force of the direction, whereby the objective lens holder 2 can be suppressed from swinging in the tracking direction.

In the embodiment, the objective lens holder 2 is configured to be cantilevered by the four metal rods 4. However, the present invention is not limited to this. For example, the objective lens holder 2 may be supported by a plastic parallel plate spring. The present invention can also be applied to a formed objective lens actuator.

[Effects of the Invention] As described above, according to the present invention, a focusing coil and a permanent magnet for tracking drive are provided on an objective lens holder, and the permanent magnet for focusing drive and the solenoid for tracking drive on the actuator base side are used to drive an actuator. Since the focusing control and the tracking control are performed in the magnetic circuit having the base as the magnetic path, the focusing control and the tracking control can be performed by varying the generated magnetic field in the independent magnetic paths orthogonal to each other. Since each magnetic field line is forcibly applied to a magnetic path connecting the yoke and the actuator base, a large servo output can be obtained with a small magnetic force.
In addition, the induced electromotive force generated when the relative distance between the tracking drive permanent magnet and the tracking drive solenoid changes is measured by a voltmeter connected to each tracking drive solenoid. By accumulating the movement amount of the corresponding lens holder, the position of the objective lens holder, that is, the tracking position of the objective lens can be detected, and the tracking position signal of the objective lens is fed back to the tracking drive solenoid. As a result, it is possible to realize a two-step servo system in which the optical head is driven to feed while the objective lens is always held at the neutral position in the tracking direction, and the track servo is turned off when the optical head accesses an arbitrary track of the optical disk. Instantly, the polarity of the solenoid By making the same polarity as the polarity of the magnet on the solenoid side, a repulsive force is generated on both sides of the objective lens holder, and the objective lens holder can be held at the neutral position. Without this, an excellent effect is obtained such that the objective lens can access the target track at high speed and accurately.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an embodiment of an objective lens actuator for an optical head according to the present invention, FIG. 2 is a front view of the objective lens actuator shown in FIG. 1, and FIG. FIG. 2 is an exploded perspective view illustrating an example of an objective lens actuator of a head. DESCRIPTION OF SYMBOLS 1 ... Objective lens 2 ... Objective lens holder 3 ... Support base 7 ... Actuator base 20 ... Focusing coil 21 ... Permanent magnet for tracking drive 22 ... Permanent magnet for focusing drive 23 ... Yoke 25 for focusing drive …… Tracking drive solenoid 26 …… Tracking drive yoke 27 …… Voltmeter

Claims (1)

(57) [Claims] An object lens holder for holding an objective lens, a support for cantileverly supporting the objective lens holder so as to be displaceable in a focusing direction and a tracking direction, and a magnetic body for supporting the support, An actuator base on which a pair of tracking drive yokes facing each other in a direction and a pair of focusing drive yokes facing a direction substantially orthogonal to the tracking direction are provided, and the tracking direction of the objective lens holder is substantially equal to the tracking direction. A pair of focusing coils provided at both ends in a direction perpendicular to the direction, a pair of focusing drive permanent magnets disposed on the focusing drive yoke opposed to the pair of focusing coils, and the tracking direction of the objective lens holder. A pair of tigers provided at both ends A king driving permanent magnet, a pair of tracking driving solenoids disposed on the tracking driving yoke opposed to the pair of tracking driving permanent magnets, and a pair of tracking driving solenoids respectively provided for the pair of tracking driving solenoids. An objective lens actuator for an optical head, comprising: a voltmeter for measuring an induced electromotive force generated in each of the tracking driving solenoids at the time and detecting a tracking position of the objective lens.