JPS60234239A - Method and device for two-dimensional drive of objective lens - Google Patents

Abstract

PURPOSE:To attain the stable tracking servo by putting telescopically some of plural condition coils fixed to an objective lens on each other and setting them within a fixed magnetic field to obtain the excellent restoring force. CONSTITUTION:Coils 21 and 22 are set coaxially to the side face of a lens holder 2 of a tracking drive part 20. Some of these coils are put telescopically on each other and adhered. When current flows to both coils 21 and 22 in the direction shown in the figure, these coils receive magnetic fields M of different widths and directions. Therefore the restoring force is applied to both coils toward the balanced position. Thus the shift of an objective lens 1 due to the disturbance can be corrected. As a result, the lens 1 receives virtually no effect of the external force with a disk having no pregroup and even though the external force is applied with an opened tracking servo loop. This secures the stable tracking servo.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a two-dimensional driving device and driving method for an objective lens, and particularly to an optical information storage device, such as an optical disk device, a magneto-optical disk device, a digital audio device, etc. The present invention relates to a two-dimensional driving device and driving method for an objective lens that focuses a light beam onto a recording medium.

[Prior art]

Here, the following explanation will be given by taking an optical disk device as an example of an optical information storage device.

Generally, in an optical disk device, a width of 1~
Information bits of 2 μm and 1 to 3 μm in length are recorded. To read information from this information bit, first a light beam (usually a laser beam) is focused onto a minute spot (approximately 1 μm) using an objective lens, and is irradiated onto the information bit. At this time, the reflected light or transmitted light from the recording medium changes optically depending on the presence or absence of information bits. By detecting this change with a photodetector, a reproduced signal corresponding to the information bit can be obtained.

In this type of device, the objective lens used to focus the light beam has a large numerical aperture (NA), typically 0.
．． It has a value of 4 to 0.5. As is well known, as the numerical aperture increases, the depth of focus becomes shallower, typically ±2 μm.

In such an optical disk device, it is extremely important that the minute spot always accurately scan the information dot row on the recording medium-F. For this purpose, automatic adjustment is required to correct the focal shift caused by the curling of the recording medium, and autotracking is required to correct the deviation of the irradiation position due to the eccentricity of the recording medium.

Conventionally, as a method for realizing this autofocus function and autotracking function, a method is known in which an objective lens is supported by a spring-like structure and the effect of electromagnetic force caused by an electromagnetic coil and a magnet is utilized.

FIG. 1 is a plan view of a two-dimensional driving device for an objective lens using this conventional method, and FIG. 2 is a side sectional view.

The objective lens 1 is supported by an objective lens holder 2,
The upper and lower ends of the objective lens holder 2 are supported by leaf springs 3 and 4, respectively. The other ends of each of the leaf springs 3 and 4 are coupled via a relay plate 7 to the other ends of the leaf springs 5 and 6, each of which has one end fixed to a substrate. The coils 8 and 9 are fixed to the side surface of the lens holder 2, and the rigidity is increased by applying sufficient adhesive or the like. The magnetic field lines created by the yoke 11 , 12 and the permanent magnet 13 intersect the coil 8 . Similarly, yokes 14, 15, permanent magnet 16 and yokes 17, 18
, the magnetic lines of force created by the permanent magnets 19 also intersect the coils 9 and IO, respectively.

The coil 8 is a tracking coil, and a current corresponding to a tracking error signal flows therethrough, thereby displacing the position of the objective lens l in the direction of the arrow in FIG. In this way, tracking servo is performed to make the minute spot always follow the track on the disk surface.

On the other hand, the coils 9 and 10 are force-shinging coils, and the position of the objective lens 1 is moved in the direction of the arrow in FIG. 2 by flowing a current according to the focus error signal. In this way, focus servo is performed to maintain an appropriate distance between the objective lens 1 and the disk surface.

This method has the advantage that the autofocus operation is more stable than the autotracking method in which the optical beam is deflected at a small angle by rotationally driving a movable mirror, although this method does not cause optical axis misalignment.

However, when using a disk without a glue loop, the force that restricts the objective lens in the disk radial direction does not work much with the conventional drive device described above during recording, that is, when the tracking servo loop is open. become. As a result, the objective lens tends to sway in the disk radial direction due to external forces such as external vibrations, and the pitch r of the recording tracks becomes non-uniform. As a result, there was a drawback that the tracking servo during playback became unstable.

Therefore, it is necessary to always maintain a constant position by detecting the movement of the objective lens and controlling the position of the objective lens based on that information. For this reason, there are examples in which a capacitive position detecting means or a differential transformer is used as the position detecting means of the objective lens. However, all of them have the disadvantage of making the actuator larger and more expensive. Further, although the tolerance for movement of the objective lens varies depending on the value of the track pitch, it is generally ±0.5 μm or less. Detecting this degree of movement is extremely difficult due to signal noise and sensitivity. For this reason, it was necessary to use a disk with a grid loop.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned conventional drawbacks, and its object is to provide a two-dimensional driving device and driving method for an objective lens that stabilizes both an autofocus servo and an autotracking servo. It is in.

(6) [Summary of the Invention] In order to achieve the above object, the present invention is characterized in that a plurality of energizing coils fixed to an objective lens are partially stacked one on top of the other in a nested manner and provided within a constant magnetic field, Furthermore, the objective lens is fixed by energizing the energizing coils in different directions as necessary.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a plan sectional view of an embodiment of a two-dimensional driving device for an objective lens according to the present invention. However, since the objective lens, coil, and magnetic circuit portions are the same as those of the conventional example shown in FIG. 1, they will be omitted, and the same members will be given the same numbers and their explanation will be omitted.

In the tracking drive unit 20 shown in the figure, a coil 21 and a coil 22 are fixed to the side surface of the objective lens holder 2. The coil 21 and the coil 22 are arranged coaxially, and some of them overlap each other in a nested manner and are glued together, and lines of magnetic force are supplied from the yoke 12 to the overlapping part.

FIG. 4 is a perspective view of the tracking drive section 2o. In the figure, yoke 12 facing coils 21 and 22
The width a is set to be sufficiently wider than the normal width of the overlapping portion of the coils 21 and 22, so that sufficient lines of magnetic force can be supplied even when the coils 21 and 22 move.

Next, the operation of this embodiment having such a configuration will be explained using FIGS. 5 to 7.

FIG. 5 is a schematic cross-sectional view of the tracking drive section 2o for explaining the tracking function during information reproduction.

When reproducing information, current based on a tracking signal by known means is passed through the coils 21 and 22 in the same direction to perform tracking control. For example, if the coils 21 and 22 are energized in the direction of the arrow ■○C in the figure, the yoke 11
and 12, the coils 21 and 22 move in the direction of arrow B, allowing the light beam to follow the information track.

Next, when recording information, it is necessary to fix the objective lens 1. Therefore, as shown in FIG. 6, the same current is supplied to the coils 21 and 22 in opposite directions. For example, when a current flows in the direction of the arrow ■■ in the figure, the coil 22 receives a force in the direction of the arrow C due to the cooperation with the magnetic field M, and at the same time, the coil 21 receives a force in the direction of the arrow C due to the cooperation with the magnetic field M. The force is being applied in the direction of Therefore, the objective lens 1 is fixed at a position where forces in both directions are balanced.

The case where a disturbance is received in such a fixed state will be explained using FIG. 7.

Assume that the objective lens 1 moves in the direction of arrow E due to vibration of the apparatus or the like. Then, the width of the magnetic field M that the coil 22 receives decreases from G to H in the figure, and the force in the C direction that the coil 22 receives decreases. On the other hand, the width of the magnetic field M that the coil 21 receives increases from I to J in the figure, and the force in the D direction that the coil 21 receives increases. As a result, a restoring force acts on the coils 21 and 22 toward the mating position, correcting the displacement of the objective lens 1 due to disturbance.

Furthermore, the greater the deviation from the alignment of the objective lenses, the greater the restoring force, which improves the stability of recording with faster restoration response.

For example, since the response frequency can be secured at 5 kHz or more, the recovery time against disturbance is at most 2 x 10-' se
The bit error within this time can be sufficiently recovered by the error correction function during playback. Furthermore, this value is equivalent to the amount of errors occurring in the case of a pregroove disc.

As a result, even if an external force such as an external vibration is applied in any direction with the tracking servo loop open, the objective lens 1 will hardly be affected by it.

In this embodiment, an optical disk device is taken as an example, but the present invention is not limited to this, and can be applied to optical information storage devices in general such as magneto-optical disk devices and assotal audio devices, and furthermore, It can be applied to optical devices such as object shape inspection devices and flaw detection devices.

〔Effect of the invention〕

As explained above in detail, the two-dimensional driving device and driving method for an objective lens according to the present invention has an extremely excellent restoring force against disturbances, and even when a disk without a pregroup is used. Since the pitch of the recording tracks is uniform, this has the great effect of stabilizing tracking servo during reproduction.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are a plan view and a side sectional view, respectively, of a conventional two-dimensional driving device for an objective lens. FIG. 3 is a plan view of a two-dimensional driving device for an objective lens according to an embodiment of the present invention, FIG. 4 is a perspective view of a tracking drive unit in this embodiment, and FIG. FIG. 3 is a plan cross-sectional view of the tracking drive section for explaining the operation of the present embodiment. 1...Objective lens, 11.12...Yoke, 13.
...Permanent magnet, 20...Tracking drive unit, 21.
22...Coil @ (11) Fig. 1 7 Fig. 2 Shade 3 Fig. 5

Claims (3)

[Claims] (1) A two-dimensional driving device for an objective lens that drives an objective lens two-dimensionally and focuses a light beam on a predetermined position on an object, which has a magnetic field forming means that forms a magnetic field, and is fixed to a supporting member of the objective lens. A two-dimensional driving device for an objective lens, characterized in that a plurality of energized coils are arranged within the magnetic field. (2) The two-dimensional driving device for an objective lens according to claim 1, wherein the plurality of energizing coils partially overlap each other within the magnetic field. (3) In a two-dimensional driving method for an objective lens in which the objective lens is driven two-dimensionally and a light beam is focused on a predetermined position on an object, if necessary, the objective lens is fixed to a supporting member of the objective lens and placed in the same magnetic field. A two-dimensional driving method for an objective lens, characterized in that the objective lens is fixed by passing current through a plurality of arranged energizing coils in mutually different directions.