JPS63181128A - Objective lens driver - Google Patents

Abstract

PURPOSE:To attain small sized and thin profile optical pickup by providing a focus adjusting piezoelectric element and a track adjusting piezoelectric element linearly between a support member for an objective lens and a stationary member. CONSTITUTION:The objective lens 21 and a holder 23 including a support cylinder 22 are supported by the stationary member 26 via two piezoelectric elements (bimorph) 27, 28 connected and arranged linearly at an upper position from the face of the base 25. The voltage impressed state to both the piezoelectric elements 27, 28 is controlled to adjust the focus and track of the objective lens 21. The height of the entire device is lowered to miniature the device.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an objective lens driving device in an optical disk device called a so-called optical pickup.

Conventional technology In general, this type of optical disk device uses optical pickup (
It is important that the objective lens in the optical head (optical head) follow the track of the optical disc and be in focus. For this reason, various objective lens drive devices for focusing and track adjustment have been proposed and implemented in the past.

For example, there is one shown in Japanese Patent Application Laid-Open No. 58-222449. Its outline is shown in FIGS. 11 and 12. First, two rectangular vertical piezoelectric elements (bimorph)1.
1' connects the objective lens holding cylinder 3 holding the objective lens 2 and the movable piece 4. Also, similarly 2
The movable piece 4 and the base 6 are connected by a rectangular horizontal piezoelectric element (bimorph) 5.5'. Here, for convenience, the electrodes 7.1 and 5.5 of each of the piezoelectric elements 1.1' and 5.5' are shown with diagonal lines on the front and back sides. ．．
7', 8.8' are provided. As a result, when a voltage is applied to the electrodes 7, 7', the objective lens 2 is displaced in the tracking direction T perpendicular to the tracks on the optical disk due to the deformation of the piezoelectric elements 1, 1'. On the other hand, electrodes 8, 8
When a voltage is applied to ', the objective lens 2 is displaced in the focusing direction F perpendicular to the optical disc surface due to the deformation of the piezoelectric elements 5, 5'. In other words, piezoelectric elements 1 and i' are for track adjustment, piezoelectric elements 5 and 5' are for focus adjustment, and track adjustment and focus adjustment are possible by movement of the objective lens 2 in the T direction and F direction. It is what it is. In the drawings, reference numerals 9 and 10 are holes for laser beam transmission formed in the movable piece 4 and the base 6, respectively.

11 is a damper for the base 6 of the movable piece 4. Also, dampers 12, 12' are provided on both sides of the holding cylinder 3.

On the other hand, there is also one disclosed in Japanese Patent Laid-Open No. 61-45427. The outline is shown in FIG. First, a cylindrical holding frame 14 whose center axis is perpendicular to the base 13 is fixed on the base 13 . This holding frame 14 is provided with a support shaft 15 extending along the central axis. The second support shaft 15 has four radial bimorphs 16a to 16d.
It is supported by the holding frame 14 by. Furthermore, two strip-shaped bimorphs 17a and 17b extend from both upper and lower ends of the support shaft 15 in parallel with each other in the same direction. Specifically, it is in a horizontal state parallel to the base 13, and the upper and lower ends of an objective lens holding frame 19 containing an objective lens 18 are attached between the tips of these bimorphs 17a and 17b. In such a configuration, when a voltage is applied to the bimorphs 16a to L6d, the support shaft 15 and the bimorph 1 are connected to the bimorphs 16a to 16d.
Objective lens 18 connected via 7a and 17b
is due to the bending deformation of bimorph lea~16d.
- Displacement movement in the d direction. That is.

This is the track adjustment direction. On the other hand, bimorph 17a, 1
When a voltage is applied to 7b, these bimorphs 17a, 1
7b by bending displacement in the same direction.

The objective lens 18 is displaced in the direction of arrow e-f, that is, in the focusing direction. The combination of these movements results in
Track adjustment and focus adjustment of the objective lens 18 are performed.

Problems to be Solved by the Invention However, in the case of the former method disclosed in Japanese Unexamined Patent Application Publication No. 58-222449, the track adjustment piezoelectric element l.

The portion that performs the bending movement 1' is located below the objective lens 2 when viewed from the optical disk, which increases the height of the entire apparatus. Therefore, it is not suitable for downsizing the device.

On the other hand, in the case of the latter method disclosed in JP-A-61-45427, it is necessary to support the support shaft 15 with respect to the holding frame 14 by a plurality of bimorphs 1ea-16F. For this reason, the structure becomes complicated, resulting in poor productivity.

Means for Solving the Problems In order to convert signals recorded on the optical disk into optical signals, an objective lens for focusing a laser beam onto the optical disk is orthogonal to the track of signal bits on the optical disk. In an objective lens drive device that moves in a tracking direction and a focusing direction perpendicular to the optical disk surface, a piezoelectric element for focus adjustment of the objective lens and a piezoelectric element for track adjustment are provided between a holding cylinder that holds the objective lens and a fixed member. and arranged in a straight line.

The working objective lens, the piezoelectric element for focus adjustment, the piezoelectric element for track adjustment, and the fixing member are linear and planar, and the height in the focus direction is thin.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. First, the holding cylinder 22 that holds the objective lens 21
is provided. This holding cylinder 22 is rotatably supported by a pin 24 with respect to a holder 23 which is approximately semicircular in plan view.

This means that even if the objective lens 21 moves up and down with respect to the base 25 surface by the focus adjustment actuator (even if the holder 23 is tilted), the objective lens 21 and the base 25
In order to ensure parallelism with pin 5, the holding cylinder 22 is attached to this pin 2.
It is set so that it rotates around 4 and always maintains a vertical position due to its own weight.

Here, a block-shaped fixing member 2 is provided on the base 25.
6 is provided. Then, the objective lens 21. The holder 23 including the holding cylinder 22 is supported by the fixing member 26 at a position above the surface of the base 25 via two piezoelectric elements (bimorphs) 27 and 28 connected and arranged in a linear manner.

These piezoelectric elements 2'7 and 28 are connected by a connector 29, and the displacement directions are set in different orthogonal directions. That is, the piezoelectric element 27 on the fixed member 26 side is used for focus adjustment, whereas the piezoelectric element 28 on the holder 23 side is used for track adjustment. Thereby, the objective lens 21 (holding cylinder 22) is supported so as to be movable in the focus F direction and the track direction T. For example, the piezoelectric element 27 is of a symmetrical type whose polarization is symmetrical with respect to the intermediate electrode, and the front and back sides thereof have electrodes 30a as shown with diagonal lines in FIGS. 2 and 3 for convenience.

30b is formed. Therefore, these electrodes 30
If a voltage is applied between a and 30b, this piezoelectric element 2
6 is displaced in the direction shown by arrow F in FIG. 1, so that it can function as an actuator for adjusting the focus of the objective lens 21. The same applies to the piezoelectric element 28, electrodes 31a and 31b are formed on both the left and right sides of the piezoelectric element 28, and when a voltage is applied between the electrodes 31a and 31b, the piezoelectric element 28 is displaced in the downward direction of the arrow, so that the objective lens 21
This means that it can function as an actuator for track adjustment. In other words, the piezoelectric element 27. ．． Focus and track adjustment of the objective lens 21 is made possible by controlling the voltage application state to both of the objective lenses 28 and 28. Note that a light transmission hole 32 is formed in the base 25 at a position facing the objective lens 21.

Incidentally, in an optical disc memory device using this type of optical pickup, the eccentricity of the disc is approximately ±70 μm, and the disc surface runout is approximately ±0.4 mm.

On the other hand, the focus adjustment actuator side absorbs the disk surface runout, and the track adjustment actuator side absorbs the disk eccentricity. In other words, the former adjustment displacement amount needs to be larger than the latter adjustment displacement amount. It is well known that the displacement of a piezoelectric element (bimorph) increases as its length in the direction perpendicular to the polarization direction increases. In this regard, according to this embodiment, the focus adjustment piezoelectric element 27 is required to have a large amount of adjustment displacement, as shown in the drawings.
is the fixed member 26 side, that is, the objective lens 21 to be displaced.
Since the track adjustment piezoelectric element 28 is placed away from the lens 21 and on the objective lens 21 side, it is easy to adjust the amount of displacement in the direction of the focus F to a large extent.

In any case, according to this embodiment, the piezoelectric elements 27 and 28 constituting the actuator for adjusting the focus and track of the objective lens 21 are arranged linearly between the objective lens 1 side and the fixed member 26 side. Therefore, the height in the focus direction can be lowered to make the optical pickup smaller and thinner. Furthermore, it is simple in terms of structure because it is sufficient to provide two piezoelectric elements 27 and 28 and connect them.

In addition, in this example, piezoelectric elements 27 and 28 with symmetrical polarization are used.
Although the description has been made using a bimorph with asymmetric polarization, it is also applicable to a unimorph.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, it is assumed that the focus error is small and the tracking error is large.
The piezoelectric element 28 for track adjustment is placed on the side of the fixing member 2.
It is arranged on the 6th side. According to this, track adjustment by the piezoelectric element 28 can be efficiently performed in a state where a large amount of displacement can be obtained.

Further, a third embodiment of the present invention will be explained with reference to FIGS. 5 and 6. In this embodiment, instead of the piezoelectric element 27, connector 29, and piezoelectric element 28 as shown in FIG. By twisting, half of the piezoelectric element 34 is used for focus adjustment, and the other half is used as a piezoelectric element 35 for track adjustment. It is also clear from this that both piezoelectric elements 34 and 35 are linearly arranged.

Here, the structure of the piezoelectric element 33 will be explained. In this embodiment, an asymmetric bimorph is used, and a piezoelectric element material 33b has a metal plate 33a sandwiched in the center and the polarization direction is set as shown in FIG.

33c. And piezoelectric element 3
Electrodes are formed on the front and back sides of 3, including focus electrodes 36 a, 36 b and track electrodes 37.
a and 37 b are formed separately.

Even with such a configuration, the operation is similar to that of the embodiment described above. According to this embodiment, since the actuator requires only one piezoelectric element 33, the connector 29 is not required, and the weight is reduced accordingly.

As a result, the driving force for the piezoelectric elements 34 and 35 only needs to be small, and the response characteristics are also improved.

Although this example uses an asymmetric bimorph, it is also possible to use a symmetric bimorph as in the example described above.

Furthermore, a fourth embodiment of the present invention will be explained with reference to FIGS. 7 to 1O. In this embodiment, the piezoelectric element for focus adjustment in the previous embodiment is constituted by two piezoelectric elements 34a and 34b having the same characteristics. More specifically, these piezoelectric elements 34a and 34b are cut into two parts up to the center in the longitudinal direction of one piezoelectric element 33, and in this state, each piece is twisted by 90'' in the same manner as in the previous embodiment. In the initial state without deformation, both are set parallel to the base 25.

The reason why the focus adjustment piezoelectric element side is configured with two elements will be explained. First, as shown in FIG. 9, a case will be considered in which focus adjustment is performed using a piezoelectric element 33 similar to that in FIG. 5. In this case, it is assumed that the holder 23 and pin 24 are not present in the holding tube 22 for the objective lens 21 and are directly connected to one end of the piezoelectric element 33. Here, the electrodes 36 a, 36 of the focus adjustment piezoelectric element 34
In the initial state where no voltage is applied to b, Fig. 10(a)
As shown in FIG.
5), and the central axis φ8 of the objective lens 21 and the optical axis φ. are coincident or parallel.

Then, when a voltage is applied to the electrodes 36a, 36b, the piezoelectric element 34 is deformed in the focus direction as shown in FIG. 10(b) or (C) depending on the polarity. In this case, the piezoelectric element 34 is displaced in an arc shape around the fixing member 26 (the connector 29 in the case of the system shown in FIG. It will change. As a result, objective lens 2
The central axis φ of 1 is the optical axis φ as shown in FIG. 10(b) or (C). is no longer parallel to . In other words, it is no longer perpendicular to the base 25, making accurate recording and reproduction impossible.

In this regard, from a structural point of view, if the holding cylinder 22 is supported by the holder 23 via the pin 24 as described in the first embodiment, it can be maintained in a vertical state. However, in this embodiment, the central axis φ of the objective lens 21 is prevented from falling by using a simple direct-coupling structure that does not use such a pin 24 or the like.

The operation during focus adjustment according to this embodiment will be explained with reference to FIG. First, FIG. 8(a) shows an initial state in which no voltage is applied to any of the electrodes 36a, 36b of the focus adjustment piezoelectric elements 34a, 34b. In this state, the central axis φ of the objective lens 21 and the optical axis φ. are in a state of coincidence or parallelism. And a focus adjustment piezoelectric element 34
When the same voltage is applied to both electrodes a and 34b, 2
The piezoelectric elements 34a, 34b are movably displaced in a parallelogram state as shown in FIG. 8(b) or (C) depending on their polarity. In other words, it is not a rotational displacement but a vertical displacement with respect to the base 25. Therefore, the objective lens 21 held on the open end side of the piezoelectric element 33 also moves perpendicularly to the base 25. As a result, as shown in FIG. 8(b) or (c), the central axis φ1 of the objective lens 21 is the optical axis φ. It is always displaced in the focus direction in a parallel state. As a result, the optical axis φ. Since the amount of deviation from
Accurate recording and playback becomes possible. Therefore, according to this embodiment, the piezoelectric element 33 is directly connected to the holding tube 22 in a simple configuration, and it is possible to prevent the axis of the objective lens 21 from tilting during focus adjustment.

Note that two piezoelectric elements for focus adjustment as in this example are used.
In the method of configuring the connector 2 as in the first embodiment,
Needless to say, the present invention can be similarly applied to a method in which the structure is connected by 9. Further, the same applies to those arranged not on the fixed member 26 side but on the objective lens 21 side.

Effects of the Invention As described above, the focus adjustment piezoelectric element and the track adjustment piezoelectric element constituting the focus and track actuator of the objective lens are arranged linearly between the objective lens holding member and the fixing member. Since the actuator members are arranged in parallel, the thickness of the actuator member in the focus direction does not increase, and the optical pickup can be made smaller and thinner.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing a first embodiment of the present invention, and FIG.
The figure is a front view, FIG. 3 is a plan view, FIG. 4 is a schematic perspective view showing a second embodiment of the present invention, FIG. 5 is a schematic perspective view showing a third embodiment of the present invention, and FIG. 7 is a schematic perspective view showing a fourth embodiment of the present invention, FIG. 8 is a front view showing a deformed state during focus adjustment operation, and FIG. 9 is a schematic perspective view, FIG. 10 is a front view showing a deformed state during focus adjustment operation, FIG. 11 is a perspective view showing a conventional example, FIG. 12 is a front view thereof, and FIG.
The figure is a perspective view showing a different conventional example. 21... Objective lens, 22... Holding tube, 26...
Fixing member, 27... piezoelectric element for focus adjustment, 28
...Piezoelectric element for track adjustment, 34.34a, 34b
...Piezoelectric element for focus adjustment, 35...Piezoelectric element for track adjustment ~ %Ll-Figure, 3J 5 Figure-To Koga, l, I to door (Kuratsu 1 sword Z diagram (confessional υ) U north exit (Shiken S)

Claims (1)

[Claims] An objective lens that focuses a laser beam onto the optical disk in order to convert signals recorded on the optical disk into an optical signal is arranged in a tracking direction perpendicular to the track of signal pits on the optical disk and perpendicular to the surface of the optical disk. In the objective lens driving device for moving the objective lens in a focusing direction, a piezoelectric element for focus adjustment and a piezoelectric element for track adjustment of the objective lens are arranged linearly between a holding cylinder that holds the objective lens and a fixing member. An objective lens drive device featuring: