JPS61289542A - Optical head actuator - Google Patents

Abstract

PURPOSE:To miniaturize an optical head by adopting the constitution that a special condition exists between a distance from a pseudo center to a point where the optical axis and the optical reflecting face are changed and a distance from a focus of an objective lens to a point where the optical axis and the optical reflecting face are changed. CONSTITUTION:The pseudo turning center 0' different from the existing center 0 is set to drive the optical reflection face accessing a beam as if the face were turned around the pseudo turning center 0' as the turning center. In this case, the distance (a) from the pseudo turning center 0' to a point P where the optical reflection face crosses the lens optical axis U and a distance (l) from the focus F to the point P are designed to have a relation of 1=2<1/2>.l. Since the light beam is made incident vertically on a disc face in the optical head actuator, the polarization of the light beam is avoided and no beam shift is caused. Thus, a galvano mirror having very small beam shift quantity is realized and remarkable miniaturization is attained even when the galvano mirror is combined with a focus actuator.

Description

[Detailed Description of the Invention] [(Summary)] The optical head actuator of the present invention includes a galvano mirror.
By improving the relative positional relationship between the light reflecting surface and its rotation axis, the beam shift amount is large, which is a problem common to conventional actuators.

■If the above-mentioned beam shift is difficult to occur, the size will become huge.

This was done to solve the problem.

[Industrial application field]

Recent optical disk devices are particularly geared towards being smaller and lighter, and for this reason, efforts are being made to simplify the structure of the optical head actuator and rationalize it by reviewing the layout of each component.

TECHNICAL FIELD The present invention relates to an improvement in an optical hemlock actuator installed in an optical disc device.

[Conventional technology]

Beam access using a conventional galvanometer mirror will be explained with reference to FIG. 9 and FIG. 1O.

FIG. 9 is a beam access operation diagram using a conventional galvano mirror, and FIG. 10 is a perspective view showing the structure of a conventional galvano mirror.

In these figures, 2 is a light reflecting surface rotating wheel, 3 is an objective lens, 4 is a coil, 5 is a magnetic circuit, F is a focal position of the objective lens, U is a lens optical axis, and l is a direction from the focal position to the optical axis and light. The distance to the point P where the reflection surface intersects with the reflection surface, 0 indicates the center of rotation of the reflection surface.

As shown in FIGS. 9 and 10, the galvanometer mirror 10 controls the rotation angle θ of the light reflecting surface 1 by the amount of current flowing through the coil 4. As shown in FIGS.

However, as shown in Figure 9, the conventional galvano mirror
10, a beam shift E is caused by accessing the light beam 7.

For example, if we calculate the beam shift amount E when accessing the disk with the disk eccentricity δ・0, 05+a+o, it will be about 0.23 mm when the optical system is configured with a commonly used objective lens, and the beam shift amount E when accessing the disk will be approximately 0.23 mm. Naturally, the light returned from the disk 15 will also move. This becomes an offset amount of the trunk error signal and causes deterioration of the followability of the trunk.

However, in the above configuration, it is also possible to adjust the relative position between the galvanometer mirror 10 and the objective lens 3 so that beam shift does not occur, and the conditions for this are shown in FIG.

The condition is to position the center of rotation 0 of the light reflecting surface so that the relationship between the distance a between 0 and P and the distance i between F and P in FIG. By taking this measure, the reciprocating optical paths of the beam 7 are matched (the beam 7 is incident perpendicularly to the disk surface of the optical disk 15), so that no beam shift occurs.

The reason is based on the calculation formula below.

cos (θ+π/4) tan2θ1, °, a = fTl Figure 6 is a perspective view showing an example of the shape of the objective lens, and in this example, the diameter d of the objective lens 3 is approximately 6.51) 1) 1
). Similarly, the height h' is approximately 4 mm, and the focal length f is approximately 2III m, so miniaturization has already been achieved.

[Problem that the invention seeks to solve]

However, as shown in FIG. 7, there is a coil 4 surrounding the objective lens 3. Magnetic circuit 5. Since the various members such as the leaf spring 8 that support the objective lens are arranged on the base 9, if the structure shown in FIG. The total height H becomes extremely high, 34 to 36III1). Incidentally, the height H” of the focus actuator is approximately I
OI is 1m.

Furthermore, since the length l' corresponds to the length of the optical head from the objective lens 3 toward the center of the disk 15, if this dimension is large, the optical head will not be able to enter the inner side of the disk 15.

This is a very disadvantageous condition from the viewpoint of effective use of the disk surface.

The present invention aims to provide means for solving the above-mentioned problems that are considered to be disadvantageous to optical head actuators.

[Means for solving problems]

The above problem is almost equivalent to the case where the pseudo rotation center 0° is set at a different position from the actual center O, and the light reflecting surface that accesses the beam is driven around the pseudo rotation center O°. The above results are solved by the optical head actuator of the present invention.

In the case of the present invention, the distance a from the pseudo rotation center O' to the point P where the light reflecting surface intersects the lens optical axis U, and the distance β from the focal position F to the point P are a=r d·l. In addition, the structure is such that there is no need to provide an actual center of rotation around the objective lens, where magnetic circuits, coils, etc. are densely packed.

[Effect]

Therefore, in the optical head actuator of the present invention, the light beam is perpendicularly incident on the disk surface. Therefore, the polarization phenomenon of the light beam is avoided, and no beam shift occurs.

Further, the present invention does not require providing an actual center of rotation around the objective lens where magnetic circuits and the like are densely packed, so that the optical head can be made smaller.

〔Example〕

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

FIG. 1 is a diagram showing the principle of the present invention, and the same reference numerals as in each of the figures used in the explanation up to now indicate the same parts.

0 in the figure is the actual rotation center of the light reflecting surface 1, points A and B are two points on the light reflecting surface 1 located at different distances from 0, and ∠AOB is a value smaller than 90''. It is set so that

The light reflecting surface 1 is indicated by A and B, and the minute angle to be combined When this light reflecting surface 1 rotates, the points A and B rotate around the pseudo center 0゛ and reach the points A' and B''. I can see it.

Therefore, if the length in the figure is 0'P -a, then a-f''r
If 1 is satisfied, no beam shift will occur as explained in FIG.

FIG. 2 is a configuration diagram of a galvanometer mirror to which the present invention is applied.

In the figure, 4 is a coil, 5 is a magnetic circuit, 1 is a light reflection surface, and 2 is a mirror rotation wheel. By energizing the coil 4, the light reflection surface 1 is moved in the vertical direction around the rotation axis 2. The light beam 7 is rotated to scan the light beam 7. Incidentally, the height h of the galvanometer mirror 10 is approximately 10 mm.

FIG. 3 is a diagram showing an example of actual calculation.

For example, if l = 14.65 mm, a
=20.72mm, and at this time OP -29,5n
It becomes v+. However, when actually performing servo using the galvanometer mirror, there are factors that cause the above relationship a=f1 to be broken. (1) Movement of the focus position F caused by movement of the focus actuator in the focus direction.

■The pseudo center O゛ of the light reflecting surface of the present invention moves slightly depending on the rotation angle (.

■Error during actuator assembly.

etc., but due to these causes a = 7″′T1
When this relationship is no longer maintained, it appears as a beam shift during track access.

Assuming that the amount of deviation from a--"Tβ caused by these factors is 0.5 mm from the above (1), 0.17 mm from (2), and 0.3 mm from (2), the total will be 0.97 mm.

Therefore, in order to compare with the conventional galvano mirror, the beam shift amount E''-0.03 mm is calculated by substituting the above 0.97 mm for l in Fig. 9. This value is compared with the case of the conventional galvano mirror. By comparison, it can be seen that in the case of the present invention, the beam shift amount is about 18.

FIG. 4 is a perspective view showing a modification of the present invention, showing the front seventh
Focus actuator and galvano mirror shown in the diagram
This shows an example of a structure in which the two are integrated.

With this configuration, the total height H of the actuator is approximately 2
0 mm, and the value l', which determines how far the actuator can penetrate into the inner side of the disk, is about 8 mm, making it possible to significantly reduce the size of the actuator compared to conventional actuators.

〔Effect of the invention〕

According to the present invention, the galvanometer mirror has a much smaller beam shift amount during track access than conventional ones.
can be realized, and even when combined with a focus actuator, it has the great effect of enabling revolutionary miniaturization.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of a galvano mirror according to the present invention, Fig. 2 is a configuration diagram of a galvano mirror to which the present invention is applied, Fig. 3 is a schematic diagram showing a calculation example of a galvano mirror according to the present invention, and Fig. 4 is a diagram of the galvano mirror according to the present invention. A perspective view showing a modification of the invention, FIG. 5 is a configuration diagram of a galvano mirror in which no beam shift occurs, FIG. 6 is a perspective view showing the shape of an objective lens, FIG. 7 is a structural diagram of a focus actuator, and FIG. 8 9 is a schematic diagram of an optical head, FIG. 9 is a diagram of a beam access operation using a conventional galvano mirror, and FIG. 10 is a perspective view showing the structure of a conventional galvano mirror. In the figure, 1 is a light-reflecting surface, 2 is a light-reflecting surface drive wheel, 3 is an objective lens, 4 is a coil, 5 is a magnetic circuit, 7 is a beam, 8 is a temporary spring, 9 is a base, 10 is a galvanometer mirror (1) 5 is the disk, h is the height of the galvanometer mirror, H is the total height of the actuator, d is the diameter of the objective lens, h゛ is the height of the objective lens, h'' is the height of the focus actuator, f is the height of the objective lens. Focal length, E is the amount of beam shift, 0 is the rotation center of the light reflecting surface, 0' is also the pseudo center, F is the image side focal position of the objective lens, P is the point where the optical axis and the light reflecting surface intersect, θ
is the rotation angle of the light reflecting surface, a is the distance from the pseudo center to the point where the optical axis and the light reflecting surface intersect, l is the distance from the image side focal position to the point where the optical axis and the light reflecting surface intersect, l゛ is the distance between the optical axis of the objective lens and the pseudo center, U is the optical axis of the objective lens, and A and B are arbitrary two points on the light reflecting surface that are at different distances from the rotation center O of the light reflecting surface, respectively. show. 4%+o small-yo armor"z ha't Sler's lhiJsibiheQts I
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Claims (1)

[Claims] An optical head actuator that is disposed in an optical disk device and is equipped with a galvano mirror (10) for reading and writing information on the disk and an objective lens (3), the galvano mirror (10) comprising: The angle ∠ between the center of rotation O of the light reflecting surface (1) and any two points A and B on the light reflecting surface (1) located at different positions from the center O
AOB maintains a relationship such that ∠AOB≦90°, and the light reflecting surface (1) and the optical axis U of the objective lens (3) intersect with each other at an angle of 45°, and the light reflecting surface (1) When rotates around O, the light reflecting surface (1)
The pseudo center of the light reflecting surface formed in the space between , objective lens (
If the distance from the focal point F in 3) to the point where the optical axis U intersects with the light reflecting surface (1) is l, then the relationship between a and l is such that a=√2l. Features of optical head actuator.