JPH0471270B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention records information on the surface of a recording medium using optical means, or reproduces or erases information already recorded on the surface of the recording medium. The present invention relates to a lens actuator for an optical head, and more particularly to a lens actuator that moves a condenser lens perpendicularly and parallel to the surface of a recording medium.

[Conventional technology]

Conventionally, optical technology uses laser light as a light source and modulates the laser light with pulsed signals from an external information source to record binary information on the surface of a recording medium, or to reproduce or erase information that has already been recorded. In order to accurately record, reproduce, or erase information, the head uses a lens actuator to control the focal position in the focus direction so that the surface of the recording medium is the focal point of the condensing lens. At the same time, the condenser lens is installed so that the light spot of the focused laser beam on the recording medium surface is accurately positioned with respect to the guide groove formed in advance on the recording medium surface. Tracking position control is performed by driving in a tracking direction perpendicular to the guide groove.

Various configurations have been proposed for this type of lens actuator, one of which is one in which movable support in the focus direction is provided by a parallel plate spring, and movable support in the tracking direction is provided by a swing support mechanism. There is. For example, the lens actuator proposed in Japanese Patent Application No. 58-199504 corresponds to this. The most basic configuration of this type of lens actuator is as follows. The movable part equipped with the condensing lens is attached to the arm via two leaf springs in a direction perpendicular to the focus direction. Further, the arm is held by a swinging support mechanism on the sliding body so as to be swingable in the tracking direction. Further, in order to drive the movable part in the focusing direction and the tracking direction, a focus coil and a tracking coil are provided in the movable part. The focus coil is wound below the parallel leaf springs and so as to surround the optical axis of the condensing lens mounted on the movable part, and the tracking coil is wound on the movable part between the parallel leaf springs. The center of gravity is set at the position that drives the center of gravity.

[Problem that the invention seeks to solve]

In the conventional lens actuator described above, due to the relationship between the rigidity of the leaf spring and the mass of the movable part,
Vibration in the rotational direction about the longitudinal axis, which is perpendicular to the torsional direction of the movable part, that is, the tracking direction and the focusing direction, is unavoidable. Vibration in this direction results in the light spot caused by the condensing lens vibrating in the tracking direction, and since vibration in this direction is a rotational movement that cannot be controlled by the actuator in the tracking direction, the movement of the condensing lens in the tracking direction is The servo band is limited by the resonance frequency of the torsional vibration of the movable part including the condenser lens. As a result, there is a drawback that the movable part including the condenser lens cannot operate at high speed. In addition, the value of the resonant frequency of the leaf spring that supports the movable part is sensitive to its length in the longitudinal direction. It goes without saying that the characteristics of the actuator must be adjusted, but there are also drawbacks such as variations in characteristics between individual actuators, resulting in poor characteristics.

The purpose of the present invention is to eliminate such drawbacks, increase the resonance frequency of the torsional vibration of the movable part including the condensing lens, realize high-speed operation, and provide a lens with dynamic characteristics with small individual differences in characteristics. The purpose of this invention is to provide an actuator.

[Means for solving problems]

The lens actuator of the present invention includes a movable part equipped with a condensing lens that condenses light from a light source onto the surface of a recording medium, an arm, and one end of the movable part on both sides in the tracking direction and above and below in the focus direction. A flanged spring portion is provided at three locations at both ends and an intermediate portion thereof, and is provided with flanges parallel to a longitudinal direction perpendicular to the tracking direction and the focusing direction of the movable portion, and is connected to the movable portion. a plurality of leaf springs movable in the focus direction, each having a structure in which flexible parts are provided between the flanged spring part connected to the arm, the flanged spring part joined to the arm, and the intermediate flanged spring part; a swing support mechanism that supports the arm on a body so as to be able to swing around one axis parallel to the focus direction; a cass coil and a tracking coil; and a condensing lens provided on the housing.
It is characterized by having two magnetic circuits magnetically coupled to the focus coil and the tracking coil on both sides in a direction perpendicular to the tracking direction.

[Effect]

The lens actuator of the present invention reduces the moment of inertia of the movable part in the longitudinal direction perpendicular to the movable part focus direction and the tracking direction, which determines the resonance frequency of the torsional vibration of the movable part, and at the same time supports the movable part. By creating a structure in which the rigidity of the leaf spring is increased, the resonant frequency of the torsional vibration of the movable part can be set high, and at the same time, the desired designed dynamic characteristics can be realized with high precision. That is, according to the configuration of the present invention, since the focus coil is set between the parallel plate springs, the movable part does not become elongated in the focus direction, and therefore, the moment of inertia around the longitudinal direction can be set small. . The plurality of leaf springs installed between the movable part and the arm are attached to the flange attached to the leaf spring, except for the flexible part sandwiched between the flange attachment part in the intermediate part and the vicinity where it is joined to the movable part and the arm. The rigidity is increased by Due to the synergistic effect of the above two effects, a lens actuator that is lightweight and highly rigid and has a high torsional resonance frequency can be obtained, and high-speed operation in the tracking direction can be realized. In addition, by setting the leaf spring as in the configuration of the present invention, the length of the flexible part and the boundary conditions with the flanged spring part, which most affect the dynamic characteristics of the movable part, can be kept constant because it is an integral part. The dynamic characteristics of the movable part can be made to closely match the design values, and the error between the design values and the actual characteristics can be greatly reduced.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

1 and 2 show a first embodiment of the present invention, with FIG. 1 being an exploded perspective view and FIG. 2 being a perspective view. For convenience of explanation, an orthogonal Cartesian coordinate system is set in FIG. The x-coordinate direction indicates the tracking direction, and the z-coordinate direction indicates the focus direction.

The lens actuator of this embodiment includes a condenser lens 1, a focus coil 8, a tracking coil 9, a movable part 2, and leaf springs 3a, 3a', 3.
b, 3b', the arm 4, the rotation support mechanism 5, the center yokes 10a, 10b, the magnets 11a, 11b provided on the body 6, and the side yoke 1.
2a and 12b.

The condensing lens 1 condenses laser light from a light source onto the recording medium surface.

The movable part 2 is equipped with this condensing lens 1. Two holes 13a and 13b are formed in the movable part 2 at positions on both sides of the condenser lens 1 in the focus direction (y coordinate direction) perpendicular to the tracking direction (x coordinate direction). so as to surround these two holes 13a, 13b and the condenser lens 1.
A focus coil 8 is wound parallel to the xy plane. Furthermore, four tracking coils 9 are connected to the focus coil 8. The tracking coil 9 is a coil wound into a thin, almost rectangular donut shape, and is arranged so that current mainly flows in the focus direction on one side of the coil in a portion corresponding to the y-coordinate direction of the holes 13a and 13b. There is.

The leaf springs 3a, 3a', 3b, and 3b' support the movable part 2 with respect to the arm 4, and in this embodiment, the movable part 2 on which the condenser lens 1 is mounted is aligned in the tracking direction (x coordinate direction). ) The lower surface of one end of the leaf springs 3a, 3b and the inner surface of the flange portion are respectively joined to the upper surface and side surface of the upper protrusion at both ends, and the leaf springs 3a', 3a', The upper surface of one end portion and the inner surface of the flange portion of 3b' are respectively attached. These four leaf springs 3a, 3b, 3a', 3b' are installed parallel to the y-coordinate direction.

The lower surface of the other end of the leaf spring 3a and the inner surface of the flange portion, and the lower surface of the other end of the leaf spring 3b and the inner surface of the flange portion,
The leaf springs 3a' and 3b' are attached to the upper surface and the side surface of the arm 4, respectively. At that time, leaf spring 3a and leaf spring 3
a' and leaf spring 3b' of leaf spring 3b are set to be parallel to each other. The movable portion 2 is movably supported in the focus direction (z-coordinate direction) by these four leaf springs 3a, 3b, 3a', and 3b'.

The structure of these leaf springs will be explained in detail with reference to FIGS. 3 and 4.

FIG. 3 is a typical perspective view for explaining the structure of the leaf spring 3a in detail, and FIG. 4 shows a cross-sectional shape taken along the cross-section x shown in FIG.

In FIG. 3, p, q, r, s, t, u, v, and w each indicate the position in the longitudinal direction (y coordinate direction) of the leaf spring. The leaf spring has a simple flat plate structure in the range from position r to s and from position t to u, can be easily bent in the focus direction (z coordinate direction), and from position p to q and from v to w. In the range, the leaf spring 3a is connected to the movable part 2 shown in FIG.
It is joined to the arm 4 including flanges 14 and 16. On the other hand, between position s and t, flange portions 1 are provided on both sides parallel to the longitudinal direction of the flat spring.
5, 15' are formed, and as a result, the cross-sectional shape cut at the cross-section x becomes a U-shape as shown in FIG. Therefore, in this structure, the bending rigidity is low from position r to s, from position t to u, and the bending rigidity is high from position q to r, from s to t, and from u to v, and the focus direction of the movable part 2 is To cope with the displacement by bending the flat spring from position r to s and from position t to u, and to have a structure with high rigidity against torsional displacement due to the effect of flanges 15 and 15' in the center. I can do it. At the same time, by using the leaf spring of this embodiment, the size of the flexible part that undergoes deformation when the movable part deflects in the focus direction is reduced compared to the conventional simple leaf spring that connects the movable part and the arm part. However, the design can be maintained even after assembly. In other words, if springiness is applied to the joint boundary between the movable part and the arm as in the past, the joint strength, effective joint length, etc. will vary depending on the individual product, resulting in changes in the dynamic characteristics of the movable part. This can be avoided in this embodiment because the flexible part realizes the design value.

The swing support mechanism 5 is a mechanism capable of swinging around an axis 7 parallel to the focus direction (z-coordinate direction). The swing support mechanism section 5 includes four leaf springs 3.
A, 3b, 3a', 3b' are attached to the opposite side of the arm 4, and the arm 4 is fixed to the swing support mechanism. The swing support mechanism 5 supports the arm 4 so as to be swingable about an axis 7 parallel to the focus direction (z-coordinate direction) with respect to the body 6. Therefore, the movable part 2 is movably supported also in the tracking direction (x-coordinate direction).

The magnetic circuit includes center yokes 10a, 10b, magnets 11a, 11b, and side yokes 12a, 12.
b, and is installed on the body 6. Center yokes 10a and 10b have holes 13
a, 13b, and one side of the tracking coil 9 and a part of the focus coil 8 are located in the gap of the magnetic circuit.

A magnetic flux is generated in the y-coordinate direction by a magnet in the gap of the magnetic circuit, and as a result, the movable part 2
By applying a current to the focus coil 8, it is driven in the focus direction (z coordinate direction), and by applying a current to the tracking coil 9, it is driven in the tracking direction (x coordinate direction), and the focus direction and the focus direction of the condenser lens 1 are driven. A movement is made in the tracking direction.

According to the configuration described above, first, since the focus coil 8 is located between the upper and lower leaf springs, the movable part 2 is shortened in the focus direction, and as a result, the moment of inertia of the movable part 2 in the torsional direction of the leaf spring is reduced. Can be made smaller. In addition, the stiffness distribution of the leaf spring is made soft in the vicinity where it is joined to the movable part 2 and the arm 4, and by providing a flange on the leaf spring in the middle to make it stiff, it is soft in the focus direction and is soft in the torsional direction. can be rigid. Due to these synergistic effects, the resonance frequency of the torsional vibration of the movable part 2 can be set high. In addition, flanges are provided at the ends of the joints of the leaf spring with the movable part 2 and the arm 4 to increase rigidity, and the flexible part sandwiched between these high-rigidity parts and the intermediate flanged part has spring properties. By adopting a structure that allows the flexible portion to have a uniform size, the size of the flexible portion can be set precisely, and therefore the spring characteristics of the flexible portion can be uniform, and the vibration characteristics can be made uniform.

In addition, since the movement of the condensing lens 1 in the tracking direction is supported by oscillating support, the arm 4
There is no need for the plate spring to operate in the same way as the movable part 2, and the structure is such that no unreasonable force is applied to the leaf spring to induce torsional vibration.

The driving force of the focus coil 8 is generated on both sides of the condensing lens 1 in the y-coordinate direction, and this position is located between the leaf springs 3a, 3b, 3a',
Since it is along the center axis of the torsion of the movable part 2, even if there is an imbalance between the driving forces generated at the two locations, vibrations in the torsional direction of the movable part 2 will not be excited.

According to this embodiment, the rigidity against torsional vibration of the movable part can be increased, and as a result, the resonant frequency that causes the tracking position shift of the condensing lens can be set high, and therefore a sufficient tracking servo band can be set. Therefore, it is possible to control the position of the condensing lens at high speed, and at the same time, it is possible to obtain an actuator having homogeneous characteristics.

It should be noted that this embodiment does not limit the present invention in any way, and it goes without saying that any changes may be made without departing from the spirit of the present invention.

〔Effect of the invention〕

According to the present invention, by using a movable part equipped with a condensing lens with a small moment of inertia, flanges provided at both ends and the center, and a plate spring provided with a flexible part in the middle, the movable part is twisted. It is possible to obtain a lens actuator that increases the resonance frequency of vibration and operates at high speed, and at the same time, it is possible to realize homogeneous dynamic characteristics.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing one embodiment of the present invention, FIG. 2 is a perspective view of the embodiment shown in FIG. 1, and FIG. 3 is a configuration of the embodiment shown in FIG. 1. A perspective view of the included leaf spring, FIG. 4, is a sectional view at a point in FIG. 1... Condenser lens, 2... Movable part, 3a, 3
b, 3a', 3b'...plate spring, 4...arm, 5...
... Swinging support mechanism, 6... Body, 7... Shaft, 8
... Focus coil, 9 ... Tracking coil, 10a, 10b ... Center yoke, 11
a, 11b... Magnet, 12a, 12b... Side yoke, 13a, 13b... Hole, 14, 15,
15', 16...flange.

Claims (1)

[Scope of Claims] 1. A movable part equipped with a condensing lens that condenses light from a light source onto the surface of a recording medium, an arm, and one end connected to both sides of the movable part in the tracking direction and above and below in the focus direction, respectively. , a flanged spring portion is provided at three locations at both ends and an intermediate portion thereof in parallel with a longitudinal direction perpendicular to the tracking direction and the focusing direction of the movable portion, and the flange is connected to the movable portion. a plurality of leaf springs that are movable in the focus direction and have a structure in which a flexible portion is provided between each of the flanged spring portions connected to the attached spring portion and the arm, and the intermediate flanged spring portion; a swinging support mechanism that supports the following on a body so as to be swingable around an axis parallel to the focus direction; and a focus coil that is present between the upper and lower leaf springs and is provided in the movable part. and a tracking coil, which is provided on the said body and of the said condensing lens.
A lens actuator comprising two magnetic circuits magnetically coupled to the focus coil and the tracking coil on both sides in a direction perpendicular to a tracking direction.