JPH0192933A - Lens actuator - Google Patents

Abstract

PURPOSE:To attain high speed operation by using a moving part mounted with a condenser lens with a small moment of inertia thereupon and a plate spring in the middle of which a flange is provided so as to increase the resonance frequency of the torsional vibration of the moving part. CONSTITUTION:A flange is provided in the middle part of plate springs 3a, 3b, 3a', 3b' supporting movably the moving part 2 in the focus direction so as to reduce the moment of inertia of the moving part in the focus direction, tracking direction and lengthwise direction orthogonal to the former two directions deciding the resonance frequency of the torsional vibration of the moving part 2 and also to increase the stiffness of the plate springs 3a, 3b or the like supporting the moving part. Then the moving part 2 is not prolonged in the focus direction and the moment of inertia around the lengthwise direction is made small. High stiffness is provided to the plural plate springs 3a, 3b or the like placed between the moving part 2 and the arm except around the part bonded to the moving part 2 and the arm by using the flange given to the conventional plate spring. Thus, the lens actuator with a high torsional resonance frequency is formed to realize the high speed operation in the tracking direction.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to recording information on the surface of a recording medium using optical means, or reproducing or erasing information already recorded on the surface of the recording medium. Regarding the lens actuator of the optical head, especially when the condenser lens is
The present invention also relates to a lens actuator that moves in parallel.

[Conventional technology]

Conventionally, optical technology uses laser light as a light source and modulates this 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 always on the focal plane of the condenser lens. At the same time, the condenser lens is placed in a guide groove 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 .

Various configurations have been proposed for this type of lens actuator, one of which is a focuser.

Some devices provide movable support in the tracking direction using parallel plate springs, and provide movable support in the tracking direction using a swing support mechanism. 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 condenser lens is attached to the arm via two leaf springs that are parallel to each other in a direction perpendicular to the focus direction. Furthermore, the arm is held in the housing by a swinging support mechanism so as to be swingable in the trafking direction. Further, in order to drive the movable part in the focus direction and the tracking direction, a focus coil and a tracking coil are provided in the movable part. The focusing coil is wound below the parallel leaf springs and around the optical axis of the condensing lens mounted on the movable part, and the tracking coil is wound around the center of gravity of the movable part between the parallel leaf springs. is set to the position where it is driven.

[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, the torsion direction of the movable part, that is, the rotation direction about the longitudinal axis that is perpendicular to the tracking direction and the focusing direction, is Vibration is unavoidable. Vibration in this direction results in the optical spot caused by the condenser lens being vibrated in the tracking direction, and since the vibration in this direction is a rotational movement that cannot be controlled by the actuator in the tracking direction, the movement of the condenser 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.

An object of the present invention is to provide a lens actuator that eliminates such drawbacks, increases the resonance frequency of torsional vibration of a movable part including a condensing lens, and realizes high-speed operation.

[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, one end of which is connected to both sides of the movable part in the tracking direction and the top and bottom of the focus direction; A flange is provided in an intermediate portion sandwiched between the provided flexible portions in parallel with a longitudinal direction that is orthogonal to the tracking direction and the focus direction of the movable portion, and a plurality of leaf springs movable in the focus direction. , an arm to which the other ends of the plurality of leaf springs are connected; a swing support mechanism that supports the arm in a housing so as to be swingable around one axis parallel to the focusing direction; A focus coil and a tracking coil that are present between the leaf springs and are provided on the movable part, and a focus coil and a tracking coil that are provided on the housing and on both sides of the condensing lens in a direction perpendicular to the tracking direction. and two magnetic circuits that are magnetically coupled to each other.

[Effect]

In order to set the resonance frequency of the torsional direction vibration of the movable part high, the lens actuator of the present invention provides a flange in the middle part of the temporary spring that supports the movement of the movable part in the focus direction. The focus direction and tracking of the movable part determine the frequency of vibration resonance,
The structure reduces the moment of inertia of the movable part in the longitudinal direction that is orthogonal to the moving direction, and at the same time increases the rigidity of the leaf spring that supports the movable part. According to such a configuration, 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 made highly rigid by flanges provided on ordinary temporary springs, except for the vicinity where they are joined to the movable part and the arm. The synergistic effect of the above two effects makes it possible to create a lens actuator that is lightweight and highly rigid, and has a high torsional resonance frequency, and can realize high-speed operation in the tracking direction.

〔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 2nd coordinate direction indicates the focus direction.

The lens actuator of this embodiment includes a condenser lens 1,
Focus coil 8, tracking coil 9, movable part 2, plate springs 3a, 3a', 3b, 3b', arm 4, swing support mechanism 5, center yoke 10a, 10
b, and two magnetic circuits consisting of magnets 11a and llb provided on the housing 6 and side yokes 12a 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.

The movable part 2 has two holes 13a 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).

13b is opened. These two holes 13a, 13
A focusing coil 8 is wound in parallel to the xy plane so as to surround the lens 1 and the condenser lens 1. Furthermore, four tracking coils 9 are bonded onto 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. .

The leaf springs 3a, 3a', 3b, 3b' support the movable part 2 with respect to the arm 4, and in this embodiment, the condenser lens 1
The lower surfaces of one end of the leaf springs 3a and 3b are respectively joined to the upper surfaces of the upper protruding parts at both ends in the tracking direction (X coordinate direction) of the movable part 2 on which the movable part 2 is mounted. , leaf springs 3a', 3b
′ is attached to the top surface of each end. These four leaf springs are installed parallel to the y-coordinate direction. Leaf spring 3a
The lower surface of the other end of the leaf spring 3b and the lower surface of the other end of the leaf spring 3b are attached to the upper surface of the arm 4, forming the leaf spring 3a'.

The upper surface of each other end of 3b' is attached to the lower surface of the arm 4. At this time, the leaf springs 3a and 3a/, and the leaf springs 3b and 3b' are set to be parallel to each other. The movable portion 2 is movably supported in the focus direction (two coordinate directions) by these four leaf springs.

The structure of these leaf springs will be explained in detail using 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 W shown in FIG. p, q, r in Figure 3,
s, t, and u each indicate the position in the longitudinal direction of the leaf spring. In the range from position p to r and from position S to U, the leaf spring has a simple flat plate structure and can be easily bent in the focus direction, and in the range from position p to ql and from t to U, the leaf spring has a simple flat plate structure, and in the range from position p to ql and from t to U, respectively. It is joined to the movable part 2 and arm 4 shown in FIG. On the other hand, between position r and S, there are flanges 14 on both sides parallel to the longitudinal direction of the flat spring.
14' is formed, and as a result, the cross-sectional shape cut at the cross-section W becomes a U-shape as shown in FIG. Therefore, in this structure, the spring has low bending rigidity from position q to r and from position S to t, and high bending rigidity from position r to S, and the spring has high bending rigidity from position r to S. The bending displacement of the flat spring can be used to cope with the bending displacement, and the effect of the flange in the center can provide a structure with high rigidity against torsional displacement.

The swing support mechanism 5 is a mechanism that can swing around an axis 7 parallel to the focus direction (two-coordinate direction). The swing support mechanism 5 includes four leaf springs 3a.

The surface of the arm 4 on the opposite side of the arm 4 surrounded by 3b, 3a', 3b' is attached, and the arm 4 is fixed to the swing support mechanism 5. The swing support mechanism 5 includes an arm 4
For body 6, pho.

- It is swingably supported with an axis 7 parallel to the scrap direction (two-coordinate direction) as the center/Cψ. Therefore, the movable part 2 is movably supported also in the tracking direction (X coordinate direction).

The magnetic circuit includes center yokes 10a and 10b.
It is composed of one stone 11a, llb and side yokes 12a, 12b, and is installed on the housing 6. The center yokes 10a and 10b are located in the holes 13a and 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 X-coordinate direction by the magnet in the gap of the magnetic circuit, and as a result, the movable part 2 is driven in the focus direction (two-coordinate direction) by applying current to the focus coil 8, and the tracking coil 9 By applying a current to the condenser lens 1, the condenser lens 1 is driven in the tracking direction (X coordinate direction), and the condenser lens 1 is moved in the focusing direction and 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 do.

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 made stiff in the middle by providing a flange on the temporary spring, so that the entire leaf spring is soft in the focusing direction and torsional. It can be rigid in the direction. Due to these synergistic effects, the movable part 2
The torsional vibration resonance frequency of can be set high.

In addition, support for movement of the condensing lens in the tracking direction is
Since this is carried out by rotational support, there is no need for the arm 4 to perform the same movements 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 condenser lens 1 in the X-coordinate direction, and these positions correspond to the leaf springs 3a, 3b, and 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 places, vibrations in the torsional direction of the movable part 2 will not be excited.

FIG. 5 is a perspective view showing another embodiment of the present invention. Regarding the configuration of the lens actuator of this example,
Although it is almost the same as the lens actuator shown in FIG. 1, the shape of the leaf springs corresponding to the four leaf springs shown in FIG. 1 is different. In addition, in FIG. 5, leaf spring 2
3a, 23a'.

23b is shown. In this way, in the lens actuator shown in FIG. 1, the shape of the leaf spring is made to have a constant width in the tracking direction, whereas in this embodiment,
The shape of the leaf spring is narrower at the joint with the movable part 2, and the shape of the leaf spring is narrower at the joint with the movable part 2.
The lens actuator is tapered to become wider at the joint with the lens actuator, and its function and effect are similar to those of the lens actuator shown in FIG.

The above two embodiments have been described. According to these embodiments, the rigidity against torsional vibration of the movable part can be increased, and as a result, the resonant frequency that causes the track position shift of the condensing lens can be set high. Therefore, since a sufficient tracking servo band can be secured, the condenser lens position can be controlled at high speed.

〔Effect of the invention〕

As explained above, according to the present invention, by using a movable part equipped with a condensing lens with a small moment of inertia and a leaf spring provided with a flange in the center, the resonant frequency of torsional vibration of the movable part is increased. A lens actuator that operates at high speed can be obtained.

[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 one embodiment, FIG. 3 is a perspective view of a leaf spring included in the configuration of one embodiment, and FIG. The figure is a cross-sectional view of the leaf spring shown in FIG. 3, and FIG. 5 is a perspective view showing another embodiment of the present invention. l...Condensing lens 2...Movable parts 3a, 3b, 3a', 3b'---Plate spring 4...
Arm 5... Swing support mechanism 6... Body 7... Axis 8... Focus coil 9... Tracking coils 10a, 10b... Center yoke 11a, llb - Magnet 12a, 12b... Side yoke 13a, 13b... Hole 14.14'... Flange agent Patent attorney Yoshiyuki Iwasa Figure 1 Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] (1) A movable part equipped with a condensing lens that condenses light from a light source onto the surface of a recording medium; A plurality of leaf springs movable in the focus direction are provided with flanges parallel to the longitudinal direction, which are perpendicular to the tracking direction and the focus direction of the movable part, in the intermediate part sandwiched between the radial parts; and the plurality of leaf springs. an arm to which the other end of the leaf spring is connected; a swing support mechanism that supports the arm in a housing so as to be swingable around an axis parallel to the focusing direction; a focus coil and a tracking coil that are present and provided in the movable part; and a focus coil and a tracking coil that are provided in the housing and are magnetically connected to the focus coil and tracking coil on both sides of the condensing lens in a direction perpendicular to the tracking direction. A lens actuator having two coupled magnetic circuits.