JPH01112532A - Lens actuator - Google Patents

Abstract

PURPOSE:To obtain a lens actuator for high speed operation by using a moving part mounting a condenser lens with a small moment of inertia and a plate spring with a flange at both ends and in the center and with a flexible part inbetween. CONSTITUTION:A focus coil 8 is placed between upper and lower plate springs, then the moving part 2 is decreased in the focus direction thereby reducing the moment of inertia of the moving part 2 mounting the condenser lens 1 with respect to the torsional direction of the plate spring as a result. Moreover, the stiffness around the part of the plate spring bonded with the moving part 2 and an arm 4 is made flexible and the intermediate part is made stiff by providing a plate spring to the plate spring in the distribution of the stiffness of the plate spring thereby making the plate spring flexible in the focus direction and stiff in the torsional direction. Then the torsional vibration resonance frequency of the moving part 2 is set higher by the synergistic effect of them. Furthermore, the flange is provided to the end of the bonded part between the moving part 2 and the arm 4 of the plate spring to attain high stiffness, and an elasticity is provided to the flexible part clipped between the high stiffness part and the part with the flange inbetween so as to make the elastic characteristic of the flexible part uniform thereby forming homogeneous vibration characteristic.

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 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 one in which movable support in the focus direction is performed by a parallel leaf spring, and movable support in the tracking direction is performed by a swing support mechanism. . For example, patent application 1983-
The lens actuator proposed in the specification of No. 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. Further, the arm is held in the housing by a swing support mechanism so as to be swingable in the tracking 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. 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 actuators must be adjusted, but there are also disadvantages in that characteristics vary 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 condenser lens, realize high-speed operation, and create a lens with the characteristic small dynamic characteristic of solid lid opening. Our goal is to provide actuators.

[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 connected to each side of the movable part in the tracking direction and above and below in the focusing direction. , 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 a flange is connected to the movable portion. a plurality of leaf springs movable in a focusing direction, each of which has a structure in which a flexible portion is provided between a flanged spring portion connected to the attached spring portion and the arm, and an intermediate flanged spring portion, and the arm; a swinging support mechanism that supports the following in a housing so as to be swingable around one axis parallel to the focusing direction; and a focusing coil and tracking that are located between the upper and lower leaf springs and are provided in the movable part. A coil; and two magnetic circuits provided in the housing and magnetically coupled to the focus coil and the tracking coil on both sides of the condenser lens 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 torsional vibration of the movable part, and at the same time uses a leaf spring to support the movable part. By adopting a structure with increased rigidity, 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 multiple temporary springs installed between the movable part and the arm are attached to the leaf spring, except for the flange attachment near the movable part and the arm and the intermediate part, which are sandwiched between the parts. High rigidity is achieved by the flange. 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. In addition, by setting the leaf spring as in the configuration of the present invention, the length of the flexible part, which has the greatest effect on the dynamic characteristics of the movable part, and the boundary conditions with the flanged spring part can be kept constant due to the integral height. 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, FIG. 1 is an exploded perspective view, and FIG. 2 is a perspective view. For convenience of explanation, the parts in FIG. Set an orthogonal Cartesian coordinate system to . 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, leaf springs 3a, 3a', 3b, 3b', arm 4, rotation support mechanism 5, center yoke 10a, 10
b, and two magnetic circuits consisting of magnets 11a and llb provided on the wall body 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 l.

The movable part 2 has two holes 13a at positions on both sides of the condenser lens 1 in the focus direction (X 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 b and the condenser lens l. 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 X coordinate direction of the holes 13a and 13b. .

Leaf spring 3 a+ 38' + 3 b+ 3
b' supports the movable part 2 with respect to the arm 4, and in this embodiment, the upper surface and side surface of the upper protrusion at both ends in the tracking direction (X coordinate direction) of the movable part 2 on which the condenser lens 1 is mounted. The lower surface of one end of the leaf springs 3a, 3b and the inner surface of the flange portion are respectively joined, and the leaf spring 3a is attached to the lower surface and side surface of the lower protrusion at both ends of the movable part 2 in the tracking direction.
The upper surface of one end portion and the inner surface of the flange portion of ', 3b' are attached, respectively. These four leaf springs 3a+ 3bl
3a'l 3b' are installed parallel to the X coordinate direction.

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

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 X shown in FIG.

p+ qr r, S+ L+ u, V in Figure 3
, W indicate the position in the longitudinal direction (X coordinate direction) of the leaf spring, respectively. The temporary spring has a simple flat plate structure in the ranges from position r to S and from position t to U, and can be easily bent in the focus direction (two coordinate directions), and from position p to q and from V to W. The leaf springs 3a each have the first
The movable part 2 shown in the figure is joined to the arm 4 including flanges 14 and 16.

On the other hand, between position S and t, flanges 15 and 15' are formed on both sides parallel to the longitudinal direction of the flat spring, and as a result, the cross-sectional shape cut at cross-section X is as shown in FIG. It becomes a U-shape. Therefore, in this structure, the bending rigidity is small from position r to S and from position t to U.
From positions Wq to r, from s to t, and from u to V, the springs have high bending rigidity, and the displacement of the movable part 2 in the focus direction is handled by the bending displacement of the flat spring from position r to position S1 to U. , and the effect of the flanges 15, 15' at the center allows a structure with high rigidity against torsional displacement. At the same time, by using the leaf spring of this example,
Compared to the conventional structure in which the movable part and the arm part are connected using a simple leaf spring, the size of the flexible part that undergoes deformation when the movable part bends in the focus direction can maintain the design 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 and effective joint length will vary depending on the product, resulting in changes in the dynamic characteristics of the movable part. This can be avoided in this embodiment because the flexible part strictly realizes the design value, and the spring can have uniform dynamic characteristics.

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 r3b, 3a',
The face of the arm 4 on the opposite side of the arm 4 surrounded by 3b' is attached, and the arm 4 is fixed to the swing support mechanism. The swing support mechanism 5 supports the arm 4 to be swingable about an axis 7 parallel to the focus direction (two-coordinate direction) with respect to the housing 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 and a magnet 11.
a, llb and side yokes 12a, 12b, and is installed on the housing 6. center yoke 10
a 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 in the middle, a flange is provided on the temporary spring to make it stiff, so that it is soft in the focusing direction and stiff in the torsional direction. It can be done. Due to these synergistic effects, the resonant frequency of the torsional vibration of the movable part 2 can be set high. Also, the movable part 2 of the leaf spring
The joint part with the arm 4 is provided with a flange at the end to make it highly rigid, and the flexible part sandwiched between these high-rigidity parts and the intermediate flanged part has a structure with spring properties, thereby making it flexible. The size of the flexible portion can be set precisely, so that the spring characteristics of the flexible portion can be uniform, and the vibration characteristics can be made homogeneous.

In addition, since the movement of the condensing lens 1 in the tracking direction is supported by swinging support, there is no need for the arm 4 to perform the same movement as the movable part 2, and there is no need to cause the leaf spring to cause torsional vibration. It has a structure that does not require any force.

The driving force of the focus coil 8 is generated on both sides of the condensing lens l in the y-coordinate direction, and this position is the position of the leaf springs 3 a r 3 b , 3 a ' r
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.

According to this embodiment, the rigidity against torsional vibration of the movable part can be increased, and as a result, the resonance frequency that causes the track position shift of the condenser lens can be set high.
Therefore, since a sufficient tracking servo band can be secured, 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.

Note that this example does not limit the present invention in any way,
It goes without saying that any changes may be made without departing from the spirit of the invention.

〔Effect of the invention〕

According to the present invention, a movable part equipped with a condensing lens having a small moment of inertia, and flanges provided at both ends and the center,
By using a temporary spring with a flexible part provided in the middle, it is possible to increase the resonance frequency of the torsional vibration of the movable part and obtain a lens actuator that 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.
FIG. 4 is a perspective view of a leaf spring included in the configuration of the embodiment shown in the figure. FIG. 4 is a sectional view at a point in FIG. 3. 1... Condensing lens 2... Movable parts 3a, 3b, 3a', 3b'... Leaf spring 4...
・Arm 5... Swing support mechanism 6... Body 7... Axis 8... Focus coil 9... Tracking coil IOA, 10b... Center Yoke 11a, l
lb --- Magnet 12a, 12b... Side yoke 13a, 13b... Hole 14, 15.15', 16... Flange agent Patent attorney Yoshiyuki Iwasa Figure 1 Figure 3 Figure 3a Figure 4 figure

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, an arm, and one end connected to both sides of the movable part in the tracking direction and above and below in the focusing direction, and A flanged spring part is provided at three locations in the middle part, and the flanged spring part is provided with flanges parallel to the longitudinal direction perpendicular to the tracking direction and the focusing direction of the movable part, and the flanged spring part is joined to the movable part. A plurality of leaf springs movable in the focus direction are provided with flexible parts between the flanged spring part connected to the arm and the intermediate flanged spring part, and the arm is moved in the focus direction. a swing support mechanism that is supported in the housing so as to be swingable around an axis parallel to the above; a focus coil and a tracking coil that are present between the upper and lower leaf springs and are provided in the movable part; A lens actuator comprising two magnetic circuits provided in a housing and magnetically coupled to the focus coil and the tracking coil on both sides of the condenser lens in a direction perpendicular to the tracking direction.