JPH0725859Y2 - Mirror actuator for focus position control - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to improvement of dynamic characteristics of an actuator used for a focus position control mechanism such as an optical disc pickup optical system.

<Prior Art> FIG. 4 (a) is a configuration diagram showing an example of a conventional lens actuator, and FIG. 4 (b) is a configuration diagram showing an example of focus position control using the lens actuator of FIG. 4 (a).

In FIG. 4A, the lens holder 22 holding the objective lens 21 is supported by the parallel leaf spring 23. A focus coil 24 and a magnetic circuit 25 are installed in the lens holder 22 to form a voice coil motor. By energizing the focus coil 24, the objective lens 21 is driven in the focus direction. In the focus position control using the lens actuator 2 having such a configuration, the deviation between the medium surface of the optical disc 1 and the focus position is detected by the focus error detection optical system 3 of the optical disc pickup optical system in FIG. Using this detection signal, the preamplifier 4,
Through the control circuit 5, the focus coil 24 of the lens actuator 2 is energized so that the focus position deviation becomes zero,
The objective lens 21 is driven in the focus direction with respect to the optical disc 1.

<Problems to be Solved by the Invention> However, in the focus position control using the lens actuator shown in the above-mentioned prior art, since the driving force generated by the boil coil motor configured by the focus coil 24 and the magnetic circuit 25 is small, the objective When driving the weight of the lens 21 and the lens holder 22, a sufficiently large acceleration cannot be obtained, and higher-order resonance occurs at around 10 kHz, so the bandwidth of the servo system cannot be sufficiently widened. However, there is a problem that the followability deteriorates with respect to the high-speed rotation (3600 rpm or more) of the optical disc 1.

The present invention has been made in view of the above-mentioned problems of the prior art, and provides a mirror position controlling mirror actuator having a high response frequency capable of following the focus position even at a high speed rotation (3600 rpm or more) of an optical disk. This is the purpose.

<Means for Solving the Problems> The structure of the present invention for solving the above problems is a laminated piezoelectric element having a spherical projection on one surface and fixed to the other surface of the laminated piezoelectric element. Plate, a flat mirror in which the spherical projection of the laminated piezoelectric element is in contact with the center of the back surface thereof, and the outer peripheral portion of the flat mirror is supported by the flange portion and is fixed to the plate by a fixing screw. The flat mirror, the laminated piezoelectric element, and a plate are housed in a case for adjusting the expansion / contraction displacement amount by controlling the voltage applied to the laminated piezoelectric element, and changing the curvature of the planar mirror to form a curved surface. It is characterized by being transformed into.

<Operation> According to the present invention, the lightweight flat mirror is displaced by the laminated piezoelectric element that generates a large force, and the flat mirror can be driven at high speed.

<Example> Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1A is a configuration diagram showing an embodiment of a mirror actuator for focus position control according to the present invention.

In FIG. 1A, 11 is a plane mirror, 12 is a laminated piezoelectric element, and a spherical projection is provided at the tip thereof. The spherical projection of the laminated piezoelectric element 12 is in contact with the center of the back surface of the plane mirror 11. Reference numeral 14 denotes a plate, which is fixed to one side surface of the laminated piezoelectric element 12. Reference numeral 15 denotes a case, in which the flat mirror 11, the laminated piezoelectric element 12, and the plate 14 are housed, and the outer peripheral portion of the flat mirror 11 is supported by the flange portion of the case 15. A fixing screw 16 fixes the plate 14 and the case 15 with a screw at a position where the outer peripheral portion of the flat mirror 11 and the flange portion of the case 15 come into contact with each other.

The operation of such a configuration will be described with reference to FIG. In the figure (b), when a voltage is applied to the laminated piezoelectric element 12, it extends in the direction of the arrow and is displaced. The plane mirror 11 is pushed by the spherical projection 13 of the laminated piezoelectric element 12, but since the outer peripheral portion is supported by the flange of the case 15,
Deforms into a curved surface. The curvature of this curved surface is the laminated piezoelectric element 12
It can be controlled by the voltage applied to the.

FIG. 2A is a configuration diagram showing an embodiment of focus position control using the focus position control mirror actuator of FIG. 1A. In FIG. 2 (a), the same elements as those in FIG. 4 are designated by the same reference numerals, and a duplicate description will be omitted.

In FIG. 2A, 6 is a semiconductor laser, 7 is a collimator lens, 8 and 9 are beam splitters, and 10 is a mirror actuator for focus position control of the present invention.

In such a configuration, the emitted light of the semiconductor laser 6 is
The collimator lens 7 collimates the light beam, advances straight through the beam splitter 8, bends the optical path at a right angle by the beam splitter 9, and vertically enters the plane mirror 11 of the focus position control mirror actuator 10. The light beam reflected by the plane mirror 11 advances straight through the beam splitter 9 and enters the objective lens 21 fixed in the optical system for optical disc pickup. The light flux is narrowed down by the objective lens 21 and focused on the medium surface of the optical disc 1. The reflected light from the optical disk 1 passes through the objective lens 21 and the beam splitter 9 and is reflected again by the plane mirror 11. The reflected light is sequentially reflected by the beam splitters 9 and 8, and the focus error detection optical system 3
Is converted into an electric signal by.

Here, as shown in FIG. 2B, when the position of the optical disc 1 changes, an electric signal corresponding to the error between the focal position of the objective lens 21 and the medium surface of the optical disc 1 is transmitted by the focus error detection optical system 3. Occur. This signal is sent to the preamplifier 4
Then, the control circuit 5 controls the laminated piezoelectric element 12 of the focus position control mirror actuator 10 to expand so that the error is reduced. When the plane mirror 11 of the focus position control mirror actuator 10 becomes a curved surface, the objective lens 21
The light beam incident on is changed from a parallel light beam, and the focal position of the objective lens 21 and the medium surface of the optical disc 1 are controlled to coincide with each other. Further, the reflected light from the optical disc 1 at the in-focus position becomes a parallel light flux when reflected by the plane mirror 11 of the focus position control mirror actuator 10, and enters the focus error detection optical system 3. That is, at the in-focus position, the light beams incident on the focus error detection optical system 3 are always in the same state.

As shown in FIG. 3, the thickness distribution of the flat mirror is changed according to the radius so that the curved surface shape when the flat mirror is displaced by expansion and contraction of the laminated piezoelectric element becomes spherical.
It is also possible to adopt a configuration in which the wavefront aberration does not increase.
It is also possible to set the thickness distribution of the plane mirror so that not only the spherical surface but also an arbitrary aspherical shape can be obtained.

<Effects of the Invention> As described in detail above with reference to the embodiments, in the mirror actuator for focus position control of the present invention, the plane mirror is extremely lightweight and the generated force of the laminated piezoelectric element is large. Can be driven at high speed. Therefore, the response frequency can easily be set to 10 kHz or higher. Further, the focus position control using the focus position control mirror actuator of the present invention can obtain a servo band band which can sufficiently follow the shake in the focus direction when the optical disk rotates at a high speed. Furthermore,
Since the objective lens is fixed, unlike the conventional lens actuator, the objective lens does not hit the optical disc and damage the optical disc or the objective lens when the focus servo is deviated, so that the reliability can be improved. It is possible to realize a mirror actuator for focus position control having advantages such as the above.

[Brief description of drawings]

FIG. 1 (a) is a configuration diagram showing an embodiment of a focus position control mirror actuator according to the present invention, and FIG. 1 (b) is a configuration for explaining the operation of the focus position control mirror actuator of FIG. Fig. 2 (a) is Fig. 1 (a).
Of the focal position control using the mirror actuator for controlling the focal position of FIG. 3, (b) is a structural view for explaining the operation, and FIG. 3 is another embodiment of the plane mirror. A side view, FIG. 4 (a) is a configuration diagram showing an example of a conventional lens actuator, and FIG. 4 (b) is a configuration diagram showing an example of conventional focus position control using the lens actuator of FIG. 4 (a). 10 …… Mirror actuator for focus position control, 11 …… Planar mirror, 12 …… Multilayer piezoelectric element, 13 …… Spherical protrusion, 14 …… Plate, 15 …… Case, 16 …… Fixing screw.

Claims (1)

[Scope of utility model registration request] 1. A laminated piezoelectric element having a spherical protrusion on one surface, a plate fixed to the other surface of the laminated piezoelectric element, and a spherical protrusion of the laminated piezoelectric element. A case for accommodating the flat mirror, the laminated piezoelectric element, and the plate, the flat mirror being in contact with the central portion of the back surface, the outer peripheral portion of the flat mirror being supported by its flange, and the plate being fixed by a fixing screw. Consists of,
A focal position control mirror actuator, wherein the expansion / contraction displacement amount is adjusted by controlling the voltage applied to the laminated piezoelectric element to change the curvature of the plane mirror to deform it into a curved surface.