JPS63103207A - Focus position controller for lens - Google Patents

Abstract

PURPOSE:To simplify the structure of a focus position controller and to follow up a focus position even when the focus position is controlled at a high frequency by varying and controlling a voltage impressed between both surfaces of a lens of piezoelectric ceramics and controlling the focus position of the lens. CONSTITUTION:This film discoid electrodes 12 and 13 made of conductive materials with good light transmissivity are fixed on the top and reverse surfaces of a lens which is formed of the piezoelectric ceramics with good light transmissivity in a convex lens shape. When an optical disk rotates and is displaced owing to the curvature or irregularity of its signal surface, a displacement detecting circuit detects the quantity of the displacement. A control voltage output circuit 14 outputs a corresponding control voltage according to the displacement detection signal and impresses it between the electrodes 12 and 13; when the optical disk 3 is displaced to a position shown by a dotted line, the lens 11 is strained in such a direction that the focal length become short. Consequently, the signal surface of the optical disk 3 is irradiated with a laser light beam 8 in a fine spot and the focus position 9 moves to a position shown by a dotted line. Consequently, the position is traced and controlled even at the high frequency of a driving circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is used for focusing servo, tracking servo, etc. in the optical pickup of an optical disk device. The present invention relates to a lens focal position control device that variably controls the focal position of a lens in response to changes in the focal position of the lens.

[Prior Art] Conventionally, a focal position control device for this type of lens has been constructed as shown in FIG. In this figure, (1) is a lens formed into a predetermined shape using an optical glass material, and (2) is a lens (
1), an actuator coil integrally attached to (3)
) is an optical disk, (4) (4) is a magnet, (5) (5)
is a magnetic circuit. (6) (6) (6) (6) is a spring that supports the lens (1) and the actuator coil (2) in a predetermined position in a state where they can be moved downward.

When the optical disk (3) rotates and is displaced to the position indicated by a dotted line or a dashed-dotted line due to warping or unevenness of its signal surface, an output from the drive circuit (7) is based on a detection signal output from a circuit that detects this displacement. A corresponding control current flows through the actuator coil (2), and the lens (1)
was driven to the position shown by the dotted line or the dashed line, and the focal position (9) where a minute spot of the laser beam (8) was formed was controlled on the signal surface of the optical disc (3).

[Problems to be Solved by the Invention] As mentioned above, in the conventional example shown in FIG. 3, the focal position (9) was controlled by mechanically driving the lens (1), so the actuator coil (2),
Drive mechanisms such as magnets (4) (4), magnetic circuits (5) (5), and springs (6) (6) (6) (6) are required, making the structure complex and requiring adjustments between individual mechanisms. The problem was that it was complicated. In addition, the drive circuit (7
) becomes higher, there is a problem in that it becomes difficult to make the mechanical drive of the lens (1) follow this frequency.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a lens focal position control device that has a simple structure and can follow and control even high frequencies.

[Means for Solving the Problems] A lens focal position control device according to the present invention has a lens formed of piezoelectric ceramics with good translucency, and a thin film made of a conductive material with good translucency on both sides of the lens. The lens is characterized in that shaped electrodes are fixed and the focal position of the lens is controlled by variably controlling the voltage applied between the electrodes.

[Operation] When a voltage is applied via electrodes to both sides of a lens made of piezoelectric ceramics with good translucency, the lens deforms (distorts) in response to the applied voltage due to the inverse piezoelectric effect of the piezoelectric ceramics. ). For example, when a voltage (electric field) is applied from the front side to the back side of a piezoelectric ceramic formed in the shape of a convex lens, the focal length becomes shorter due to the inverse piezoelectric effect of the piezoelectric ceramic (the focal position approaches the lens). When a voltage (electric field) is applied from the back side to the front side, the lens deforms in the direction in which the focal length becomes longer (the focal point moves away from the lens). Therefore, the focal position of the lens can be controlled simply by variably controlling the voltage applied to both surfaces of the lens via the electrodes.

Furthermore, since the control is such that the lens is directly deformed by the applied voltage, even if the frequency of the applied voltage becomes high, the focal position of the lens can be made to follow this.

[Example] Figures 1 and 2 show an example of the present invention.
In these figures, (11) is a lens formed into a convex lens shape using piezoelectric ceramics with good translucency.

The lens (11) is made of, for example, PZT (zircon titanium), which is a solid solution of lead zirconate (P b Z r O3) and lead titanate (P b TiOa ) in an appropriate ratio, although it is not limited thereto. acid lead) and lanthanum (La
) is added and hot pressed to form an electro-optic ceramic with good translucency, PL ZT.

Thin film disk-shaped electrodes (12) and (13) made of a conductive material with good translucency are fixed to the front surface (upper surface) and back surface (lower surface) of the lens (11), respectively. (3)
is an optical disc such as a CD (compact disc). (14) detects the amount of displacement of the optical disc (3) between the electrodes (12) and (13) based on a detection signal from a detection circuit (for example, a focusing error detection circuit) that detects the displacement of the optical disc (3). This is a control voltage output circuit that applies a corresponding control voltage for displacing the focal position (9) of the lens (1).

Next, the operation of the above embodiment will be explained.

(a) When the optical disc (3) is rotating at the position shown by the solid line with no displacement, there is no detection signal output from the displacement detection circuit (for example, the focusing error detection circuit) (not shown), so the control voltage output circuit (14 The control voltage output from ) is zero. Therefore, the lens (11) is not deformed, and the laser beam (8) is refracted as shown by the solid line to irradiate a minute spot on the signal surface of the optical disc (3), and the focal position (
9) is the position of the solid line.

(b) When the optical disk (3) rotates and is displaced to a position indicated by a dotted line or a dashed-dotted line due to warping or unevenness of its signal surface, the amount of displacement is detected by a displacement detection circuit (not shown). Based on this displacement detection signal, a corresponding control voltage is output from the control voltage output circuit (14), and the electrode (1
2) Apply between (13). In other words, an optical disc (
3) is displaced to the position shown by the dotted line, the electrode (1z) on the front side (top side) of the lens (11) is positive, and the electrode (1z) on the back side (
The electrode (13) on the lower surface side is negative and outputs a control voltage corresponding to the amount of displacement, and the lens (11)
) as shown by the dotted line (i.e. the lens (11
) is distorted in the direction of shortening the focal length). Therefore, the laser beam (8) is refracted as shown by the dotted line and irradiates a minute spot on the signal surface of the optical disc (3) displaced to the position shown by the dotted line, and the focal position (9) becomes the position shown by the dotted line. Furthermore, when the optical disc (3) is displaced to the position shown by the dashed line, the control voltage output circuit (4) indicates that the electrode (13) on the back side of the lens (11) is positive and the electrode (12) on the front side is positive. A control voltage that is negative and has a magnitude corresponding to the amount of displacement is output, and the lens (11) is deformed as shown by the dashed line (that is, the lens (11) is distorted in the direction of increasing the focal length). Therefore, the laser beam (8) is refracted as shown by the dashed-dotted line, and irradiates a minute spot on the signal surface of the optical disc (3) displaced to the position indicated by the dashed-dotted line, and the focal position (
9) is at the position indicated by the dashed-dotted line.

In the above embodiment, the focus position control of the lens used for the focusing servo in the optical pickup of an optical disk device was explained. However, the present invention is not limited to this, and can be generally used for controlling the focus position of the lens. can.

In the above embodiment, the focal position of a single convex lens is controlled, but the present invention is not limited to this, and can also be applied to cases where the focal position of a single concave lens, a combination of convex lenses, a combination of concave lenses, etc. is controlled. Available.

[Effects of the Invention] As described above, the lens focal position control device according to the present invention includes a lens formed of piezoelectric ceramics with good translucency,
The focal position of the lens is controlled simply by variable control of the voltage applied to both sides of the lens, compared to conventional examples in which the focal position is controlled by mechanically driving the lens itself. , the structure becomes extremely simple, and the focal position of the lens can also be controlled at a high frequency.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a lens focal position control bag holder according to the present invention, FIG. 2 is a plan view of the main part of FIG. 1, and FIG. 3 is a block diagram showing a conventional example. (3)...Optical disc, (9)...Focus position, (1
1)...Lens, (12) (13)...Electrode, (
14)... Control voltage output circuit. Applicant: Fujitsu General Ltd. Figure 1 Figure 2 Figure □ 9JE3

Claims (2)

[Claims] (1) A lens is formed from piezoelectric ceramics with good light transmittance, thin film-shaped electrodes made of a conductive material with good light transmittance are fixed to both sides of the lens, and the voltage applied between the electrodes is variably controlled. 1. A lens focal position control device, characterized in that the focal position of the lens is controlled by: (2) The focal position control device for a lens according to claim 1, wherein the piezoelectric ceramic having good translucency forming the lens is made of PLZT.