JPS63217536A - Objective lens driver - Google Patents

Abstract

PURPOSE:To improve the sensitivity of the drive by providing a prevention means to prevent the leak of magnetic flux from the open part of magnetic circuit. CONSTITUTION:The titled driver is covered with a cover 10 to protect moving parts from an external impact, and on the inner surface of the cover 10, iron pieces 11 excellent in permeability are bonded in locations where magnetic flux is apt to leak in a manner that they 11 are located on a magnet 6a, a yoke 5c, a magnet 6b, and a yoke 5c contacting them respectively, so that the magnetic flux leaking from a magnetic gap passes through the iron peices 11 when the objective lens driver is covered with the cover 10. With such a constitution, only by covering the titled driver with the cover 10, the magnetic circuit is held in a closed-status, and the leakage of magnetic flux from the magnetic gap can be decreased.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an objective lens provided in a device that condenses light onto an information storage medium and optically reads information in an optical disk device or the like. The present invention relates to a drive device.

(Prior Art) In general, in this type of optical disk device, in order to accurately read information from an information storage medium, it is necessary to use an objective that focuses light on the information storage medium against warping or wobbling of the storage medium. It is necessary to perform focus control to control the distance between the lens and the track position of the information storage medium on which information is written, and tracking control to control the objective lens to follow the eccentricity of the information track. must be held movably in the focus direction and tracking direction.

Therefore, in the conventional objective lens drive device, as shown in Fig. 5, a focus direction drive coil (2) is wound around a holder (2) that holds the objective lens (2), and two drive coils (2) are wound on both sides of the holder (2). A pair of tracking direction drive coils (to) are bonded and connected in an integral manner.

A yoke (5a) made of a magnetic material (for example, Fe) is mounted on the base (2) as an excitation means for the drive coil (3) in the focus direction and the tracking direction.
(5b) and (5c) are installed in one body,
A pair of magnets (6a) and (6b) are attached to the inner wall surfaces of the above (5a) and (5b), respectively, facing each other, while an objective object supported by a wire (2) is attached to the outer periphery of the yoke (5c). The holder ■ of the lens ■ is inserted, and this holder ■
A magnetic circuit is constructed by winding a driving coil 0 in the focusing direction and a driving coil 2 in the tracking direction.

Then, by passing current through the drive coil (2) in the focus direction and the drive coil (A) in the tracking direction, the movable part is driven in the focus direction and tracking direction by the magnetic field of the magnetic circuit, thereby controlling the movement position of the objective lens. It is supposed to be done.

However, the effective magnetic flux (
There is a large amount of so-called leakage magnetic flux (β) that leaks relative to α), which reduces the magnetic flux density in the magnetic gap and lowers drive sensitivity.Furthermore, the magnetic flux distribution becomes non-uniform, so the magnetic flux (β) leaks due to the tilt of the objective lens. This had the disadvantage that vibrations were likely to occur.

(Problems to be Solved by the Invention) As described above, in the present invention, since there is a large amount of leakage magnetic flux from the magnets arranged opposite to each other, the magnetic flux density decreases and the drive sensitivity and
In other words, this was done to solve the problem that the amount of displacement of the movable part that moves is reduced by passing current through the focus coil and track coil, and that tilt vibration of the objective lens tends to occur due to uneven magnetic flux distribution. An object of the present invention is to provide an objective lens drive device that can increase drive sensitivity and prevent tilt vibration of an objective lens by reducing leakage magnetic flux in a magnetic gap with a relatively simple configuration.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a lens for condensing light onto an information recording medium having a recording track, and a focus direction for driving this objective lens in the focus direction. An objective lens drive device comprising: a drive coil; a track direction drive coil that is driven in a direction substantially perpendicular to the recording track direction; and a magnet that is arranged to face each of the drive coils and forms a magnetic circuit. The magnetic circuit is constructed by providing a prevention means for preventing leakage of magnetic flux from the open portion of the magnetic circuit.

(Function) That is, with the above configuration of the present invention, the magnetic gap of the magnetic circuit is closed by a magnetic conductive material (for example, an iron piece) as a leakage prevention means, so that leakage magnetic flux in the magnetic gap can be reduced. .

That is, by preventing a decrease in magnetic flux density, drive sensitivity can be increased and tilt vibration of the objective lens can be prevented.

(Example) The present invention will be described below based on an example shown in FIGS. 1 to 4. First, an overview of this device used in an optical disk device will be explained. Now, write the information,
or for reproduction purposes.

By focusing the laser beam on the surface of the information storage medium, the imaged point is guided to a predetermined position by a spiral groove carved on the information storage medium. Therefore, writing is performed by melting a thin film on the surface of the storage medium using the heat of laser light to form bits, and reading is performed by irradiating the storage medium with laser light and detecting the reflected light to determine the presence or absence of bits. It is done by recognizing.

To guide the above laser beam to a predetermined position, an optical system detects defocus and track misalignment, and a servo circuit drives an actuator to eliminate blur in the focus direction and track misalignment. need to be controlled. In order to realize this control, the moving position of the objective lens is such that the objective lens can be driven in two directions approximately perpendicular to the focus and track.

That is, as shown in Fig. 1, there is an objective lens ■, a holder ■ that holds this objective lens ■, a drive coil (3) in the focus direction (hereinafter referred to as the focus coil), and a drive coil (A) in the tracking direction (hereinafter referred to as the focus coil). , track coil) form an integral movable part and are supported by wires (2) arranged in parallel.

The above wire ■ has one end attached to the PC board (
8), and the movable part is such that the other end of the wire (2) is fitted into and supported by the holder (2). In this 1,
A vibration damping silicone rubber (a) is molded on the outer periphery of a part of the wire (2).

Furthermore, as shown in FIG.
.

(5c) is erected in one body, and the yoke (5a
).

Each inner wall surface of (5b) has a pair of magnets (6a)
.

(6b) are mounted facing each other, while the focus coil (2) and the track coil (2) are wound around the outer periphery of the yoke (5C) to form a magnetic circuit. Therefore, when a current I flows through the focus coil (■) and the track coil (A), the magnetic field shown by the arrow B in FIGS. 2 and 3 causes a force in the direction of the arrow F according to Fleming's left-hand rule, as shown by the dashed line. Occurs in position.

Therefore, the movable part exhibits a phenomenon in which the four wires (2) are bent and moved in the direction shown by arrow F due to the force of the focus coil (2) acting in the focusing direction and the force (2) of the track coil acting in the tracking direction. present. At this time, the movement of the movable part is controlled by the silicone rubber (a).
When this vibration system resonates, the vibration is damped.

In addition, the pattern of the PC board (c) has lead wires (3L) led out from both ends of the focus coil (3) and leads ffl (4L) led out from both ends of the track coil (2) shown in FIGS. 2 and 3, respectively. They are soldered, and lead wires (not shown) are soldered to each via the patterned copper foil to electrically connect them. However, when a current is supplied to the focus coil (2) or the track coil (A), the magnet (6a
) and (6b), the objective lens and the holder (2) can be moved integrally in the focus direction or the track direction.

Next, the gist of the present invention will be explained based on FIGS. 1 to 4. Conventionally, as shown in Figure 5, the effective magnetic flux (α) of the conventional gap is wide compared to the cross-sectional area, so there is a lot of leakage magnetic flux (β) from the magnetic gap, and as a result, the magnetic flux density of the magnetic gap is The disadvantages are that the magnetic flux density is reduced and the distribution of magnetic flux density is non-uniform.

Therefore, the present invention covers the movable parts with a cover (1o) to protect the movable parts from external shocks as shown in FIG. The leaking part of the circuit is the magnet (6a
), the top of the yoke (5c), and the magnet (6b)
An iron piece (11) with good magnetic conductivity is pasted so as to touch and straddle the upper part of the yoke (5c), and the above cover (5c) is attached.
10) is constructed such that when the objective lens driving device is coated, the leakage magnetic flux (β) of the magnetic gap passes through the inside of the iron piece (II).6 The present invention has the above structure, so that the objective lens By covering the drive device with the cover (10), the magnetic circuit is closed, and leakage magnetic flux (β) from the magnetic gap can be reduced.

Therefore, the magnetic flux density of the magnetic gap becomes high, making it possible to increase the driving sensitivity, and also making it possible to uniformly distribute the magnetic flux density, thereby making it possible to reduce the tilt vibration of the objective lens.

〔Effect of the invention〕

As explained above, according to the present invention, the magnetic flux density of the magnetic gap in the magnetic circuit is increased and a uniform magnetic flux distribution is obtained, so it is possible to increase the drive sensitivity and reduce the tilt vibration of the objective lens. This has the effect of being able to

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an objective lens drive device showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the force generated when current flows through the focus direction drive coil and the force generated in the wire, Fig. 3 is an explanatory diagram showing the force generated when a current flows through the track direction drive coil and the force generated in the wire, Fig. 4 is a perspective view for explaining the present invention in detail, and Fig. 5 is a conventional FIG. 2 is a perspective view for explaining leakage magnetic flux of a magnetic gap in the objective lens driving device. 1... Objective lens 3... Focus coil (focus direction drive coil) 4... Track coil (track direction drive coil)
6a, 6b...Magnet 10...Cover 11
... Iron piece (preventive means) Agent Patent attorney Inoue - Rikitsutsu 1 Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) An objective lens that focuses light onto an information recording medium having a recording track, a focus direction drive coil that drives the objective lens in the focus direction, and a track direction that drives the objective lens in a direction substantially perpendicular to the recording track direction. An objective lens comprising: a drive coil; a magnet disposed opposite each of the drive coils to form a magnetic circuit; and a prevention means for preventing leakage of magnetic flux from an open portion of the magnetic circuit. Drive device. (2) The objective lens driving device according to claim 1, wherein the prevention means includes a magnetically permeable material adhered to the leakage portion of the upper part of the magnet. (3) The objective lens drive device according to claim 1, wherein the prevention means includes a magnetic conductive material affixed to the upper inner surface of the cover, facing the magnet leakage portion.